COS 20-4
Assessing the relative importance of microbial versus abiotic factors for an ecosystem function: An evaluation of soil respiration rates from three grassland soils reciprocally transplanted with microbial communities

Tuesday, August 12, 2014: 9:00 AM
302/303, Sacramento Convention Center
Charlotte J. Alster, Biology, Colorado State University, Fort Collins, CO
Akihiro Koyama, Biology, Algoma University, Sault Ste. Marie, ON, Canada
Nels G. Johnson, Department of Biology, Colorado State University, Fort Collins, CO
Joe C. von Fischer, Department of Biology, Colorado State University, Fort Collins, CO
Background/Question/Methods

Abiotic factors including soil characteristics shape soil microbial community composition and diversity, which in turn can influence ecosystem functions. However, it is important to understand the relative contributions of microbial community versus abiotic controls on ecosystem functions, such as soil organic matter (SOM) decomposition. This fundamental understanding helps us predict how environmental changes (e.g. warming) affect ecosystem processes. We used three grassland soils and associated soil microbial communities to assess the relative importance between microbial and abiotic factors. Specifically, we used a reciprocal transplant microcosm experiment to examine the effect of soil characteristics, microbial community composition, and temperature on soil respiration. We hypothesized that microbial communities would have the highest relative rates of respiration when transplanted back into soils from which they originated. Respiration was measured at six time points over a period of three months.

Results/Conclusions

We found that microbial inoculum types explained less than 0.05% of the variation in soil respiration rates (p=0.002). The majority of variation in soil respiration rates can be explained by soil type and temperature (p<0.001). However, at the lowest temperature labile C was depleted faster by “home” microbes, especially from the site with the lowest mean annual temperature. At the warmer temperatures, some inoculum types showed higher respiration rates regardless of if it was in its “home” environment. Furthermore, some inoculum sources appeared to exhibit greater temperature sensitivity than others. Our results suggest that functional response of microbial communities are most impacted by current environmental conditions, but that community history can play a subtle role in predicting soil respiration rates.