Responses of ecosystem respiration and methane fluxes to warming and nitrogen addition in a subtropical littoral wetland

Subtropical wetlands sequester vast carbon (C) and their C cycles are sensitive to global changes, such as climate warming and increased nitrogen (N) deposition. However, little is known about the effects of warming and increased N deposition on ecosystem respiration (Re) and methane (CH4) emission from subtropical wetland ecosystems. In this study, a manipulated warming and N addition experiment was conducted at a subtropical wetland in the littoral zone of Poyang Lake, China. Both Re and CH4 fluxes presented clear seasonal variations under all treatments. Warming significantly decreased Re by 20% compared with no warming and warming effect varied with growing season. Nevertheless, effects of N addition and the interaction of two treatments on Re were not detectable throughout the experimental period. Regardless of growing seasons, no treatments affected the temperature sensitivity of Re compared with the control. Contrary to the Re, CH4 flux was not affected by warming, but significantly affected by N addition and its interaction with warming in the whole and spring growing seasons. N addition decreased CH4 emission by 60% and 52% in the whole and spring growing seasons regardless of warming. Soil temperature was the primary driver for Re and explained about 60% of Re variation, while its explanation on CH4 flux was 13%. Soil moisture was not a limiting factor for Re and CH4 flux in this region. Our results imply that effects of warming and N addition on Re and CH4 flux varied with seasons, and these global changes tend to suppress carbon dioxide (CO2) and CH4 emission from this subtropical littoral wetland based on a short-term experiment. However, longer-term experiments are needed to see if this trend would persist and these effects should be included to project how the C sink function of subtropical littoral wetlands would respond to global changes.