A Method for Determining Community Level Physiological Profiles of Organic Soil Horizons

Community level physiological profiles (CLPPs) have been widely used to assess microbial community diversity in soils. Refinement of techniques to determine soil CLPP eventually led to the development of the MicroResp technique. This technique avoids many of the pitfalls of earlier methods by using a whole-soil approach coupled with the convenience of microplates. However, issues related to soil pretreatment (primarily sieving) can arise when using the standard MicroResp method to determine the CLPPs of forest floors. Here, we developed a modified multiple substrate induced respiration (multi-SIR) method that lessens the effects of pretreatment by using a larger soil volume in custom 24-well deep-well plates. Microbial community indices including catabolic evenness (E) and CLPP were determined on a range of forest soils using both the standard MicroResp and our modified multi-SIR method. The modified method reduced the variation among the triplicate substrate wells and displayed a wider range of E among the soils measured. Additionally, using multivariate nonmetric multidimensional scaling (NMDS) as well as cluster analysis, we found that the modified method was able to better detect differences in soil CLPPs. The standard MicroResp method remains a valuable technique for many soils; however, our modified multi-SIR method is more suitable for organic soils, such as forest floors, that have low bulk density.