Microbial Diversity and Biogeochemical Cycling of Nitrogen and Sulfur in the Source Region of the Lancang River on the Tibetan Plateau

The Tibetan Plateau is known as the "third pole" on Earth, influencing regional and global climates and providing fresh water to billions of people. Climate change and anthropogenic activities are increasingly threatening vulnerable ecosystems therein, but impacts on biogeochemical cycling and the microbial community are largely unknown. Hence, we characterized the distribution of nitrogen and sulfur species and bacterial communities from river water, sediment, and surrounding soils in the hard-to-access source region of the Lancang River. The dominant bacterial genera across Lancang River water were quite consistent, whereas they varied largely in different surface soils. Temperature was found to be a vital driver of bacterial community distribution in river water, while NH4+-N and reduced inorganic sulfur were inferred as major environmental drivers in soils. Unclassified Nitrosomonadaceae and Nitrospira were prevalent in all habitats. Network analysis inferred Nitrospira as a potential keystone genus. nirS genes and nitrite reductase quantification reveal denitrification proceeded in a 100-120 cm soil layer. The abundance of adenosine phosphosulfate reductase increased from the 30 cm soil layer upward, indicating more active sulfate reduction. Overall, this study provides the first comprehensive characterizations of biogeochemical cycling of nitrogen and sulfur from different habitats in the source region of the Lancang River.