How do differences in climate, soil chemical and physical characteristics, and microbial abundance influence soil microbial respiration? At present, our answer is incomplete due to the fact that our knowledge is drawn from disparate studies using differing methods to examine soil from a small number of ecosystem types per study. These studies yield information on decomposers within very narrow ranges of site and soil characteristics compared to the full range that exists, making patterns in abundance and activity difficult to determine.

To better identify patterns we measured microbial respiration in 84 unique soils collected from a variety of long term experimental sites from across North America and the islands of Hawaii and Puerto Rico. We incubated soils for 50 days at constant temperature and moisture to eliminate the influence of these proximal drivers. We compared microbial respiration to soil chemical and physical properties, microbial biomass, and site properties such as vegetation type, mean annual precipitation (MAP), and mean annual temperature (MAT).

Results/Conclusions

We know that climate affects soil characteristics, and that these in turn likely affect decomposers. By using structural equation modeling we were able to test conceptual models of how these drivers might interact. Our resulting model indicates that MAT has a negative effect and MAP has a positive effect on soil organic C pool size (R² = 0.49). Soil organic C, in turn, has a very strong positive influence on microbial biomass (R² = 0.62). Microbial biomass has a direct positive effect on microbial respiration, while climate and organic C affect respiration as mediated by microbial biomass. Clay content has a direct negative impact on the rate of microbial respiration, which is likely due to its influence on substrate supply. With the indirect effects of MAT, MAP, and soil organic C, and the direct influence of microbial biomass and clay content, we are able to explain 78% of the variance in microbial respiration. This model thus gives improved mechanistic insight for improving the conceptual underpinnings of simulation models of microbial respiration.