PARENT SESSION
Oral Session # 66: Ecological Studies at Biosphere II.
Presiding: ML Martinez Vazquez
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 104.

Effects of elevated atmospheric CO₂ on soil microbes in the Intensive Forestry Biome of Biosphere2.

Dane, Laura^*,1, Lipson, David¹, Strahm, Spring¹, Wilson, Richard¹, Murthy, Ramesh², Barron-Gafford, Greg², ¹ Department of Biology, San Diego, CA² Columbia University, Oracle, AZ

ABSTRACT- We studied microbiological properties of soils from three atmospheric CO₂ treatments (400, 800, and 1200 ppm) at the Intensive Forestry Biome of Biosphere2 research center. We measured substrate induced respiration (SIR), enzymatic activities, and microbial biomass (by fumigation-extraction and microscopy). There was high spatial variability within the CO₂ treatments for most of the variables measured. Microbial biomass carbon (C), bacterial numbers, and glucose SIR all tended to increase with increasing CO₂ concentration. This trend was significant for glucose SIR (P=0.04) and was marginally significant for microbial biomass C (P=0.075). The community may also be functionally different between CO₂ treatments; the proportion of the the microbial community that degraded various substrates varied significantly. The ratio of glycine SIR to glutamate SIR was lowest in the 800 ppm treatment (P=0.02), whereas the ratio of salicylate SIR to glucose SIR was highest in the 800 ppm treatment (P=0.04). These data indicate that the microbial community changes nonlinearly in response to CO₂, with some effects being more pronounced at intermediate levels of CO₂. We attempted to explain spatial variation in soil microbial properties by comparing soils collected from the north, middle and south portions of the plots, and by measuring soil organic matter (SOM) in each soil sample. SOM showed a marginally significant increase with increasing CO₂ (P=0.065), possibly indicating increased plant root production. However, unlike most natural ecosystems, correlations between SOM and soil microbial properties were generally weak and non-significant. The middle portion of the plots showed some marginally significant differences from the north and south ends in SIR of salicylate (0.077), glucose (0.044) and glycine (0.065), and had somewhat higher moisture contents (P=0.078). We conclude that there are differences in microbial biomass and activity resulting from the CO₂ treatments, but that spatial variability must be addressed in further studies.

Key words: global change, microbial community, elevated carbon dioxide