Microbial communities in large reservoirs may change markedly from year to year, yet the essential processes they perform can remain surprisingly stable. A new study of the Xiaowan Reservoir in southwest China shows that a small group of highly connected microorganisms may help maintain carbon, nitrogen, sulfur, and iron cycling despite major shifts in the wider microbial community.
"Our findings suggest that ecosystem stability does not necessarily depend on keeping the same microbial species year after year," said co-corresponding author Baogang Zhang. "Instead, metabolically versatile keystone microorganisms may help sustain critical functions as environmental conditions change."
Large deep-water reservoirs provide drinking water, hydropower, flood control, and fisheries, but they also create complex aquatic environments. Seasonal thermal stratification separates warm, oxygen-rich surface water from deeper layers with lower oxygen availability. Nutrient inputs from surrounding agriculture, aquaculture, forests, and human activity can further influence water quality and microbial metabolism.
To understand how reservoir microbiomes respond over longer periods, researchers examined water collected from the Xiaowan Reservoir between 2017 and 2019. Samples were obtained from depths of 5 and 80 meters during winter and summer sampling periods.
The team combined 16S ribosomal RNA gene sequencing with genome-resolved metagenomics. This approach allowed the researchers to identify changes in microbial community composition and reconstruct the metabolic capabilities of individual microbial populations.
The results showed that differences between years were stronger than differences between water depths. Microbial communities sampled in 2017 were compositionally distinct from those collected in 2018 and 2019, and taxonomic dissimilarity continued to increase over time.
However, microbial functions changed less dramatically than microbial identities. This pattern points to functional redundancy, meaning that different microorganisms can perform similar ecological roles. As some populations declined and others increased, the reservoir microbiome retained much of its overall capacity for biogeochemical cycling.
The researchers reconstructed 671 metagenome-assembled genomes spanning 17 microbial phyla. Network analysis identified 46 putative keystone microbial taxa that acted as connectors between different parts of the microbial community.
These keystone microorganisms carried genes associated with diverse processes, including organic carbon utilization, fermentation, nitrate reduction, urea hydrolysis, sulfur oxidation, oxygen respiration, and iron reduction. Their broad metabolic potential may allow them to remain active under changing nutrient and oxygen conditions.
The study also found that the potential for urea utilization and sulfur oxidation increased from 2017 to 2019. Urea can enter reservoirs through fertilizers, phytoplankton decomposition, and microbial activity, while sulfur compounds may be influenced by runoff and organic matter transformation. These trends suggest that microbial communities were adjusting to changing nutrient sources.
Among the measured environmental factors, total organic carbon was the strongest predictor of keystone microbial distribution, explaining 14.3 percent of the variation. Organic carbon can support microbial respiration and mineralization while helping create low-oxygen microenvironments, particularly in deeper water during stratified periods.
"Our study highlights the importance of looking beyond which microorganisms are present," said co-corresponding author Jun Liu. "Understanding what key microbial groups are capable of doing can provide a clearer picture of how reservoirs respond to long-term environmental variability."
The findings may support improved monitoring and management of large reservoirs by identifying microbial functions and environmental indicators linked to nutrient cycling, eutrophication risk, and ecosystem resilience.
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Journal reference: Shi J, Hu W, Huang S, Liu J, Zhang B. 2026. Keystone microbial taxa with interannual dynamics and metabolic versatility drive element biogeochemical cycling in a large deep-water reservoir. Environmental and Biogeochemical Processes 2: e011 doi: 10.48130/ebp-0026-0006
https://www.maxapress.com/article/doi/10.48130/ebp-0026-0006
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About the Journal:
Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
