Metabolic coupling of aerobic and anaerobic carbon and nitrogen cycling in plateau riparian zones: asymmetric response in dry and rainy seasons

This study investigates the spatiotemporal characteristics and key driving factors of carbon-nitrogen cycling in riparian wetlands of the Lhasa River Basin on the Qinghai-Tibet Plateau. As the "Third Pole" of the world, the Qinghai-Tibet Plateau is experiencing dual pressures from rapid climate warming and increasing human activities, yet research on carbon-nitrogen cycling processes in high-altitude riparian wetlands remains limited. We collected samples from 58 sites along the upper, middle, and lower reaches of the Lhasa River in August 2020 and May 2021, measuring soil physicochemical properties and potential rates of nitrification, denitrification, anaerobic ammonium oxidation, methane production, and aerobic and anaerobic methane oxidation, along with analyzing the abundance of related functional genes. Results show that riparian zones, as transitional areas between terrestrial and aquatic ecosystems, exhibit distinct redox gradients that support the coupling of various carbon-nitrogen transformation processes. Spatially, these processes are regulated by environmental factors such as organic matter content, oxygen concentration, temperature, and pH, and are closely related to microbial community structure. Seasonal changes influence hydrological conditions and temperature, thereby modulating the intensity of key carbon-nitrogen cycling processes. The study reveals that anaerobic ammonium oxidation may make significant contributions to nitrogen removal in high-altitude riparian zones and forms significant coupling relationships with methane cycling processes, providing new insights into carbon-nitrogen cycling mechanisms in high-altitude regions under climate change. These findings not only reveal the key processes and regulatory mechanisms of carbon-nitrogen cycling in high-altitude riparian zones but also provide a scientific basis for the management and protection of wetland ecosystems in the Lhasa River Basin.