Publications

Soil organic carbon (SOC) is the largest reservoir of organic carbon in the terrestrial biosphere. Though the influence of increasing atmospheric CO₂ on net primary productivity, on the flow of newly fixed carbon belowground, and on the quality of new plant litter in ecosystems has been examined, indirect effects of increased CO₂ on breakdown of large SOC pools already in ecosystems are not well understood. We found that exposure of California grassland communities to elevated CO₂ retarded decomposition of older SOC when mineral nutrients were abundant, thus increasing the turnover time of SOC already in the system. Under elevated CO₂, soil microorganisms appeared to shift from consuming older SOC to utilizing easily degraded rhizodeposits derived from increased root biomass. In contrast to this increased retention of stabilized older SOC under elevated CO₂, movement of newly fixed carbon from roots to stabilized SOC pools was retarded; though root biomass increased under elevated CO₂, new carbon in mineral-bound pools decreased. These contrasting effects of elevated CO₂ on dynamics of old and new soil carbon pools contribute to a new soil carbon equilibrium that could profoundly affect long-term net carbon movement between terrestrial ecosystems and the atmosphere.

Humans are altering the environment in many ways. While local environmental damage (landfills, oil spills, urban smog) is still prevalent, we now also realize that human activities are altering the Earth System as a whole, that our environmental crisis has become truly global.

The results of a 3-yr study on the effects of elevated CO₂ on soil N and P, soil pCO₂, and calculated CO₂ efflux in a fire-regenerated Florida scrub oak ecosystem are summarized. We hypothesized that elevated CO₂ would cause (i) increases in soil pCO₂ and soil respiration and (ii) reduced levels of soil-available N and P. The effects of elevated CO₂ on soil N availability differed according to the method used. Results of resin lysimeter collections and anion exchange membrane tests in the field showed reduced NO⁻ ₃ in soils in Years 1 and 3. On the other hand, re-analysis of homogenized, buried soil bags after 1 yr suggested a relative increase in N availability (lower C to N ratio) under elevated CO₂ In the case of P, the buried bags and membranes suggested a negative effect of CO₂ on P during the first year; this faded over time, however, as P availability declined overall, probably in response to P uptake. Elevated CO₂ had no effect on soil pCO₂ or calculated soil respiration at any time, further suggesting that plant rather than microbial uptake was the primary factor responsible for the observed changes in N and P availability with elevated CO₂

This paper presents reviews on: the nutrient responses to elevated CO 2 in open-top chamber and their potential effects on stand level cycling through logic and simulation modelling; and the data from free-air CO 2 enrichment (FACE) experiments.

The functioning of" plants in terrestrial ecosystems must satisfy different constraints imposed by the physical environment. The prevention of embolism and conservation of internal water constrain stomatal behavior and leaf area indices that plants may sustain. Plant height and canopy structure are controlled by water and nutrients through carbon allocation between roots and leaves.