Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO2

Carbon dioxide is the main greenhouse gas inducing climate change. Increased global CO₂ emissions, estimated at 8.4 Pg C yr⁻¹ at present, have accelerated from 1% yr⁻¹during 1990–1999 to 2.5% yr⁻¹ during 2000–2009 (ref. 1). The carbon balance of terrestrial ecosystems is the greatest unknown in the global C budget because the actual magnitude, location and causes of terrestrial sinks are uncertain²; estimates of terrestrial C uptake, therefore, are often based on the residuals between direct measurements of the atmospheric sink and well-constrained models of ocean uptake of CO₂ (ref. 3). Here we report significant terrestrial C accumulation caused by CO₂ enhancement to net ecosystem productivity in an intact, undisturbed arid ecosystem^{4, 5, 6, 7, 8} following ten years of exposure to elevated atmospheric CO₂. Results provide direct evidence that CO₂fertilization substantially increases ecosystem C storage and that arid ecosystems are significant, previously unrecognized, sinks for atmospheric CO₂ that must be accounted for in efforts to constrain terrestrial and global C cycles.

Read Publication

Authors:Evans RD Koyama A Sonderegger DL Charlet TN Newingham BA Fenstermaker LF Harlow B Jin VL Ogle K Smith SD Nowak RS

Temperature is a primary driver of microbial community composition and taxonomic diversity; however, it is unclear to what extent temperature affects characteristics of central carbon metabolic pathways (CCMPs). In this study, 16S rRNA gene amplicon and metagenome sequencing were combined with 13C-labeled metabolite probing of the CCMPs to assess community carbon metabolism along a temperature gradient (60-95 °C) in Great Boiling Spring, NV. 16S rRNA gene amplicon diversity was inversely proportional to temperature, and Archaea were dominant at higher temperatures. Metagenomes spanning the temperature gradient hosted abundant CCMPs genes and many individual metagenome-assembled genomes had complete pathways. In contrast, genes encoding cellulosomes and some others involved in plant matter degradation and most for photosynthesis and were absent at higher temperatures. In situ 13C-CO2 production from labeled isotopomer pairs of glucose, pyruvate, and acetate suggested lower relative oxidative pentose phosphate pathway activity and/or fermentation at 60°C, and a stable or decreased maintenance energy demand at higher temperatures. Catabolism of 13C-labeled citrate, succinate, L-alanine, L-serine, and L-cysteine was observed at 85°C, demonstrating broad heterotrophic activity. Together, these results suggest that temperature-driven losses in biodiversity in geothermal systems may not alter CCMP function or maintenance energy demands at a community level.

Boreal forests are facing profound changes in their growth environment, including warming-induced water deficits, extended growing seasons, accelerated snowmelt, and permafrost thaw. The influence of warming on trees varies regionally, but in most boreal forests studied to date, tree growth has been found to be negatively affected by increasing temperatures. Here, we used a network of Pinus sylvestris tree-ring collections spanning a wide climate gradient the southern end of the boreal forest in Asia to assess their response to climate change for the period 1958?2014. Contrary to findings in other boreal regions, we found that previously negative effects of temperature on tree growth turned positive in the northern portion of the study network after the onset of rapid warming. Trees in the drier portion did not show this reversal in their climatic response during the period of rapid warming. Abundant water availability during the growing season, particularly in the early to mid-growing season (May?July), is key to the reversal of tree sensitivity to climate. Advancement in the onset of growth appears to allow trees to take advantage of snowmelt water, such that tree growth increases with increasing temperatures during the rapidly warming period. The region's monsoonal climate delivers limited precipitation during the early growing season, and thus snowmelt likely covers the water deficit so trees are less stressed from the onset of earlier growth. Our results indicate that the growth response of P. sylvestris to increasing temperatures strongly related to increased early season water availability. Hence, boreal forests with sufficient water available during crucial parts of the growing season might be more able to withstand or even increase growth during periods of rising temperatures. We suspect that other regions of the boreal forest may be affected by similar dynamics.