Abiotic factors and plant traits affect the soil microbial properties in forests across the Japanese archipelago

Understanding the factors that control the structure of soil microbial communities is crucial to predict the responses of terrestrial ecosystems to global change. Microbial biomass, composition, and physiological and nutritional states are known to be influenced by abiotic and biotic factors. However, how they vary and respond collectively to abiotic and biotic factors, particularly in forest ecosystems at the landscape scale, remains unclear. This study applied statistical models to explain variations in soil microbial properties from 18 forest sites covering a wide range of annual temperatures, soil properties, stand ages, and plant leaf traits in the Japanese archipelago. Soil microbial properties were evaluated using phospholipid fatty acid (PLFA) analysis. Our results show that fungal PLFA concentration was mainly explained by soil carbon (C) concentration, whereas bacterial and total PLFA concentrations were predominantly determined by soil nitrogen (N) concentration. The ratio of fungal to bacterial PLFA was best explained by the soil C:N ratio. Most variations in microbial composition and physiological and nutritional states were mainly explained by the mean annual temperature and soil pH. Community-weighted means of plant traits, particularly leaf dry matter content (LDMC), also contributed to explaining the variation in bacterial and total PLFA concentrations as well as physiological and nutritional states indicative of temperature and nutritional stress. These results suggest that abiotic factors and plant traits can shape the microbial community structure in forest soils, and that global warming may affect the soil system by altering the physiological and nutritional states of soil microbes in the Japanese archipelago.