4.4 Discerning drivers of abundant and rare community assembly
Revealing the factors affecting the relative influences of deterministic and stochastic ecological processes is important for deeper understanding of community assembly (Tripathi et al., 2018). In this study, we found that forest area had a greater association with the abundant subcommunity assembly than other factors, while TN was more closely correlated with the rare subcommunity assembly (Table 1). The strong associations of βNTI values of abundant and rare subcommunities with differences in forest area and TN, respectively, further suggesting that forest area and TN were the key factors shaping the stochastic and deterministic assembly for abundant and rare subcommunities, respectively (Fig. S5). In recent decades, deforestation is one of the most visible land use changes in the Yarlung Tsangpo River basin (Hao et al., 2021; Harris, 2010). Deforestation, combined with climate-induced soil erosion are the main sources of suspended sediment in the river flow (Shi et al., 2018; Wang et al., 2020a). On the one hand, soil erosion can transfer substantial amounts of nutrients (e.g., TN and NH4-N) into the fluvial sediments to support bacterial growth (Quinton et al., 2010). More importantly, surrounding soil derived bacteria inputs can directly affect bacterial composition and diversity in the fluvial sediments (Crump et al., 2012; Ruiz-González et al., 2015). Thus, our findings reveal the important linkage between land use types and community assembly processes, which might influence the microbial diversity and fluvial sediment ecosystem processes. This is an important issue in need of further research. Future work to explore the precise role of land use types for sediment bacterial community assembly processes, providing scientific support for environmental regulation and ecological security maintenance in the Yarlung Tsangpo River basin is needed.