Impacts of management and changed hydrology on soil microbial communities in a floodplain forest

Long-term human activities substantially altered floodplain regions of temperate Europe. Forest management and extensive changes in hydrology greatly affected natural floodplain soil properties, in which microbes play key roles. This study aims to assess the effects of human activities through a gradient of forest management intensity on soil microbial community (SMC), its biomass, activity, and structure. Soil chemical and physical-chemical properties were used to explain the general associations and within-site variation using principal component analysis (PCA), linear regression (LR) and linear mixed-effect regression (LMER) models. It was found that forest management application, regardless of its intensity, led to significant microbial biomass reduction. PCA revealed that microbial biomass, expressed as a sum of phospholipid fatty acids along with recalcitrant carbon fraction (ROC) best explained the variability in data. LR and LMER highlighted that bacteria are affected by floodplain forest management more than fungi, and that bacterial response to pH was highly diversified. Also, pH was identified as the best predictor of SMC structure and activity but not of its size. The study calls for further investigation in SMC interactions with ROC, soil-available Fe and Mn, and the role of redox-active metals in soil organic carbon degradation.