Land management, slope positions, and thermal properties as regulators of microbial biomass and community composition

Various land management practices and slope positions can modify the functions and health of soil ecosystems. What is currently unknown is the dependence of microbial biomass and their community composition on in situ measured soil thermal properties. Therefore, this study examined how rotational grazing (Graz), non-grazed forage management (NoGr), and crop rotation (Crop) influences soil thermal properties at 5 different slope positions (summit, shoulderslope, backslope, footslope, and toeslope) and the dependence of total microbial biomass, microbial community composition, and microbial ratios on these variables. It is expected that microbial communities will vary among land management practices and increase downslope, while management practices that increase soil heat capacity will increase microbial biomass. Results showed that total microbial biomass under NoGr management was 22% and 317% greater than Graz and Crop managements, respectively. Similarly, total PLFAs, and the composition and diversity of microbial biomass was greater under NoGr management and at the toeslope position than other management and slope positions, respectively. Additionally, all microbial biomass were negatively related to soil temperature under all management practices. Interestingly, total microbial biomass showed a strong dependence with heat capacity under NoGr management, and a strong dependence with thermal conductivity under Crop management. In general, total microbial biomass and microorganism populations were greater under NoGr management at the toeslope, and this was correlated with greater heat capacity and thermal resistivity.