Interactive effects of temperature and moisture on composition of the soil microbial community

A wealth of knowledge exists on the response of soil processes to variation in environmental factors such as temperature and moisture, but the response from the soil microbial communities that control these processes remains poorly understood. We carried out a full factorial incubation experiment to investigate the single and interactive effects of temperature (10, 17, 24, 31 and 38°C) and moisture (20, 40, 60, 80 and 100% water holding capacity (WHC)) on composition of the soil microbial community characterized by the phospholipid fatty acids (PLFAs) method. The single and interactive effects of temperature and moisture were statistically significant (P < 0.05) for almost all the selected PLFA signatures, including fungi (F), bacteria (B), Gram‐positive bacteria (G⁺), Gram‐negative bacteria (G⁻), actinomycetes (ACT) and the bacterial stress index (BSI). Although the F/B ratio increased and the G⁺/G⁻ ratio decreased with increasing temperature, they were not significantly affected by moisture and its interaction with temperature. In general, the concentrations of fungal PLFAs were smaller at higher temperatures, but not altered by changes in moisture. In contrast, the concentrations of bacterial PLFAs were larger at higher temperatures and moderate moisture contents. Although we manipulated temperature and moisture in the incubation, the treatments and the treatment‐altered soil properties (dissolved organic carbon (DOC) and inorganic nitrogen (ION)) together explained 18% of the total variation in selected PLFA signatures and the temperature effect contributed the most (12%). Significant correlations between community composition variables (F, B and F/B) and soil properties (DOC and ION) indicated substantive indirect effects of temperature and moisture on the composition of the soil microbial community by altering substrate availability. Our results suggest that soil microbial communities might shift towards a more bacteria‐dominated composition under warmer temperatures and moderate moisture conditions in subtropical forest regions. HIGHLIGHTS: How do temperature and moisture independently and interactively affect soil microbial community composition? Concentrations of bacterial PLFAs were larger at higher temperatures and moderate moisture. Concentrations of fungal PLFAs were smaller at higher temperatures, but did not respond to moisture differences. Increased soil carbon and nitrogen availability mainly benefitted bacteria under higher temperatures and moderate moisture.