Soil microbes are involved in a wide variety of soil functions, including soil carbon and nitrogen cycling. Until recently, it was assumed that soil microbial community structure was unimportant for ecosystem functioning, partly because of the assumption that all microbes are everywhere and that their communities contain a high degree of functional redundancy. However, evidence is mounting that soil microbial community structure can influence ecosystem functioning. What remains uncertain is how important they are relative to other factors, such as climate, land use and management. We test their relative role in driving multiple ecosystem functions related to C and nutrient cycling in two studies. The first takes a broad scale approach and assesses the role of soil microbes across five land use types ranging from perennial cropping to grassland to forest. The second looks at the role of soil microbes in driving functions compared to plant species composition and nitrogen fertiliser addition at a single grassland site.
Results/Conclusions
Measures of soil microbial community structure (including microbial biomass, and metrics based on molecular analyses) were often correlated with ecosystem functions and these relationships were generally in the expected direction. Preliminary analysis indicated that the relative role of soil microbes in driving ecosystem functioning is context-dependent. In the first study across land use types, soil microbial community structure was the only variable that drove the response of soil respiration to drying, but it did not appear to play a strong role in determining functions under static conditions. In the second study at the single grassland site, the microbial community tended to have a stronger influence than nitrogen fertiliser addition, but a smaller impact than plant species composition. Overall, our results show that soil microbial community composition does play a role in driving soil functions, but that the relative importance of these effects vary with the type of function measured and context.