Belowground bacterial communities and carbon components contribute to soil respiration in a subtropical forest

Purpose Forest ecosystems are crucial for maintaining high levels of bacterial diversity and containing high amounts of carbon (C), both of which play essential roles in regulating C cycling in the soil and atmosphere through the processes of soil respiration and plant photosynthesis. However, how bacterial communities and different soil carbon components (e.g., soil organic carbon (SOC), readily oxidizable organic carbon (ROC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC)) impact the soil respiration remains largely unknown. Therefore, we hypothesize that belowground bacterial communities and soil carbon contribute to soil respiration, which further influences soil carbon storage.Methods We collected 24 soil samples from Mount Lu (subtropical forest ecosystem, China) along an elevation gradient consisting in eight levels. Here, we used high-throughput sequencing to detect bacterial alpha and beta diversity. We also measured several soil carbon variables, including SOC, ROC, DOC, and MBC. Particularly, regression analysis, structural equation modeling and random forest analysis were applied to explore the effects of bacterial diversity and soil carbon on soil respiration using R-3.6.2.Results The results showed that soil respiration has a clearly positive linear regression (R2 = 0.35-0.61, p < 0.01) with all measured soil carbon components, including SOC, ROC, DOC, and MBC. Bacterial communities composition was significantly divergent along the elevation levels, primarily due to species replacement. Random forest and structural equation modeling analysis confirmed that soil carbon and bacterial beta diversity were the significant driving forces behind soil respiration. Additionally, bacterial communities composition significantly impacted changes in soil respiration, with five identified rare bacterial phyla (WPS-2, Gemmatimonadetes, Verrucomicrobia, Planctomycetes, and Cyanobacteria) significantly correlated with soil respiration. Meanwhile, random forest regression analysis showed that rare bacterial taxa, rather than abundant ones, were the primary bacterial predictors of soil respiration.Conclusion Taken together, belowground bacterial communities and soil carbon variables jointly contribute to soil respiration in a subtropical forest, and further regulate soil C storage as well as even influence climate change.