Cross-altitude distribution patterns of bacterial communities in Chinese rivers: evidence from meta-analysis

Altitudinal gradients shape river ecosystems through topographical and climatic heterogeneity, yet our understanding of bacterial community responses across altitude remains limited. We analyzed bacterial community structure in Chinese river systems using 2657 high-throughput sequencing samples from 175 publications (2008-2024) to reveal altitudinal distribution patterns and driving mechanisms of in water and sediments. Analysis revealed distinct bacterial compositions: river water was dominated by Proteobacteria (46.3 %), Actinobacteriota (17.0 %), and Bacteroidota (14.0 %); while sediments were characterized by Proteobacteria (43.6 %), Bacteroidota (9.9 %), and Chloroflexi (8.4 %). Both habitats showed significant altitudinal diversity patterns, with water communities exhibiting a hump-shaped diversity pattern and sediments showing a more complex double-humped pattern. Altitude shaped bacterial communities directly via climate variables in water, predominantly indirectly through human activities (indicated by Nighttime Lights, NTL) and physicochemical factors in sediments. Along altitudinal gradients, bacterial communities transition from anthropogenic and nutrient-driven controls at low-altitude gradient terrain to climate and phosphorus-limited regimes at high-altitude gradient terrain. These results demonstrate microbial vulnerability to environmental change and highlight the importance of integrated river management strategies that consider both climate change and human impacts.