Wednesday, August 4, 2010: 9:20 AM
310-311, David L Lawrence Convention Center
Alexia M. Kelley1, Andrew C. Procter2, Richard A. Gill3, Philip A. Fay4, H. Wayne Polley4 and Robert B. Jackson5, (1)Forestry, North Carolina State University, Raleigh, NC, (2)Duke University, Durham, NC, (3)Department of Biology, Brigham Young University, Provo, UT, (4)Grassland, Soil & Water Research Laboratory, USDA, Agricultural Research Service, Temple, TX, (5)School of Earth Sciences, Stanford and Duke universities, Stanford, CA
Background/Question/Methods Increasing atmospheric CO2 has been shown to significantly affect terrestrial ecosystems through increased primary production. This response is thought to be mitigated by changes to the soil microbial community, which can alter nutrient availability in these systems. In this study we examine the effects of a unique field gradient of atmospheric CO2, ranging form 250 ppm to 500 ppm, on soil microbial communities and function in a model grassland system. Within this experimental set-up there are three distinct soils from the following three series: two silty-clay soils, Austin (mollisol) and Houston (vertisol), and a sandy loam, Bastrop (alfisol). Each of these plots was planted with identical grassland communities. To assess how microbial function and communities differed in response to changing atmospheric CO2, we measured extracellular enzyme activity of several enzymes associated with biogeochemical function, as well as fungal-to-bacterial ratios with qPCR, in 2 soil types at several points along the CO2 gradient. These measurements in combination with studies of soil respiration and organic matter decomposition provide insight into how this ecosystem responds to changing CO2 concentrations.
Results/Conclusions
A variety of processes within our model ecosystem respond to the CO2 gradient. Soil respiration tends to increase with CO2 concentration, although the response varies by soil type. To understand the role the microbes have in this response, we found that in some soils, the microbial community shifted towards a higher fungi:bacteria ratio. Microbially-produced enzymes also responded to increase CO2 concentration, with decreased cellulase and glucosidase activity, and decreases increased chitinase activity, indicating a shift in the function of the microbial community response to changing CO2 concentrations. These data demonstrate that changes in CO2 concentrations affect the entire ecosystem, including microbial nutrient cycling.
