A research team has found that microbial communities in a large, thermally stratified reservoir changed more strongly from year to year than between surface and deep waters, while their overall metabolic functions remained comparatively stable. The researchers attributed this stability to functional redundancy and the metabolic versatility of 46 keystone microbial taxa capable of participating in carbon, nitrogen, sulfur, and iron transformations. The findings clarify how reservoir microbiomes maintain essential ecosystem processes despite environmental fluctuations and may support future strategies for predicting water-quality changes, controlling eutrophication, and managing large freshwater reservoirs under increasing climatic and human pressures.
Large deep-water reservoirs provide water, generate hydroelectricity, control floods, and support fisheries, but they are also active biogeochemical hotspots. Thermal stratification creates pronounced gradients in temperature, oxygen, light, and nutrients, producing distinct microbial habitats throughout the water column. Previous research has mainly examined seasonal changes and shown that microorganisms regulate carbon turnover, nitrogen retention or removal, sulfur transformations, and iron cycling. However, comparatively little is known about microbial succession across multiple years. In particular, it remains unclear whether year-to-year environmental variation outweighs depth-related differences and how highly connected keystone taxa help preserve ecosystem functions under changing conditions.
A study (DOI: 10.48130/ebp-0026-0006 ) published in Environmental and Biogeochemical Processes on 27 May 2026 by Jun Liu's & Baogang Zhang's team, Huazhong Agricultural University & China University of Geosciences (Beijing), reports that metabolically versatile keystone microorganisms may maintain functional stability even as microbial community composition changes substantially between years.
The researchers investigated the Xiaowan Reservoir on the Lancang River, the upper Mekong River, in southwestern China, from 2017 to 2019. Water was collected at depths of 5 and 80 meters during February and August, with the exception of February 2018. The team measured temperature, pH, dissolved oxygen, oxidation-reduction potential, total organic carbon, chlorophyll a, phosphorus, and several nitrogen- and sulfur-containing compounds. They then combined 16S ribosomal RNA gene amplicon sequencing with shotgun metagenomics to characterize microbial composition and functional potential. Genome binning reconstructed 671 medium- or high-quality metagenome-assembled genomes representing 17 microbial phyla. Statistical analyses were used to compare communities among years and depths, while co-occurrence network analysis identified highly connected microorganisms and linked their distributions to environmental variables. The results showed that interannual variation explained considerably more microbial compositional change than water depth. Community composition differed especially between 2017 and the two subsequent years, and taxonomic dissimilarity increased progressively with time. By contrast, functional dissimilarity increased only modestly, suggesting that different microorganisms could perform overlapping ecological roles and thereby buffer the reservoir's metabolic functions against taxonomic turnover. Functional analysis revealed widespread capacities for organic-carbon degradation, fermentation, carbon monoxide oxidation, carbon fixation, dissimilatory nitrate reduction to ammonium, and urea utilization. The genetic potential for urea use and sulfur oxidation increased annually from 2017 to 2019, indicating adaptive responses to changing nutrient inputs and environmental conditions. Network analysis further identified 46 putative keystone genomes that connected different microbial modules. These taxa carried diverse pathways for carbon utilization, nitrogen transformations, sulfur oxidation, hydrogen metabolism, and iron reduction. Sixteen keystone genomes contained urease genes, while 25 possessed genes associated with sulfur oxidation. No single keystone genome encoded the complete pathway from nitrate to nitrogen gas, suggesting that some transformations may depend on cooperation among microbial groups. Total organic carbon was the strongest measured environmental predictor, explaining 14.3% of the variation in keystone-taxon distribution.
Overall, the study shows that taxonomic change does not necessarily lead to the loss of ecosystem functions in deep-water reservoirs. Instead, functional redundancy and the broad metabolic capabilities of keystone microorganisms may sustain elemental cycling as environmental conditions vary between years. By connecting microbial community dynamics with carbon, nitrogen, sulfur, and iron transformations, the research provides a mechanistic foundation for monitoring reservoir health and anticipating biogeochemical responses to nutrient enrichment, hydrological management, and climate-driven environmental change.
