Multiple Climate Change Factors Interact to Alter Soil Microbial Community Structure in an Old-Field Ecosystem

Climate change has the potential to alter both the composition and function of a soil's microbial community, and interactions among climate change factors may alter soil communities in ways that are not possible to predict from experiments based on a single factor. This study evaluated the direct and interactive effects of three climate change factors—elevated CO₂, altered amounts of precipitation, and elevated air temperature—on soil microbial communities from an old-field climate change experiment being conducted at Oak Ridge, TN. Soil microbial community composition and biomass were determined by phospholipid fatty acid (PLFA) and neutral lipid fatty acid composition. We found that the interactive effects of precipitation and temperature treatments, as well as the interactive effects of precipitation and CO₂ treatments, had significant impacts on microbial community composition. We found that total soil PLFA concentration, a measure of microbial biomass, was greater in the low-precipitation treatments, especially when low precipitation was combined with ambient CO₂ concentrations or ambient temperature. Ordination analysis indicated that temperature was the most significant predictor of shifts in the soil microbial community composition, explaining approximately 12% of the variance in relative abundance of PLFA biomarkers. The elevated-temperature treatment increased the abundance of Firmicutes (low-guanine–cytosine Gram positive) and decreased the abundance of Gram-negative bacteria. Elevated temperature also reduced the abundance of the arbuscular mycorrhizal fungi PLFA biomarker 16:1ω5c and saprophytic fungal PLFA biomarker 18:2ω6,9. Overall, our data indicate that the interactions among climate change factors alter the composition of soil microbial communities in old-field ecosystems, suggesting potential for changes in microbial community function under predicted future climate conditions.