PS 30-11
Soil microbial population and C and N pools response to simulated conditions of climate change
One of the most widely discussed contributions of soil microorganisms is their role in soil carbon and nitrogen dynamics. Most studies have focused on the effects of individual factorsof climate change on biogeochemical processes and soil microbes. However, there is considerable potential for the additive or antagonistic effects of multiple and interactive climate drivers on soil microorganisms and soil carbon and nitrogen pools. Since both precipitation and N deposition are changing in southern California, we hypothesized that interactions between drought and N addition would be more important drivers of the grassland and the shrubland responses when compared to individual factors alone. We examined soil microbial community and C and N pools responses to interaction between precipitation and N deposition based on an ongoing, multifactor climate change experiment in the Loma Ridge site in Southern California grassland and shrubland. We used the two-step acid hydrolysis procedure with H2SO4as the extractant to determine the labile and recalcitrant C and N pools. Phospholipid fatty acid (PLFA) analysis was used to measure microbial biomass and community composition in the soils. The Shannon index (H′) was calculated from the bacterial lipid biomarkers to estimate soil microbial diversity.
Results/Conclusions
The microbial population density and carbon and nitrogen pools differed significantly (P<0.0001) by ecosystem type (grass- compared to shrub-land) but followed parallel responses to the climate change manipulations. In both ecosystems, microbial population and diversity declined significantly (P<0.05) under drought+N addition treatment. The results show more severe shrubland than grassland’s C and N pools responses to climate change scenarios. Mesocosm plots simulating N deposition contained significantly (P<0.05) more labile pools of carbon and nitrogen, which declined substantially in plots simulating drought conditions. In conclusion, the interaction of N deposition and drought manipulations influenced the response of soil microbial community abundances and diversity in both grassland and shrubland.