Publications

<span>The challenges of restoration in dryland ecosystems are growing due to a rise in anthropogenic disturbance and increasing aridity. Plant functional traits are often used to predict plant performance and can offer a window into potential outcomes of restoration efforts across environmental gradients. We analyzed a database including 15 yr of seeding outcomes across 150 sites on the Colorado Plateau, a cold desert ecoregion in the western United States, and analyzed the independent and interactive effects of functional traits (seed mass, height, and specific leaf area) and local biologically relevant climate variables on seeding success. We predicted that the best models would include an interaction between plant traits and climate, indicating a need to match the right trait value to the right climate conditions to maximize seeding success. Indeed, we found that both plant height and seed size significantly interacted with temperature seasonality, with larger seeds and taller plants performing better in more seasonal environments. We also determined that these trait?environment patterns are not influenced by whether a species is native or nonnative. Our results inform the selection of seed mixes for restoring areas with specific climatic conditions, while also demonstrating the strong influence of temperature seasonality on seeding success in the Colorado Plateau region.</span>

<span>Microbial activity increases after rewetting dry soil, resulting in a pulse of carbon mineralization and nutrient availability. The biogeochemical responses to wet-up are reasonably well understood and known to be microbially mediated. Yet, the population level dynamics, and the resulting changes in microbial community patterns, are not well understood as ecological phenomena. Here, we used sequencing of 16S rRNA genes coupled with heavy water (H218O) DNA quantitative stable isotope probing to estimate population-specific rates of growth and mortality in response to a simulated wet-up event in a California annual grassland soil. Bacterial growth and mortality responded rapidly to wet-up, within 3 h, and continued throughout the 168 h incubation, with patterns of sequential growth observed at the phylum level. Of the 37 phyla detected in the prewet community, growth was found in 18 phyla while mortality was measured in 26 phyla. Rapid growth and mortality rates were measurable within 3 h of wet-up but had contrasting characteristics; growth at 3 h was dominated by select taxa within the Proteobacteria and Firmicutes, whereas mortality was taxonomically widespread. Furthermore, across the community, mortality exhibited density-independence, consistent with the indiscriminate shock resulting from dry-down and wet-up, whereas growth was density-dependent, consistent with control by competition or predation. Total aggregated growth across the community was highly correlated with total soil CO2 production. Together, these results illustrate how previously “invisible” population responses can translate quantitatively to emergent observations of ecosystem-scale biogeochemistry.</span>

<span>Forests absorb a large fraction of anthropogenic CO2 emission, but their ability to continue to act as a sink under climate change depends in part on plant species undergoing rapid adaptation. Yet models of forest response to climate change currently ignore local adaptation as a response mechanism. Thus, considering the evolution of intraspecific trait variation is necessary for reliable, long-term species and climate projections. Here, we combine ecophysiology and predictive climate modeling with analyses of genomic variation to determine whether sugar and starch storage, energy reserves for trees under extreme conditions, have the heritable variation and genetic diversity necessary to evolve in response to climate change within populations of black cottonwood (Populus trichocarpa). Despite current patterns of local adaptation and extensive range-wide heritable variation in storage, we demonstrate that adaptive evolution in response to climate change will be limited by a lack of heritable variation within northern populations and by a need for extreme genetic changes in southern populations. Our method can help design more targeted species management interventions and highlights the power of using genomic tools in ecological prediction to scale from molecular to regional processes to determine the ability of a species to respond to future climates.</span>

<span>Globally, soils store two to three times as much carbon as currently resides in the atmosphere, and it is critical to understand how soil greenhouse gas (GHG) emissions and uptake will respond to ongoing climate change. In particular, the soil-to-atmosphere CO2 flux, commonly though imprecisely termed soil respiration (RS), is one of the largest carbon fluxes in the Earth system. An increasing number of high-frequency RS measurements (typically, from an automated system with hourly sampling) have been made over the last two decades; an increasing number of methane measurements are being made with such systems as well. Such high frequency data are an invaluable resource for understanding GHG fluxes, but lack a central database or repository. Here we describe the lightweight, open-source COSORE (COntinuous SOil REspiration) database and software, that focuses on automated, continuous and long-term GHG flux datasets, and is intended to serve as a community resource for earth sciences, climate change syntheses and model evaluation. Contributed datasets are mapped to a single, consistent standard, with metadata on contributors, geographic location, measurement conditions and ancillary data. The design emphasizes the importance of reproducibility, scientific transparency and open access to data. While being oriented towards continuously measured RS, the database design accommodates other soil-atmosphere measurements (e.g. ecosystem respiration, chamber-measured net ecosystem exchange, methane fluxes) as well as experimental treatments (heterotrophic only, etc.). We give brief examples of the types of analyses possible using this new community resource and describe its accompanying R software package.</span>

<span>Effects of riparian vegetation on fluvial sediment dynamics depend on morphological traits of the constituent species. Determining the effects of different morphological guilds on sedimentation rates, as influenced by multiple aspects of dam operations, can help identify viable strategies for streamflow and vegetation management to achieve riparian resource goals. Plants of increasing size and branching density or complexity have been found to have greater effects on sedimentation in free-flowing systems; however, this relationship could differ in regulated rivers. We tested the hypothesis that plant guilds of increasing height and branching complexity would be positively associated with sedimentation rates on 23 sandbars deposited in zones of recirculating flow (eddies) along the Colorado River in Grand Canyon. We used an image-based vegetation classification and digital elevation models from annual topographic surveys to track associations between six plant morphological guilds and topographic change over 5?years. Vegetation had significant associations with deposition after accounting for geomorphic setting, but the ordinal guild scale was not positively correlated with deposition magnitude. Instead, low-statured rhizomatous and herbaceous guilds were particularly effective at capturing sediment in the separation zone of sandbars, whereas tall herbs and large shrubs were most effective at capturing sediment in reattachment zones. These nuanced interactions between geomorphic position and morphological guild may be a direct consequence of flow regulation through modifications to physical deposition and erosion processes. Flow regulation may also select for a narrow subset of morphological guilds, reducing the diversity of vegetation feedbacks on sedimentation and emphasizing geomorphic drivers.</span>

<span>Climate warming is widely expected to affect rice yields, but results are equivocal and variation in rice cropping systems and climatic conditions complicates country-scale yield assessments. Here we show, through meta–analysis of field warming experiments, that yield responses to warming differ strongly between China's rice cropping systems. Whereas warming increases yields in “single rice” systems, it decreases yields in “middle rice” systems and has contrasting effects for early and late rice in “double rice” systems. We further show that the contribution of these cropping systems to China's total rice production has shifted dramatically over recent decades. We estimate that if the present structure of rice cropping systems persists, warming will reduce China's total rice production by 5.0% in 2060. However, if the recent decline in the area of double rice systems continues, China's rice production may decrease by 13.5%. Our results underline the need for maintaining the current area of China's “double rice” cropping system and for technological innovations in multiple rice cropping systems to ensure food security in a warming climate.</span>

<span>Climate warming affects soil carbon (C) dynamics, with possible serious consequences for soil C stocks and atmospheric CO2 concentrations. However, the mechanisms underlying changes in soil C storage are not well understood, hampering long-term predictions of climate C-feedbacks. The activity of the extracellular enzymes ligninase and cellulase can be used to track changes in the predominant C sources of soil microbes and can thus provide mechanistic insights into soil C loss pathways. Here we show, using meta-analysis, that reductions in soil C stocks with warming are associated with increased ratios of ligninase to cellulase activity. Furthermore, whereas long-term (≥5 years) warming reduced the soil recalcitrant C pool by 14%, short-term warming had no significant effect. Together, these results suggest that warming stimulates microbial utilization of recalcitrant C pools, possibly exacerbating long-term climate-C feedbacks.</span>

<span>Increased human-derived nitrogen (N) deposition to terrestrial ecosystems has resulted in widespread phosphorus (P) limitation of net primary productivity. However, it remains unclear if and how N-induced P limitation varies over time. Soil extracellular phosphatases catalyze the hydrolysis of P from soil organic matter, an important adaptive mechanism for ecosystems to cope with N-induced P limitation. Here we show, using a meta-analysis of 140 studies and 668 observations worldwide, that N stimulation of soil phosphatase activity diminishes over time. Whereas short-term N loading (≤5 years) significantly increased soil phosphatase activity by 28%, long-term N loading had no significant effect. Nitrogen loading did not affect soil available P and total P content in either short- or long-term studies. Together, these results suggest that N-induced P limitation in ecosystems is alleviated in the long-term through the initial stimulation of soil phosphatase activity, thereby securing P supply to support plant growth. Our results suggest that increases in terrestrial carbon uptake due to ongoing anthropogenic N loading may be greater than previously thought.</span>

<span>The addition of glucose to soil has long been used to study the metabolic activity of microbes in soil; however, the response of the microbial ecophysiology remains poorly characterized. To address this, we sequenced the metagenomes and metatranscriptomes of glucose-amended soil microbial communities in a laboratory incubation.</span>

<span>Multiple lines of evidence have demonstrated the persistence of global land carbon (C) sink during the past several decades. However, both annual net ecosystem productivity (NEP) and its inter-annual variation (IAV</span><span class="inline-formula">_NEP</span><span>) keep varying over space. Thus, identifying local indicators for the spatially varying NEP and IAV</span><span class="inline-formula">_NEP</span><span> is critical for locating the major and sustainable C sinks on land. Here, based on daily NEP observations from FLUXNET sites and large-scale estimates from an atmospheric-inversion product, we found a robust logarithmic correlation between annual NEP and seasonal carbon uptake–release ratio (i.e. </span><span class="inline-formula"><i>U</i> ∕ <i>R</i></span><span>). The cross-site variation in mean annual NEP could be logarithmically indicated by </span><span class="inline-formula"><i>U</i> ∕ <i>R</i></span><span>, while the spatial distribution of IAV</span><span class="inline-formula">_NEP</span><span> was associated with the slope (i.e. </span><span class="inline-formula"><i>β</i></span><span>) of the logarithmic correlation between annual NEP and </span><span class="inline-formula"><i>U</i> ∕ <i>R</i></span><span>. Among biomes, for example, forests and croplands had the largest </span><span class="inline-formula"><i>U</i> ∕ <i>R</i></span><span> ratio (1.06 </span><span class="inline-formula">±</span><span> 0.83) and </span><span class="inline-formula"><i>β</i></span><span> (473 </span><span class="inline-formula">±</span><span> 112 g C m</span><span class="inline-formula">⁻²</span><span> yr</span><span class="inline-formula">⁻¹</span><span>), indicating the highest NEP and IAV</span><span class="inline-formula">_NEP</span><span> in forests and croplands, respectively. We further showed that these two simple indicators could directly infer the spatial variations in NEP and IAV</span><span class="inline-formula">_NEP</span><span> in global gridded NEP products. Overall, this study provides two simple local indicators for the intricate spatial variations in the strength and stability of land C sinks. These indicators could be helpful for locating the persistent terrestrial C sinks and provide valuable constraints for improving the simulation of land–atmospheric C exchanges.</span>

<span>Climate change is altering disturbance regimes outside historical norms, which can impact biodiversity by selecting for plants with particular traits. The relative impact of disturbance characteristics on plant traits and community structure may be mediated by environmental gradients. We aimed to understand how wildfire impacted understory plant communities and plant regeneration strategies along gradients of environmental conditions and wildfire characteristics in boreal forests. We established 207 plots (60?m2) in recently burned stands and 133 plots in mature stands with no recent fire history in comparable gradients of stand type, site moisture (drainage) and soil organic layer (SOL) depth in two ecozones in Canada's Northwest Territories. At each plot, we recorded all vascular plant taxa in the understory and measured the regeneration strategy (seeder, resprouter, survivor) in burned plots, along with seedbed conditions (mineral soil and bryophyte cover). Dispersal, longevity and growth form traits were determined for each taxon. Fire characteristics measured included proportion of pre-fire SOL combusted (fire severity), date of burn (fire seasonality) and pre-fire stand age (time following fire). Results showed understory community composition was altered by fire. However, burned and mature stands had similar plant communities in wet sites with deep SOL. In the burned plots, regeneration strategies were determined by fire severity, drainage and pre- and post-fire SOL depth. Resprouters were more common in wet sites with deeper SOL and lower fire severity, while seeders were associated with drier sites with thinner SOL and greater fire severity. This led to drier burned stands being compositionally different from their mature counterparts and seedbed conditions were important. Our study highlights the importance of environment?wildfire interactions in shaping plant regeneration strategies and patterns of understory plant community structure across landscapes, and the overriding importance of SOL depth and site drainage in mediating fire severity, plant regeneration and community structure.</span>

<span>Boreal wildfires are increasing in intensity, extent, and frequency, potentially intensifying carbon emissions and transitioning the region from a globally significant carbon sink to a source. The productive southern boreal forests of central Canada already experience relatively high frequencies of fire, and as such may serve as an analog of future carbon dynamics for more northern forests. Fire?carbon dynamics in southern boreal systems are relatively understudied, with limited investigation into the drivers of pre-fire carbon stocks or subsequent combustion. As part of NASA's Arctic-Boreal Vulnerability Experiment, we sampled 79 stands (47 burned, 32 unburned) throughout central Saskatchewan to characterize above- and belowground carbon stocks and combustion rates in relation to historical land use, vegetation characteristics, and geophysical attributes. We found southern boreal forests emitted an average of 3.3 ± 1.1 kg C/m2 from field sites. The emissions from southern boreal stands varied as a function of stand age, fire weather conditions, ecozone, and soil moisture class. Sites affected by historical timber harvesting had greater combustion rates due to faster carbon stock recovery rates than sites recovering from wildfire events, indicating that different boreal forest land use practices can generate divergent carbon legacy effects. We estimate the 2015 fire season in Saskatchewan emitted a total of 36.3 ± 15.0 Tg C, emphasizing the importance of southern boreal fires for regional carbon budgets. Using the southern boreal as an analog, the northern boreal may undergo fundamental shifts in forest structure and carbon dynamics, becoming dominated by stands &lt;70 years old that hold 2?7 kg C/m2 less than current mature northern boreal stands. Our latitudinal approach reinforces previous studies showing that northern boreal stands are at a high risk of holding less carbon under changing disturbance conditions.</span>

<span>It is well-known that global warming has effects on high-latitude tundra underlain with permafrost. This leads to a severe concern that decomposition of soil organic carbon (SOC) previously stored in this region, which accounts for about 50% of the world’s SOC storage, will cause positive feedback that accelerates climate warming. We have previously shown that short-term warming (1.5 years) stimulates rapid, microbe-mediated decomposition of tundra soil carbon without affecting the composition of the soil microbial community (based on the depth of 42684 sequence reads of 16S rRNA gene amplicons per 3 g of soil sample).</span>

<span>One major source of uncertainties in the estimation of soil organic carbon (SOC) dynamics is carbon (C) residence time, an important parameter in terrestrial ecosystem C cycling models. To better predict terrestrial dynamics, C residence time and its controlling factors need to be well quantified and investigated. In this study, we applied a data assimilation approach to quantify the residence times of different soil C pools on the Tibetan Plateau, based on incubated soil carbon dioxide (CO2) efflux data. We also assessed the effects of soil properties on C residence times. Our results showed that the residence times of active (RTA) and slow (RTS) C pools were well estimated through data assimilation. Soil physical, chemical, and microbial properties significantly regulated RTA and RTS. The RTA was higher in soils with high clay contents (R2 = 0.52, p &lt; 0.01) and low microbial quotients (qMB) (R2 = 0.55, p &lt; 0.01), whereas, the RTS was higher in soils with high clay contents (R2 = 0.76, p &lt; 0.01), high C:N ratios (R2 = 0.44, p &lt; 0.05), low qMBvalues (R2 = 0.50, p &lt; 0.05), and low soil pH values (R2 = 0.80, p &lt; 0.01). Structural equation modeling (SEM) analyses indicated that the model could explain 55% and 91% of the variations in the RTA and RTS, respectively. The qMB was the key factor in regulating the RTA, while soil pH was the crucial variable in controlling the RTS. These results demonstrated that the major controlling factors on the RTA and RTS were different. Considering these variables and their different controls on residence times of different soil C pools could provide more accurate estimation of terrestrial C cycles, and prediction of future C-climate feedbacks.</span>

<span>Non-structural carbohydrates (NSCs) are necessary for plant growth and affected by plant water status, but the temporal dynamics of water stress impacts on NSC are not well understood. We evaluated how seasonal NSC concentrations varied with plant water status (predawn xylem water potential, ) and air temperature (T) in the evergreen desert shrub Larrea tridentata. Aboveground sugar and starch concentrations were measured weekly or monthly for ~1.5 years on 6 -12 shrubs simultaneously instrumented with automated stem psychrometers; leaf photosynthesis (Anet) was measured monthly for 1 year. Leaf sugar increased during the dry, premonsoon period, associated with lower  (greater water stress) and high T. Leaf sugar accumulation coincided with declines in leaf starch and stem sugar, suggesting the prioritization of leaf sugar during low photosynthetic uptake. Leaf starch was strongly correlated with Anet and peaked during the spring and monsoon seasons, while stem starch remained relatively constant except for depletion during the monsoon. Recent photosynthate appeared sufficient to support spring growth, while monsoon growth required the remobilization of stem starch reserves. The coordinated responses of different NSC fractions to water status, photosynthesis, and growth demands suggest that NSCs serve multiple functions under extreme environmental conditions, including severe drought.</span>

Plant species are characterized along a spectrum of isohydry to anisohydry depending on their regulation of water potential (?), but the plasticity of hydraulic strategies is largely unknown. The role of environmental drivers was evaluated in the hydraulic behavior of Larrea tridentata, a drought-tolerant desert shrub that withstands a wide range of environmental conditions. With a 1.5 yr time-series of 2324 in situ measurements of daily predawn and midday ?, the temporal variability of hydraulic behavior was explored in relation to soil water supply, atmospheric demand and temperature. Hydraulic behavior in Larrea was highly dynamic, ranging from partial isohydry to extreme anisohydry. Larrea exhibited extreme anisohydry under wet soil conditions corresponding to periods of high productivity, whereas partial isohydry was exhibited after prolonged dry or cold conditions, when productivity was low. Environmental conditions can strongly influence plant hydraulic behavior at relatively fast timescales, which enhances our understanding of plant drought responses. Although species may exhibit a dominant hydraulic behavior, variable environmental conditions can prompt plasticity in ? regulation, particularly for species in seasonally dry climates.

Pinyon-juniper (PJ) plant communities cover a large area across North America and provide critical habitat for wildlife, biodiversity and ecosystem functions, and rich cultural resources. These communities occur across a variety of environmental gradients, disturbance regimes, structural conditions and species compositions, including three species of juniper and two species of pinyon. PJ communities have experienced substantial changes in recent decades and identifying appropriate management strategies for these diverse communities is a growing challenge. Here, we surveyed the literature and compiled 441 studies to characterize patterns in research on PJ communities through time, across geographic space and climatic conditions, and among focal species. We evaluate the state of knowledge for three focal topics: 1) historical stand dynamics and responses to disturbance, 2) land management actions and their effects, and 3) potential future responses to changing climate. We identified large and potentially important gaps in our understanding of pinyon-juniper communities both geographically and topically. The effect of drought on Pinus edulis, the pinyon pine species in eastern PJ communities was frequently addressed, while few studies focused on drought effects on Pinus monophylla, which occurs in western PJ communities. The largest proportion of studies that examined land management actions only measured their effects for one year. Grazing was a common land-use across the geographic range of PJ communities yet was rarely studied. We found only 39 studies that had information on the impacts of anthropogenic climate change and most were concentrated on Pinus edulis. These results provide a synthetic perspective on PJ communities that can help natural resource managers identify relevant knowledge needed for decision-making and researchers design new studies to fill important knowledge gaps.

<span>We conducted a large-scale, multiple-year study in harvested areas of Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) forests in western Washington, examining the effectiveness of control methods on the widespread invasive shrub Scotch broom [Cytisus scoparius (L.) Link]. We tested both chemical and physical control methods, using three different approaches that are management relevant: (1) triclopyr, a POST herbicide, at different times of year and on different-sized plants; (2) cutting (or brushcutting) of mature individuals; and (3) scarification of soil surface to remove seedlings once versus multiple times. We measured initial mortality, seed germination, and percent cover of C. scoparius in plots for 3 yr following treatments. Triclopyr treatment resulted in greater mortality and reduced percent cover compared with all other treatments with the effect persisting for 2 yr after spraying. Further, triclopyr had the same effect on C. scoparius cover and mortality irrespective of time of year applied. Similar to soil scarification, triclopyr treatments resulted in a flush of seedlings, suggesting that removal of conspecific competitors and not soil disturbance per se promotes seed germination. Brushcutting was generally effective in reducing C. scoparius cover in the short term, but effects did not persist as long as triclopyr treatments, in part due to large differences in stump resprouting rates across sites. Soil scarification to remove seedlings, even over multiple years, did not result in reduced C. scoparius cover. Triclopyr is an effective approach for controlling both emerging and established stands of C. scoparius.</span>

<span>Our aim is to use elevational gradients to quantify the relationship between temperature and ecosystem functioning. Ecosystem functions such as decomposition, nutrient cycling and carbon storage are linked with the amount of microbial biomass in the soil. Previous studies have shown variable relationships between elevation and soil microbial biomass (SMB). Understanding the biological mechanisms linking SMB with elevational gradients will shed light on the environmental impacts of global warming. Location Global. Time period 2002?2018. Major taxa studied Soil microbes. Method We performed a global meta-analysis of the relationships between SMB and elevation. Data were collected from 59 studies of 73 elevational transects from around the world. Results We found no consistent global relationship between SMB and elevation. SMB increased significantly with elevation in the tropics and subtropics, but not in other climate zones. However, we found consistent positive relationships between SMB, soil organic carbon and total nitrogen concentrations. Main conclusions Our results suggest that global warming will impact tropical and subtropical ecosystems more severely than colder regions. Tropical ecosystems, already at risk from species extinctions, will likely experience declines in SMB as the climate warms, resulting in losses of fundamental ecosystem functions such as nutrient cycling and carbon storage.</span>

<span>As Arctic soils warm, thawed permafrost releases nitrogen (N) that could stimulate plant productivity and thus offset soil carbon losses from tundra ecosystems. Although mycorrhizal fungi could facilitate plant access to permafrost-derived N, their exploration capacity beyond host plant root systems into deep, cold active layer soils adjacent to the permafrost table is unknown. We characterized root-associated fungi (RAF) that colonized ericoid (ERM) and ectomycorrhizal (ECM) shrub roots and occurred below the maximum rooting depth in permafrost thaw-front soil in tussock and shrub tundra communities. We explored the relationships between root and thaw front fungal composition and plant uptake of a 15N tracer applied at the permafrost boundary. We show that ERM and ECM shrubs associate with RAF at the thaw front providing evidence for potential mycelial connectivity between roots and the permafrost boundary. Among shrubs and tundra communities, RAF connectivity to the thaw boundary was ubiquitous. The occurrence of particular RAF in both roots and thaw front soil was positively correlated with 15N recovered in shrub biomass Taxon-specific RAF associations could be a mechanism for the vertical redistribution of deep, permafrost-derived nutrients, which may alleviate N limitation and stimulate productivity in warming tundra.</span>

<span>Phosphorus (P) limitation of aboveground plant production is usually assumed to occur in tropical regions but rarely elsewhere. Here we report that such P limitation is more widespread and much stronger than previously estimated. In our global meta-analysis, almost half (46.2%) of 652 P-addition field experiments reveal a significant P limitation on aboveground plant production. Globally, P additions increase aboveground plant production by 34.9% in natural terrestrial ecosystems, which is 7.0–15.9% higher than previously suggested. In croplands, by contrast, P additions increase aboveground plant production by only 13.9%, probably because of historical fertilizations. The magnitude of P limitation also differs among climate zones and regions, and is driven by climate, ecosystem properties, and fertilization regimes. In addition to confirming that P limitation is widespread in tropical regions, our study demonstrates that P limitation often occurs in other regions. This suggests that previous studies have underestimated the importance of altered P supply on aboveground plant production in natural terrestrial ecosystems.</span>

Plants are thought to be limited by phosphorus (P) especially in tropical regions. Here, Hou et al. report a meta-analysis of P fertilization experiments to show widespread P limitation on plant growth across terrestrial ecosystems modulated by climate, ecosystem properties, and fertilization regimes

<span>Through agriculture and industry, humans are increasing the deposition and availability of nitrogen (N) in ecosystems worldwide. Carbon (C) isotope tracers provide useful insights into soil C dynamics, as they allow to study soil C pools of different ages. We evaluated to what extent N enrichment affects soil C dynamics in experiments that applied C isotope tracers.</span>

<span>Nitrogen (N2)-fixing moss microbial communities play key roles in nitrogen cycling of boreal forests. Forest type and leaf litter inputs regulate moss abundance, but how they control moss microbiomes and N2-fixation remains understudied. We examined the impacts of forest type and broadleaf litter on microbial community composition and N2-fixation rates of Hylocomium splendens and Pleurozium schreberi. We conducted a moss transplant and leaf litter manipulation experiment at three sites with paired paper birch (Betula neoalaskana) and black spruce (Picea mariana) stands in Alaska. We characterized bacterial communities using marker gene sequencing, determined N2-fixation rates using stable isotopes (15N2) and measured environmental covariates. Mosses native to and transplanted into spruce stands supported generally higher N2-fixation and distinct microbial communities compared to similar treatments in birch stands. High leaf litter inputs shifted microbial community composition for both moss species and reduced N2-fixation rates for H. splendens, which had the highest rates. N2-fixation was positively associated with several bacterial taxa, including cyanobacteria. The moss microbiome and environmental conditions controlled N2-fixation at the stand and transplant scales. Predicted shifts from spruce- to deciduous-dominated stands will interact with the relative abundances of mosses supporting different microbiomes and N2-fixation rates, which could affect stand-level N inputs.</span>

<span>Organic matter input to soils can accelerate the decomposition of native soil carbon (C), a process called the priming effect. Priming is ubiquitous and exhibits some consistent patterns, but a general explanation remains elusive, in part because of variation in the response across different ecosystems, and because of a diversity of proposed mechanisms, including microbial activation, stoichiometry, and community shifts. Here, we conducted five-week incubations of four soils (grassland, piñon-juniper, ponderosa pine, mixed conifer), varying the amount of substrate added (as 13C-glucose, either 350 or 1000 μg C g−1 week−1) and either with no added nitrogen (N), or with sufficient N (as NH4NO3) to bring the C-to-N ratio of the added substrate to 10. Using four different ecosystems enabled testing the generality of mechanisms underlying the priming effect. The responses of priming to the amount and C-to-N ratio of the added substrate were consistent across ecosystems: priming increased with the rate of substrate addition and declined when the C-to-N ratio of the substrate was reduced. However, structural equation models failed to confirm intermediate responses postulated to mediate the priming effect, including responses postulated to be mediated by stoichiometry and microbial activation. Specifically, priming was not clearly associated with changes in microbial biomass or turnover, nor with extracellular enzyme activities or the microbial C-to-N ratio. The strongest explanatory pathways in the structural equation models were the substrate, soil, and C-to-N ratio treatments themselves, with no intermediates, suggesting that either these measurements lacked sufficient sensitivity to reveal causal relationships, or the actual drivers for priming were not included in the ancillary measurements. While we observed consistent changes in priming caused by the amount and C-to-N ratio of the added substrate across a wide array of soils, our findings did not clearly conform to common models offered for the priming effect. Because priming is a residual flux involving diverse substrates of varying chemical composition, a simple and generalizable explanation of the phenomenon may be elusive.</span>

<span>Large-scale primary native broadleaf forests (BF) have been converted to secondary forests (SF) and plantation forests (PF) in subtropical China over the past decades. However, how and what magnitude of plant and soil carbon (C), nitrogen (N), and phosphorus (P) stocks and stoichiometry are affected by forest conversion is still vague. Here, we addressed this issue by systematically measuring tree biomass and the C, N, and P concentrations in tree organs and soils (0–100 cm) collected from 300 plots in Fujian province. With forest conversion of BF to PF, the tree C, N, and P stocks declined by 43.8, 47.9, and 63.1%, respectively, and the soil C and N stocks across whole soil depth decreased by 19.1% and 13.0%, respectively, and these decreases were more evident after conversion of BF to PF than SF. However, soil P stock showed a tendency of decreasing at 0–20 cm soil depth but increasing at 20–100 cm soil depth following conversion of BF to SF and PF. This unconformity of the vertical pattern of P stock in contrast to C and N stocks, was perhaps due to higher C and N inputs and greater P uptake from the subsoil and its redistribution to the topsoil in BF than in SF and PF. The tree and soil C, N, and P stoichiometry was strongly related to tree biomass, indicating that tree biomass was a vital factor driving soil inputs and retention of nutrients, and thus affecting their stoichiometry. The leaf N:P ratios ranging from 16.7 to 17.2 at our study sites suggested that co-limitations of N and P for forest growth could occur in the studied region. Our results provided insights into the C, N, and P linkages between soils and trees as affected by forest conversion, and advised that predicting these linkages could be an effective approach to identify the impacts of forest conversion, thereby implementing targeted conservation and rehabilitation actions.</span>

<span>The dynamic equilibrium of mass and energy movement in ecosystems is an important basis for the Earth system to nurture and maintain biodiversity. Since the Industrial Revolution, human activities have caused the carbon exchange between terrestrial ecosystems and the atmosphere to be at dynamic disequilibrium. This paper examines a dynamic disequilibrium hypothesis for the carbon cycle of terrestrial ecosystems. The hypothesis suggests that the dynamic disequilibrium is caused by interactions of four basic properties of internal processes of the terrestrial carbon cycle with five types of external drivers. Based on these internal properties and external drivers, this paper summarizes the expression phenomena of the dynamic disequilibrium of terrestrial carbon cycle at different time and space scales, and discusses its detection methods from the perspective of observations, experiments and models. The dynamic disequilibrium hypothesis for terrestrial carbon cycle not only helps us understand the complex terrestrial carbon-cycle phenomenon, but also provides a new theoretical framework for predicting the future terrestrial carbon sink dynamics.</span>

<span>Will mature forests absorb enough carbon from the atmosphere to mitigate climate change as levels of carbon dioxide increase? An experiment in a eucalyptus forest provides fresh evidence.</span>

<span>Cities and their associated urban heat islands are ideal natural laboratories for evaluating the response of plant phenology to warming conditions. In this study, we demonstrate that the satellite-derived start of season for plants occurred earlier but showed less covariation with temperature in most of the large 85 cities across the conterminous United States for the period 2001–2014. The results show a reduction in the response of urban phenology to temperature and imply that, in nonurban environments, the onset of spring phenology will likely advance but will slow down as the general trend toward warming continues.Urbanization has caused environmental changes, such as urban heat islands (UHIs), that affect terrestrial ecosystems. However, how and to what extent urbanization affects plant phenology remains relatively unexplored. Here, we investigated the changes in the satellite-derived start of season (SOS) and the covariation between SOS and temperature (RT) in 85 large cities across the conterminous United States for the period 2001–2014. We found that 1) the SOS came significantly earlier (6.1 ± 6.3 d) in 74 cities and RT was significantly weaker (0.03 ± 0.07) in 43 cities when compared with their surrounding rural areas (P &amp;amp;lt; 0.05); 2) the decreased magnitude in RT mainly occurred in cities in relatively cold regions with an annual mean temperature &amp;amp;lt;17.3 °C (e.g., Minnesota, Michigan, and Pennsylvania); and 3) the magnitude of urban−rural difference in both SOS and RT was primarily correlated with the intensity of UHI. Simulations of two phenology models further suggested that more and faster heat accumulation contributed to the earlier SOS, while a decrease in required chilling led to a decline in RT magnitude in urban areas. These findings provide observational evidence of a reduced covariation between temperature and SOS in major US cities, implying the response of spring phenology to warming conditions in nonurban environments may decline in the warming future.</span>

<span>Growth of soil microorganisms is often described as carbon limited, and adding labile carbon to soil often results in a transient and large increase in respiration. In contrast, soil microbial biomass changes little, suggesting that growth and respiration are decoupled in response to a carbon pulse. Alternatively, measuring bulk responses of the entire community (total respiration and biomass) could mask ecologically important variation among taxa in response to the added carbon. Here, we assessed taxon-specific variation in cellular growth (measured as DNA synthesis) and metabolic activity (measured as rRNA synthesis) following glucose addition to soil using quantitative stable isotope probing with H218O. We found that glucose addition altered rates of DNA and rRNA synthesis, but the effects were strongly taxon specific: glucose stimulated growth and rRNA transcription for some taxa, and suppressed these for others. These contrasting taxon-specific responses could explain the small and transient changes in total soil microbial biomass. Responses to glucose were not well predicted by a priori assignments of taxa into copiotrophic or oligotrophic categories. Across all taxa, rates of DNA and rRNA synthesis changed in parallel, indicating that growth and activity were coupled, and the degree of coupling was unaffected by glucose addition. This pattern argues against the idea that labile carbon addition causes a large reduction in metabolic growth efficiency; rather, the large pulse of respiration observed with labile substrate addition is more likely to be the result of rapid turnover of microbial biomass, possibly due to trophic interactions. Our results support a strong connection between rRNA synthesis and bacterial growth, and indicate that taxon-specific responses among soil bacteria can buffer responses at the scale of the whole community.</span>

<span>Despite the wide application of meta-analysis in ecology, some of the traditional methods used for meta-analysis may not perform well given the type of data characteristic of ecological meta-analyses. We reviewed published meta-analyses on the ecological impacts of global climate change, evaluating the number of replicates used in the primary studies (ni) and the number of studies or records (k) that were aggregated to calculate a mean effect size. We used the results of the review in a simulation experiment to assess the performance of conventional frequentist and Bayesian meta-analysis methods for estimating a mean effect size and its uncertainty interval. Our literature review showed that ni and k were highly variable, distributions were right-skewed and were generally small (median ni = 5, median k = 44). Our simulations show that the choice of method for calculating uncertainty intervals was critical for obtaining appropriate coverage (close to the nominal value of 0.95). When k was low (&lt;40), 95% coverage was achieved by a confidence interval (CI) based on the t distribution that uses an adjusted standard error (the Hartung?Knapp?Sidik?Jonkman, HKSJ), or by a Bayesian credible interval, whereas bootstrap or z distribution CIs had lower coverage. Despite the importance of the method to calculate the uncertainty interval, 39% of the meta-analyses reviewed did not report the method used, and of the 61% that did, 94% used a potentially problematic method, which may be a consequence of software defaults. In general, for a simple random-effects meta-analysis, the performance of the best frequentist and Bayesian methods was similar for the same combinations of factors (k and mean replication), though the Bayesian approach had higher than nominal (&gt;95%) coverage for the mean effect when k was very low (k &lt; 15). Our literature review suggests that many meta-analyses that used z distribution or bootstrapping CIs may have overestimated the statistical significance of their results when the number of studies was low; more appropriate methods need to be adopted in ecological meta-analyses.</span>

<span>Fire activity is changing dramatically across the globe, with uncertain effects on ecosystem processes, especially below-ground. Fire-driven losses of soil carbon (C) are often assumed to occur primarily in the upper soil layers because the repeated combustion of above-ground biomass limits organic matter inputs into surface soil. However, C losses from deeper soil may occur if frequent burning reduces root biomass inputs of C into deep soil layers or stimulates losses of C via leaching and priming. To assess the effects of fire on soil C, we sampled 12 plots in a 51-year-long fire frequency manipulation experiment in a temperate oak savanna, where variation in prescribed burning frequency has created a gradient in vegetation structure from closed-canopy forest in unburned plots to open-canopy savanna in frequently burned plots. Soil C stocks were nonlinearly related to fire frequency, with soil C peaking in savanna plots burned at an intermediate fire frequency and declining in the most frequently burned plots. Losses from deep soil pools were significant, with the absolute difference between intermediately burned plots versus most frequently burned plots more than doubling when the full 1 m sample was considered rather than the top 0?20 cm alone (losses of 98.5 Mg C/ha [?76%] and 42.3 Mg C/ha [?68%] in the full 1 m and 0?20 cm layers respectively). Compared to unburned forested plots, the most frequently burned plots had 65.8 Mg C/ha (?58%) less C in the full 1 m sample. Root biomass below the top 20 cm also declined by 39% with more frequent burning. Concurrent fire-driven losses of nitrogen and gains in calcium and phosphorus suggest that burning may increase nitrogen limitation and play a key role in the calcium and phosphorus cycles in temperate savannas. Synthesis. Our results illustrate that fire-driven losses in soil C and root biomass in deep soil layers may be critical factors regulating the net effect of shifting fire regimes on ecosystem C in forest-savanna transitions. Projected changes in soil C with shifting fire frequencies in savannas may be 50% too low if they only consider changes in the topsoil.</span>

<span>In trees, large uncertainties remain in how nonstructural carbohydrates (NSCs) respond to variation in water availability in natural, intact ecosystems. Variation in NSC pools reflects temporal fluctuations in supply and demand, as well as physiological coordination across tree organs in ways that differ across species and NSC fractions (e.g., soluble sugars vs starch). Using landscape-scale crown (leaves and twigs) NSC concentration measurements in three foundation tree species (Populus tremuloides, Pinus edulis, Juniperus osteosperma), we evaluated in situ, seasonal variation in NSC responses to moisture stress on three timescales: short-term (via predawn water potential), seasonal (via leaf δ13C) and annual (via current year’s ring width index). Crown NSC responses to moisture stress appeared to depend on hydraulic strategy, where J. osteosperma appears to regulate osmotic potentials (via higher sugar concentrations), P. edulis NSC responses suggest respiratory depletion and P. tremuloides responses were consistent with direct sink limitations. We also show that overly simplistic models can mask seasonal and tissue variation in NSC responses, as well as strong interactions among moisture stress at different timescales. In general, our results suggest large seasonal variation in crown NSC concentrations reflecting the multiple cofunctions of NSCs in plant tissues, including storage, growth and osmotic regulation of hydraulically vulnerable leaves. We emphasize that crown NSC pool size cannot be viewed as a simple physiological metric of stress; in situ NSC dynamics are complex, varying temporally, across species, among NSC fractions and among tissue types.</span>

<span>The diversity patterns of macroorganisms (i.e., plants) among different habitats have been well documented, however, those of microorganisms (i.e., fungi) as well as the relationships between them are still unclear. Here, we tested whether and to what degree fungal diversity was related to habitat types and compared diversity patterns of woody plants and soil fungi. We carried out field investigations on soil fungi in different habitat types (i.e., valleys, foothills, hillsides, and hilltops) in a 25-ha karst broadleaf forest in Southwest China. The tree richness, Shannon index, and Simpson index significantly increased from valleys to hilltops. While the soil fungal N1 diversity (the exponential Shannon index) marginally increased toward valleys, fungal N0 (richness) and N2 (the inverse Simpson index) diversity exhibited significantly reduced and increased patterns, respectively, from valleys to hilltops. The major fungal functional groups (i.e., EcM, AM, saprotrophic, and pathogenic fungi) showed similar increasing richness patterns in valleys. Moreover, woody plant alpha diversity was an important indicator of fungal functional groups except for EcM and AM fungi. In addition, woody plants increased in species turnover rate (βSIM) from valleys to hilltops, while fungal species had a concave distribution. The patterns of nestedness (βSNE) for tree species decreased from valleys to hilltops, while the opposite was true for soil fungal species. Our findings indicated that the diversity patterns of woody plants and fungi were inconsistent among habitat types, and the relationships between fungal and woody plant communities depended on habitat types in the karst forest.</span>

<span>Elevated atmospheric CO2 (eCO2) generally increases carbon input in rice paddy soils and stimulates the growth of methane-producing microorganisms. Therefore, eCO2 is widely expected to increase methane (CH4) emissions from rice agriculture, a major source of anthropogenic CH4. Agricultural practices strongly affect CH4 emissions from rice paddies as well, but whether these practices modulate effects of eCO2 is unclear. Here we show, by combining a series of experiments and meta-analyses, that whereas eCO2 strongly increased CH4 emissions from paddies without straw incorporation, it tended to reduce CH4 emissions from paddy soils with straw incorporation. Our experiments also identified the microbial processes underlying these results: eCO2 increased methane-consuming microorganisms more strongly in soils with straw incorporation than in soils without straw, with the opposite pattern for methane-producing microorganisms. Accounting for the interaction between CO2 and straw management, we estimate that eCO2 increases global CH4 emissions from rice paddies by 3.7%, an order of magnitude lower than previous estimates. Our results suggest that the effect of eCO2 on CH4 emissions from rice paddies is smaller than previously thought and underline the need for judicious agricultural management to curb future CH4 emissions.</span>

<span>The impacts of climate change and extreme weather events (e.g. frost-, heat-, drought-, and heavy rainfall events) on the continuous phenological development over the entire seasonal cycle remained poorly understood. Previous studies mainly focused on modeling key phenological transition dates (e.g. discrete timing of spring bud-break and fall senescence) based on aggregated climate variables (e.g. mean temperature, growing-degree days). We developed and evaluated a Bayesian Hierarchical Space-Time model for Land Surface Phenology (BHST-LSP) to synthesize remotely sensed vegetation greenness with climate covariates at a daily temporal scale from 1981 to 2014 across the entire conterminous United States. The BHST-LSP model incorporated both temporal and spatial information and exhibited high predictive power in simulating daily phenological development with an overall out-of-sample R2 of 0.80 ± 0.17 and 0.72 ± 0.20 for spring and fall phenology, respectively. The overall out-of-sample normalized root mean square errors were 9.3% ± 6.1% and 9.9% ± 5.2% between the observed and predicted vegetation greenness for spring and fall phenology, respectively. We found that a fast increase of temperature can accelerate the speed of spring green-up while a slow decrease of temperature can lead to a decelerated fall brown-down. Increasing accumulated precipitation can benefit daily phenological development over an entire growing season, while extreme rainfall events can have the opposite effects. More frequent frost events could slow spring leaf expansion and accelerate fall leaf senescence. Impacts of extreme heat events were complex and depended on water availability. Cropland in the Midwest as well as evergreen needleleaf forest along the coastal regions showed relatively strong resistance to drought events compared to other land cover types. The BHST-LSP model can be used to forecast vegetation phenology given future climate projection, thus providing valuable information for adopting climate change adaptation and mitigation measures.</span>

<span>Permafrost thaw is typically measured with active layer thickness, or the maximum seasonal thaw measured from the ground surface. However, previous work has shown that this measurement alone fails to account for ground subsidence and therefore underestimates permafrost thaw. To determine the impact of subsidence on observed permafrost thaw and thawed soil carbon stocks, we quantified subsidence using high-accuracy GPS and identified its environmental drivers in a permafrost warming experiment near the southern limit of permafrost in Alaska. With permafrost temperatures near 0°C, 10.8 cm of subsidence was observed in control plots over 9 years. Experimental air and soil warming increased subsidence by five times and created inundated microsites. Across treatments, ice and soil loss drove 85?91% and 9?15% of subsidence, respectively. Accounting for subsidence, permafrost thawed between 19% (control) and 49% (warming) deeper than active layer thickness indicated, and the amount of newly thawed carbon within the active layer was between 37% (control) and 113% (warming) greater. As additional carbon thaws as the active layer deepens, carbon fluxes to the atmosphere and lateral transport of carbon in groundwater could increase. The magnitude of this impact is uncertain at the landscape scale, though, due to limited subsidence measurements. Therefore, to determine the full extent of permafrost thaw across the circumpolar region and its feedback on the carbon cycle, it is necessary to quantify subsidence more broadly across the circumpolar region.</span>

<span>Root endophytes are a promising tool for increasing plant growth, but it is unclear whether they perform consistently across plant hosts. We characterized the blue grama (Bouteloua gracilis) root microbiome using two sequencing methods, quantified the effects of root endophytes in the original host (blue grama) and an agricultural recipient, corn (Zea mays), under drought and well-watered conditions and examined in vitro mechanisms for plant growth promotion. 16S rRNA amplicon sequencing revealed that the blue grama root microbiome was similar across an elevation gradient, with the exception of four genera. Culturing and Sanger sequencing revealed eight unique endophytes belonging to the genera Bacillus, Lysinibacillus and Pseudomonas. All eight endophytes colonized corn roots, but had opposing effects on aboveground and belowground biomass in each plant species: they increased blue grama shoot mass by 45% (19) (mean +/− SE) while decreasing corn shoot mass by 10% (19), and increased corn root:shoot by 44% (7), while decreasing blue grama root:shoot by 17% (7). Furthermore, contrary to our expectations, endophytes had stronger effects on plant growth under well-watered conditions rather than drought conditions. Collectively, these results suggest that ecological features, including host identity, bacterial traits, climate conditions and morphological outcomes, should be carefully considered in the design and implementation of agricultural inocula.</span>

<span>Water and CO2 flux responses (e.g., evapotranspiration [ET] and net ecosystem exchange [NEE]) to environmental conditions can provide insights into how climate change will affect the terrestrial water and carbon budgets, especially in sensitive semiarid ecosystems. Here, we evaluated sensitivity of daily ET and NEE to current and antecedent (past) environment conditions, including atmospheric (vapor pressure deficit [VPD] and air temperature [Tair]) and moisture (precipitation and soil water) drivers. We focused on two common southwestern U.S. (?Southwest?) biomes: pinyon-juniper woodland (Pinus edulis, Juniperus monosperma) and ponderosa pine forest (Pinus ponderosa). Due to differences in aridity, rooting patterns, and plant physiological strategies (stomatal and hydraulic traits), we expected ET and NEE in these ecosystems to respond differently to atmospheric and moisture drivers, with longer response timescales in the drier pinyon-juniper woodland. Net sensitivity to drivers varied temporally in both ecosystems, reflecting the integrated influence of interacting drivers and antecedent precipitation patterns. NEE sensitivity to VPD and soil moisture (and ET sensitivity to deep soil moisture [Sdeep]) was higher in the ponderosa forest. ET and NEE in both ecosystems responded almost instantaneously to Tair, VPD, and shallow soil moisture (Sshall), and increases in any of these drivers weakened the carbon sink and enhanced water loss. Conversely, Sdeep and precipitation influenced ET and NEE over longer timescales (days to months, respectively), and higher Sdeep enhanced the carbon sink. As climate changes, these results suggest hotter and drier conditions will weaken the carbon sink and exacerbate water loss from Southwest pinyon-juniper and ponderosa ecosystems.</span>

<span>The magnitude of carbon (C) loss to the atmosphere via microbial decomposition is a function of the amount of C stored in soils, the quality of the organic matter, and physical, chemical, and biological factors that comprise the environment for decomposition. The decomposability of C is commonly assessed by laboratory soil incubation studies that measure greenhouse gases mineralized from soils under controlled conditions. Here, we introduce the Soil Incubation Database (SIDb) version 1.0, a compilation of time series data from incubations, structured into a new, publicly available, open-access database of C flux (carbon dioxide, </span><span class="inline-formula">CO₂</span><span>, or methane, </span><span class="inline-formula">CH₄</span><span>). In addition, the SIDb project also provides a platform for the development of tools for reading and analysis of incubation data as well as documentation for future use and development. In addition to introducing SIDb, we provide reporting guidance for database entry and the required variables that incubation studies need at minimum to be included in SIDb. A key application of this synthesis effort is to better characterize soil C processes in Earth system models, which will in turn reduce our uncertainty in predicting the response of soil C decomposition to a changing climate. We demonstrate a framework to fit curves to a number of incubation studies from diverse ecosystems, depths, and organic matter content using a built-in model development module that integrates SIDb with the existing SoilR package to estimate soil C pools from time series data. The database will help bridge the gap between point location measurements, which are commonly used in incubation studies, and global remote-sensed data or data products derived from models aimed at assessing global-scale rates of decomposition and C turnover. The SIDb version 1.0 is archived and publicly available at </span><a href="https://doi.org/10.5281/zenodo.3871263">https://doi.org/10.5281/zenodo.3871263</a><span> (Sierra et al., 2020), and the database is managed under a version-controlled system and centrally stored in GitHub (</span><span class="uri"><a href="https://github.com/SoilBGC-Datashare/sidb" target="_blank" rel="noopener noreferrer">https://github.com/SoilBGC-Datashare/sidb</a></span><span>, last access: 26 June 2020).</span>

<span>Terrestrial vegetation removes CO2 from the atmosphere; an important climate regulation service that slows global warming. This 119 Pg C per annum transfer of CO2 into plants—gross primary productivity (GPP)—is the largest land carbon flux globally. While understanding past and anticipated future GPP changes is necessary to support carbon management, the factors driving long-term changes in GPP are largely unknown. Here we show that 1901 to 2010 changes in GPP have been dominated by anthropogenic activity. Our dual constraint attribution approach provides three insights into the spatiotemporal patterns of GPP change. First, anthropogenic controls on GPP change have increased from 57% (1901 decade) to 94% (2001 decade) of the vegetated land surface. Second, CO2 fertilization and nitro  gen deposition are the most important drivers of change, 19.8 and 11.1 Pg C per annum (2001 decade) respectively, especially in the tropics and industrialized areas since the 1970’s. Third, changes in climate have functioned as fertilization to enhance GPP (1.4 Pg C per annum in the 2001 decade). These findings suggest that, from a land carbon balance perspective, the Anthropocene began over 100 years ago and that global change drivers have allowed GPP uptake to keep pace with anthropogenic emissions.</span>

<span>Evergreen conifer forests are the most prevalent land cover type in North America. Seasonal changes in the color of evergreen forest canopies have been documented with near-surface remote sensing, but the physiological mechanisms underlying these changes, and the implications for photosynthetic uptake, have not been fully elucidated. Here, we integrate on-the-ground phenological observations, leaf-level physiological measurements, near surface hyperspectral remote sensing and digital camera imagery, tower-based CO2 flux measurements, and a predictive model to simulate seasonal canopy color dynamics. We show that seasonal changes in canopy color occur independently of new leaf production, but track changes in chlorophyll fluorescence, the photochemical reflectance index, and leaf pigmentation. We demonstrate that at winter-dormant sites, seasonal changes in canopy color can be used to predict the onset of canopy-level photosynthesis in spring, and its cessation in autumn. Finally, we parameterize a simple temperature-based model to predict the seasonal cycle of canopy greenness, and we show that the model successfully simulates interannual variation in the timing of changes in canopy color. These results provide mechanistic insight into the factors driving seasonal changes in evergreen canopy color and provide opportunities to monitor and model seasonal variation in photosynthetic activity using color-based vegetation indices.</span>

<span>Rising temperatures with increased drought pose two challenges for management of future biodiversity. First, are the most vulnerable species concentrated in specific regions and habitats? Second, where can landscape heterogeneity potentially mitigate impacts? We conducted a comprehensive trait analysis of forest plots spanning the eastern United States to quantify how resource-acquisitive species respond to moisture-soil-climate interactions. We found that resource-acquisitive species, including nutrient-acquisitive and moisture-acquisitive species, respond disproportionately to environmental gradients, and their response is largely explained by soil variation. We showed that the strong boundary of resource-acquisitive species occurs near the last glacial limit, highlighting one of the clearest indicators of soil controls. Although local soil moisture may reduce drought-induced stress for moisture-acquisitive species, nutrient-acquisitive species remain vulnerable on wet soils in dry climates. The results suggest that theories explaining species distributions should devote close attention to the combination of local drainage and soil type.</span>

<span>Despite abounding evidence that leaf litter traits can predict decomposition rate, the way these traits influence trophic efficiency and element transfer to higher trophic levels is not resolved. Here, we used litter labeled with 13C and 15N stable isotopes to trace fluxes of litter C and N from four leaf types to freshwater invertebrate communities. We measured absolute (mg C or N) and relative assimilation (percentage of litter C or N incorporated into invertebrate biomass relative to C and N lost during decomposition). Four patterns emerged: (1) Invertebrate communities assimilated more C and N from slowly decomposing litter than communities feeding on rapidly decomposing litter; (2) absolute assimilation of both C and N in leaf packs was positively correlated with the relative biomass of invertebrate taxa in leaf packs; (3) Chironomidae larvae, which colonize packs in the early decomposition stages, assimilated the most C and N by the end of the 35-day experiment; and (4) most taxa, spanning five functional feeding groups (collector–gatherers, shredders, collector–filterers, scrapers, and predators), showed similar patterns in both absolute and relative assimilation across leaf types. These results challenge traditional views of litter quality by demonstrating that trophic efficiency is negatively associated with decomposition rate across these four leaf types.</span>

<span>Quantitative stable isotope probing (qSIP) estimates the degree of incorporation of an isotope tracer into nucleic acids of metabolically active organisms and can be applied to microorganisms growing in complex communities, such as the microbiomes of soil or water. As such, qSIP has the potential to link microbial biodiversity and biogeochemistry. As with any technique involving quantitative estimation, qSIP involves measurement error; a more complete understanding of error, precision and statistical power will aid in the design of qSIP experiments and interpretation of qSIP data. We used several existing qSIP datasets of microbial communities found in soil and water to evaluate how variance in the estimate of isotope incorporation depends on organism abundance and on the resolution of the density fractionation scheme. We also assessed statistical power for replicated qSIP studies, and sensitivity and specificity for unreplicated designs. We found that variance declines as taxon abundance increases. Increasing the number of density fractions reduces variance, although the benefit of added fractions declines as the number of fractions increases. Specifically, nine fractions appear to be a reasonable tradeoff between cost and precision for most qSIP applications. Increasing replication improves power and reduces the minimum detectable threshold for inferring isotope uptake to 5 atom%. Finally, we provide evidence for the importance of internal standards to calibrate the %GC to mean weighted density regression per sample. These results should benefit those designing future SIP experiments, and provide a reference for metagenomic SIP applications where financial and computational limitations constrain experimental scope.Importance One of the biggest challenges in microbial ecology is correlating the identity of microorganisms with the roles they fulfill in natural environmental systems. Studies of microbes in pure culture reveal much about genomic content and potential functions, but may not reflect an organism’s activity within its natural community. Culture-independent studies supply a community-wide view of composition and function in the context of community interactions, but fail to link the two. Quantitative stable isotope probing (qSIP) is a method that can link the identity and function of specific microbes within a naturally occurring community. Here we explore how the resolution of density-gradient fractionation affects the error and precision of qSIP results, how they may be improved via additional replication, and cost-benefit balanced scenarios for SIP experimental design.</span>

<span>The amount of reactive nitrogen has more than doubled in terrestrial ecosystems due to human activities such fertiliser application that is predicted to increase dramatically in coming decades. We conducted a 3-year experiment in a Neotropical savanna in which we determined the effects of increased N deposition on litter decomposition in plots subjected to different levels of N addition (50 kg N ha?1 year?2, 20 kg N ha?1 year?2, or no N addition). For this, we compared the litter decomposition from the bunchgrass Tristachya leiostachya using litter collected from plots with different N addition treatments. Five randomly selected bags of litter from each N addition treatment (origin) were distributed to each plot (destination). We also compared litter nitrogen (N) concentration and indicators of microbial activity (basal respiration, carbon of microbial biomass, metabolic quotient, enzyme activity) in all plots. We found that nitrogen addition influences litter decay, but in idiosyncratic ways that differ between years. In year 1, litter decomposed faster in high-N addition plots than in low-N and control plots, regardless of its origin. In contrast, litter from high-N addition plots decomposing fastest in year 2, regardless of its destination. Finally, there was no effect of either litter origin or destination on the rate of decomposition in year 3. Litter collected in high-N addition plots had a concentration of N 12?17% higher than litter collected in other plots and higher in 2009 than in other years. Four years after the beginning of the fertilisation experiment, concentration and the microbial activity in the soil did not differ between the treatments. Our findings suggest that the levels of N addition predicted for Neotropical savannas can alter litter N concentrations and the process of litter decomposition, but that the direction and magnitude of these changes may be challenging to predict since that precipitation can influence the mechanisms regulating decomposition in the Cerrado.</span>

<span>Moss-associated N2 fixation provides a substantial but heterogeneous input of new N to nutrient-limited ecosystems at high latitudes. In spite of the broad diversity of mosses found in boreal and Arctic ecosystems, the extent to which host moss identity drives variation in N2 fixation rates remains largely undetermined. We used 15N2 incubations to quantify the fixation rates associated with 34 moss species from 24 sites ranging from 60° to 68° N in Alaska, USA. Remarkably, all sampled moss genera fixed N2, including well-studied feather and peat mosses and genera such as Tomentypnum, Dicranum, and Polytrichum. The total moss-associated N2 fixation rates ranged from almost zero to 3.2 mg N m−2 d−1, with an average of 0.8 mg N m−2 d−1, based on abundance-weighted averages of all mosses summed for each site. Random forest models indicated that moss taxonomic family was a better predictor of rate variation across Alaska than any of the measured environmental factors, including site, pH, tree density, and mean annual precipitation and temperature. Consistent with this finding, mixed models showed that trends in N2 fixation rates among moss genera were consistent across biomes. We also found “hotspots” of high fixation rates in one-fourth of sampled sites. Our results demonstrated the importance of moss identity in influencing N2 fixation rates. This in turn indicates the potential utility of moss identity when making ecosystem N input predictions and exploring other sources of process rate variation.</span>

<span>In a warmer world, microbial decomposition of previously frozen organic carbon (C) is one of the most likely positive climate feedbacks of permafrost regions to the atmosphere. However, mechanistic understanding of microbial mediation on chemically recalcitrant C instability is limited; thus, it is crucial to identify and evaluate active decomposers of chemically recalcitrant C, which is essential for predicting C-cycle feedbacks and their relative strength of influence on climate change. Using stable isotope probing of the active layer of Arctic tundra soils after depleting soil labile C through a 975-day laboratory incubation, the identity of microbial decomposers of lignin and, their responses to warming were revealed.</span>

<span>An amendment to this paper has been published and can be accessed via a link at the top of the paper.</span>

<span>The permafrost zone is expected to be a substantial carbon source to the atmosphere, yet large-scale models currently only simulate gradual changes in seasonally thawed soil. Abrupt thaw will probably occur in &lt;20% of the permafrost zone but could affect half of permafrost carbon through collapsing ground, rapid erosion and landslides. Here, we synthesize the best available information and develop inventory models to simulate abrupt thaw impacts on permafrost carbon balance. Emissions across 2.5 million km2 of abrupt thaw could provide a similar climate feedback as gradual thaw emissions from the entire 18 million km2 permafrost region under the warming projection of Representative Concentration Pathway 8.5. While models forecast that gradual thaw may lead to net ecosystem carbon uptake under projections of Representative Concentration Pathway 4.5, abrupt thaw emissions are likely to offset this potential carbon sink. Active hillslope erosional features will occupy 3% of abrupt thaw terrain by 2300 but emit one-third of abrupt thaw carbon losses. Thaw lakes and wetlands are methane hot spots but their carbon release is partially offset by slowly regrowing vegetation. After considering abrupt thaw stabilization, lake drainage and soil carbon uptake by vegetation regrowth, we conclude that models considering only gradual permafrost thaw are substantially underestimating carbon emissions from thawing permafrost.</span>

<span>Terrestrial animal communities are largely shaped by vegetation and climate. With climate also shaping vegetation, can we attribute animal patterns solely to climate? Our study observes ant community changes along climatic gradients (i.e., elevational gradients) within different habitat types (i.e., open and forest) on the Colorado Plateau in the southwestern United States. We sampled ants and vegetation along two elevational gradients spanning 1,132 m with average annual temperature and precipitation differences of 5.7°C and 645mm, respectively. We used regression analyses and structural equation modeling to compare the explanatory powers and effect sizes of climate and vegetation variables on ants. Climate variables had the strongest correlations and the largest effect sizes on ant communities, while vegetation composition, richness, and primary productivity had relatively small effects. Precipitation was the strongest predictor for most ant community metrics. Ant richness and abundance had a negative relationship with precipitation in forested habitats, and positive in open habitats. Our results show strong direct climate effects on ants with little or no effects of vegetation composition or primary productivity, but contrasting patterns between vegetation type (i.e., forested vs. open) with precipitation. This indicates vegetation structure can modulate climate responses of ant communities. Our study demonstrates climate-animal relationships may vary among vegetation types which can impact both findings from elevational studies and how communities will react to changes in climate.</span>

<span>In this work we define a spatial concordance coefficient for second-order stationary processes. This problem has been widely addressed in a non-spatial context, but here we consider a coefficient that for a fixed spatial lag allows one to compare two spatial sequences along a 45°line. The proposed coefficient was explored for the bivariate Matérn and Wendland covariance functions. The asymptotic normality of a sample version of the spatial concordance coefficient for an increasing domain sampling framework was established for the Wendland covariance function. To work with large digital images, we developed a local approach for estimating the concordance that uses local spatial models on non-overlapping windows. Monte Carlo simulations were used to gain additional insights into the asymptotic properties for finite sample sizes. As an illustrative example, we applied this methodology to two similar images of a deciduous forest canopy. The images were recorded with different cameras but similar fields-of-view and within minutes of each other. Our analysis showed that the local approach helped to explain a percentage of the non-spatial concordance and provided additional information about its decay as a function of the spatial lag.</span>

<span>Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf-scale photosynthesis and intrinsic water-use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2-responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]-driven terrestrial carbon sink can appear contradictory. Here we synthesise theory and broad, multi-disciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre-industry. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2-responses are high in comparison with experiments and theory. Plant mortality and soil carbon iCO2-responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.</span>

<span>Increases in fire frequency, extent, and severity are expected to strongly impact the structure and function of boreal forest ecosystems. An important function of the boreal forest is its ability to sequester and store carbon (C). Increasing disturbance from wildfires, emitting large amounts of C to the atmosphere, may create a positive feedback to climate warming. Variation in ecosystem structure and function throughout the boreal forest is important for predicting the effects of climate warming and changing fire regimes on C dynamics. In this study, we compiled data on soil characteristics, stand structure, pre-fire C pools, C loss from fire, and the potential drivers of these C metrics from 527 sites distributed across six ecoregions of North America’s western boreal forests. We assessed structural and functional differences between these fire-prone ecoregions using data from 417 recently burned sites (2004–2015) and estimated ecoregion-specific relationships between soil characteristics and depth from 167 of these sites plus an additional 110 sites (27 burned, 83 unburned). We found that northern boreal ecoregions were generally older, stored and emitted proportionally more belowground than aboveground C, and exhibited lower rates of C accumulation over time than southern ecoregions. We present ecoregion-specific estimates of depth-wise soil characteristics that are important for predicting C combustion from fire. As climate continues to warm and disturbance from wildfires increases, the C dynamics of these fire-prone ecoregions are likely to change with significant implications for the global C cycle and its feedbacks to climate change.</span>

<span>Carbon (C) emissions from wildfires are a key terrestrial–atmosphere interaction that influences global atmospheric composition and climate. Positive feedbacks between climate warming and boreal wildfires are predicted based on top-down controls of fire weather and climate, but C emissions from boreal fires may also depend on bottom-up controls of fuel availability related to edaphic controls and overstory tree composition. Here we synthesized data from 417 field sites spanning six ecoregions in the northwestern North American boreal forest and assessed the network of interactions among potential bottom-up and top-down drivers of C emissions. Our results indicate that C emissions are more strongly driven by fuel availability than by fire weather, highlighting the importance of fine-scale drainage conditions, overstory tree species composition and fuel accumulation rates for predicting total C emissions. By implication, climate change-induced modification of fuels needs to be considered for accurately predicting future C emissions from boreal wildfires.</span>

<span>When multiple metabolic pathways lead to the same product, compound-specific isotope analysis may not provide enough information to quantify the activities of the contributing pathways. Instead, identification of where in the molecule the 13C is incorporated is required. Here we show how knowledge of position-specific 13C incorporation in fatty acids (FA) and FA fragments can be used to quantitatively estimate the fluxes through the central C metabolic network. We developed a method to measure 13C enrichment of FA and FA fragments (ethanoate, propionate) using electron impact GC–MS. We tested the accuracy and repeatability of the measurements using natural abundance and position-specific 13C labelled standards and FA extracted from Bacillus licheniformis and Pseudomonas fluorescens grown with labelled and unlabelled glucose. The molecular ions of FA generally reflected theoretical predictions of mass isotopomer distributions for natural abundance values, but that of the associated FA fragments deviated from expected values, likely associated with McLafferty rearrangements of hydrogen. After correction for naturally occurring isotopes, 13C enrichments of FA and FA fragments showed good agreement with expected isotope composition of FA standards (root mean square error &lt; 0.044 at%; δ13C of ∼ 40‰), natural abundance and labelled glucose. The unsaturated FA extracted from P. fluorescens deviated from expected values likely associated with problems of co-elution and ion suppression and were excluded from analysis. The ratio of glucose-1-13C to glucose-3-13C incorporation into FA fragments was high for B. licheniformis, but low for P. fluorescens. Metabolic flux modelling based on the 13C enrichment of ethanoate and propionate fragments showed that B. licheniformis used Embden-Meyerhof-Parnas and pentose phosphate pathway (66% and 30%, respectively), whereas P. fluorescens utilized Entner-Doudoroff and pentose phosphate pathway (72% and 27%, respectively). FA fragment analysis is therefore a promising tool to study central C metabolic network activities of co-occurring groups of microbes in intact and complex environmental communities.</span>

<span>The effects of invasive plants on soil carbon (C) and nitrogen (N) cycling are widely documented, while the mechanisms of their influences on the microbial ecology of soil remain unknown. Therefore, the objective of this study was to explore variations in soil bacterial communities following plant invasion, and the mechanisms that drive these changes.</span>

<span>Unique soil properties in rhizosphere can affect plant growth and biogeochemical cycles of ecosystems. While rhizosphere has been widely investigated, little is known about differences in the rhizosphere effect (RE) between co-existing overstory trees and understory shrubs and herbs in forest ecosystems. In this study, we investigated REs on soil chemical properties of overstory trees and understory shrubs and herbs in forest plantations of southern China. Bulk soil and rhizospheres were sampled in April, July and December 2017. Soil pH, nitrate and ammonium nitrogen, dissolved organic carbon, available phosphorus, total carbon, total nitrogen, and total phosphorus were tested. The REs were defined as the ratios of the chemical properties of the rhizospheres to those of the bulk soil. Our results showed that pH was lower and nutrient contents were higher in the plant rhizospheres than the bulk soil. REs were generally larger in trees than understory plants. The REs were larger in July than April and December. Our findings indicated that the RE varied among plant life forms, species and sampling times, emphasizing the functional role of the RE of understory vegetation in subtropical forests.</span>

<span>Rubber powdery mildew caused by the foliar fungi Oidium heveae is one of the main diseases affecting rubber plantations (Hevea brasiliensis) worldwide. It is particularly serious in sub-optimal growing areas, such as Xishuangbanna in SW China. To prevent and control this disease, fungicides causing serious environmental problems are widely used. Strong correlations between the infection level and the temperature variables were reported previously, but they were related to monthly data that did not allow unraveling the patterns during the entire sensitive period. We correlated the infection level of powdery mildew of rubber trees recorded over 2003–2011 with antecedent 365 days daily temperature variables using partial least squares (PLS) regression. Our PLS regression results showed that the infection level of powdery mildew responded differently to the temperature variables of the defoliation and refoliation periods. Further analysis with Kriging interpolation showed that the infection level increased by 20% and 11%, respectively, per 1 °C rise of the daily maximum and mean temperature in the defoliation season, while it decreased by 8% and 10%, respectively, per 1 °C rise of the daily maximum and temperature difference in the refoliation season. This pattern was likely linked to the effects of temperature on leaf phenology. It seems highly possible that the infection level of powdery mildew increases, as increasing trends of maximum temperature and mean temperature during the defoliation continue.</span>

<span>Plant functional traits can be used to predict ecosystem responses to climate gradients, yet precipitation explains very little variation for most traits. Soil water availability directly influences plant water uptake and thus may assist with the improvement of plant trait–water relationships. However, this promise remains poorly realized due to rare tests. Here, we provide the first study that attempts to link climate factors, vertical soil water availability, and community composition at a regional scale. Our study paired field-measured vertical soil available water (0–300 cm) and community functional composition at 46 herbaceous grassland sites along a steep hydrothermal gradient in the Loess Plateau of Central China. Community functional composition was expressed via community-weighted means of eight traits. Structural equation modeling was employed to evaluate the role of vertical soil available water content, controlled by precipitation and air temperature, in affecting plant community-weighted traits. We found that soil available water content at depths of 20–100 cm was typically responsible for mediating the effects of precipitation and air temperature on plant community composition. This emerged as the predominant factor to explain variations in grassland response traits, including leaf area, specific leaf area, and leaf dry matter content. These traits exhibited clear drought-induced shifts along soil desiccation gradients and responded to drier conditions by reducing leaf area/specific leaf area and increasing leaf dry matter content. Our findings rehighlighted soil water availability as the core driver that needs to be considered in the restoration and management of dryland ecosystems.</span>

<span>Large-scale vegetation restoration projects pose threats to water resource security in water-limited regions. Thus, the quantification of how vegetation cover affects soil moisture is of key importance to support effective restoration schemes in drylands. However, the current understanding of such effects remains poor. For this study, an in-situ vegetation-removal experiment was conducted at 36 herbaceous grassland sites having different community compositions and topographical conditions in two adjacent loess watersheds of the Loess Plateau, China. The effects of vegetation cover (vegetation effects) on soil moisture were analyzed across soil profiles (0–180 cm) and two growing seasons. Overall, 13 plant traits and 7 topographic and soil properties were employed to evaluate how community compositions modulated vegetation effects on soil moisture. The results showed that vegetation cover increased soil moisture in the surface layer (0–20 cm) by 6.81% during wet periods (semi-monthly rainfall &gt;30 mm) relative to an in-situ unvegetated control, but primarily induced a decline of soil moisture in the deep soil layer (20–180 cm) by 19.44% across two growing seasons. Redundancy analysis (RDA) and structural equation modeling (SEM) suggested that these vegetation effects on soil moisture were significantly correlated with vegetative height, leaf area, shallow root allocation, and slope gradient. Our study revealed that tall, small-leaved, and shallow-rooted plants on flat topographies were beneficial to soil water retention and replenishment. This implied that current restoration strategies may be significantly improved through the development of optimal communities and diverse terracing measures. Our findings are anticipated to provide effective guidance for soil water conservation, as well as ecosystem rehabilitation in dry and degraded regions.</span>

<span>The traditional view holds that biological nitrogen (N) fixation often peaks in early- or mid-successional ecosystems and declines throughout succession based on the hypothesis that soil N richness and/or phosphorus (P) depletion become disadvantageous to N fixers. This view, however, fails to support the observation that N fixers can remain active in many old-growth forests despite the presence of N-rich and/or P-limiting soils. Here, we found unexpected increases in N fixation rates in the soil, forest floor, and moss throughout three successional forests and along six age-gradient forests in southern China. We further found that the variation in N fixation was controlled by substrate carbon(C) : N and C : (N : P) stoichiometry rather than by substrate N or P. Our findings highlight the utility of ecological stoichiometry in illuminating the mechanisms that couple forest succession and N cycling.</span>

<span>Biological nitrogen (N) fixation plays an important role in terrestrial N cycling and represents a key driver of terrestrial net primary productivity (NPP). Despite the importance of N fixation in terrestrial ecosystems, our knowledge regarding the controls on terrestrial N fixation remains poor. Here, we conducted a meta-analysis (based on 852 observations from 158 studies) of N fixation across three types of ecosystems with different status of disturbance (no management, restoration [previously disturbed], and disturbance [currently disturbed]) and in response to multiple environmental change factors (warming, elevated carbon dioxide [CO2], increased precipitation, increased drought, increased N deposition, and their combinations). We explored the mechanisms underlying the changes in N fixation by examining the variations in soil physicochemical properties (bulk density, texture, moisture, and pH), plant and microbial characteristics (dominant plant species numbers, plant coverage, and soil microbial biomass), and soil resources (total carbon, total N, total phosphorus (P), inorganic N, and inorganic P). Human disturbance inhibited non-symbiotic N fixation but not symbiotic N fixation. Terrestrial N fixation was stimulated by warming (+152.7%), elevated CO2 (+19.6%), and increased precipitation (+73.1%) but inhibited by increased drought (?30.4%), N deposition (?31.0%), and combinations of available multiple environmental change factors (?14.5%), the extents of which varied among biomes and ecosystem compartments. Human disturbance reduced the N fixation responses to environmental change factors, which was associated with the changes in soil physicochemical properties (2%?56%, p &lt; .001) and the declines in plant and microbial characteristics (3%?49%, p ≤ .003) and soil resources (6%?48%, p ≤ .03). Overall, our findings reveal for the first time the effects of multiple environmental change factors on terrestrial N fixation and indicate the role of human disturbance activities in inhibiting N fixation, which can improve our understanding, modeling, and prediction of terrestrial N budgets, NPP, and ecosystem feedbacks under global change scenarios.</span>

<span>Biodiversity on the Earth is changing at an unprecedented rate due to a variety of global change factors (GCFs). However, the effects of GCFs on microbial diversity is unclear despite that soil microorganisms play a critical role in biogeochemical cycling. Here, we synthesize 1235 GCF observations worldwide and show that microbial rare species are more sensitive to GCFs than common species, while GCFs do not always lead to a reduction in microbial diversity. GCFs-induced shifts in microbial alpha diversity can be predominately explained by the changed soil pH. In addition, GCF impacts on soil functionality are explained by microbial community structure and biomass rather than the alpha diversity. Altogether, our findings of GCF impacts on microbial diversity are fundamentally different from previous knowledge for well-studied plant and animal communities, and are crucial to policy-making for the conservation of microbial diversity hotspots under global changes.</span>