Longitudinal variation of microbial communities in benthic biofilms and association with hydrological and physicochemical conditions in glacier-fed streams

Glacier-fed streams are highly dynamic environments that integrate upstream catchment processes and are prominent geomorphological and ecological components of alpine landscapes. In these systems, hydrological and physicochemical factors change significantly with location downstream of the glacier. Variation in microbial communities in benthic biofilms along such gradients are not well studied, nor do we understand how hydrological and physicochemical factors drive those changes. We characterized microbial community structure in 2 glacier-fed streams in the Tianshan Mountains, central Asia, by sequencing 16S ribosomal (r)RNA genes in benthic biofilms and documented abiotic environmental conditions. Alpha diversity indices of microbes in benthic biofilms (number of operational taxonomic units, evenness, phylogenetic diversity) were significantly related to hydrological factors, including distance to glacier (GD), glacier area proportion (GA), and glacier source proportion (GS), and physicochemical factors, including water temperature, pH, dissolved organic C (DOC), total N (TN), and NO3. The dominant phyla were Proteobacteria (46% of operational taxonomic units [OTUs]), Cyanobacteria (16%), Bacteroidetes (12%), Actinobacteria (9%), and Acidobacteria (6%). Microbial communities differed longitudinally along the stream at the OTU level and even at the phylum level. Correlation, canonical correlation, and network analyses showed that the microbes had significant associations with hydrological (GA, GS, and GD), biogeochemical (TN, NO3, DOC, total P, and soluble reactive P), and physicochemical (pH) factors. These results add to our knowledge of microbial community structure and potential drivers of that structure in glacier-fed stream ecosystems and provide potentially valuable data for assessing future dynamics as these systems experience further disruption caused by the influences of climate change.