Altitudinal patterns of bacterial communities in river water and sediments: A meta-analysis across Chinese river systems

Despite the fundamental role of altitudinal gradients in shaping river ecosystems through complex topographical and climatic heterogeneity, our understanding of bacterial community responses along altitude remains limited. Here, we analyzed bacterial community structure in Chinese river systems by compiling a comprehensive dataset of 2,664 high-throughput sequencing samples from 172 publications (2008-2023) and aimed to uncover the altitudinal distribution patterns and driving mechanisms of bacterial communities in river water and sediments. Analysis revealed distinct bacterial compositions between water (dominated by Proteobacteria 46.3%, Actinobacteriota 17.0%, and Bacteroidota 14.0%) and sediment habitats (characterized by Proteobacteria 43.6%, Bacteroidota 9.9%, and Chloroflexi 8.4%). Both habitats exhibited significant altitudinal patterns in diversity and dominant phyla composition. Water bacterial communities exhibited a classic hump-shaped diversity pattern with increasing altitude, explained by the mid-domain effect and scale-dependent diversity mechanisms. In contrast, sediment bacterial communities showed a more complex double-humped pattern, attributed to habitat-specific characteristics and environmental heterogeneity. Altitude shaped bacterial communities through different mechanisms: directly and through climate variables in water, while primarily through human activities (indicated by NTL) and local environmental factors in sediment. Along the altitudinal gradient, the primary factors governing bacterial communities transition from anthropogenic pressures (indicated by NTL) and nutrient pollution in low-altitude gradient terrain to climate and phosphorus limitation in high-altitude gradient terrain. These results highlight the vulnerability of river bacterial communities to environmental changes and underscore the importance of integrated river management strategies that consider both climate change and human impacts.