Carbon management practices regulate soil bacterial communities in response to nitrogen addition in a pine forest

Abstract

Carbon (C) and nitrogen (N) represent the commonest limiting nutrients for microbial growth in terrestrial ecosystems. However, most of our understanding of how C:N ratios modulate microbial growth comes from short-term growth assays under controlled conditions. Four levels of N additions including control (CK, 0 kg·hm− 2·a− 1), low N (LN, 50 kg·hm− 2·a− 1), medium N (MN, 100 kg·hm− 2·a− 1), and high N (HN, 150 kg·hm− 2·a− 1) inputs were applied monthly in a pine forest (Pinus tabulaeformis). Three C management practices were further conducted in each N additions plot, namely aboveground litter and belowground root removal (LRR), aboveground litter removal (LR), and intact soils (non-removal, NR). Soil bacterial richness, diversity, community composition and soil properties were measured. MN and HN significantly increased the relative abundance of copiotrophic taxa, but decreased that of oligotrophic taxa. Bacterial richness and diversity were not altered by N enrichment. LRR significantly increased the relative abundance of Gemmatimonadetes while decreased that of Actinobacteria. C management did not affect bacterial richness and community structure but LR significantly decreased bacterial diversity. Structural equation modeling showed that N addition induced the decrease in soil pH was responsible for the changes in the bacterial community structure. C management exhibited a direct negative effect on bacterial diversity and had an indirect positive effect on it via increasing soil moisture and microbial biomass C:N ratio. The findings highlight the contrasting impacts of N addition and C management on soil bacterial communities and emphasize the regulation of above- and below-ground C substrate supplies on the N responses of soil bacterial communities.