Response of methane emissions to litter input manipulation in a temperate freshwater marsh, Northeast China

Plant litter plays an important role in regulating CH4 emission in wetland ecosystems. Our knowledge of the impacts of plant litter on CH4 budget is important for understanding the response and feedbacks of wetland ecosystems to climate warming. Nevertheless, the effects of plant litter on CH4 emission and temperature sensitivity (Q(10)) are not clear under the background of global change. In this study, a field litter inputs manipulation experiment with four treatments including no aboveground litter (NL), standing litter removal (AR), doubled litter input (DL) and controls (CK) was conducted to study the effects of litter manipulations on CH4 emission in a seasonal inundated freshwater marsh over two growing seasons of 2015 and 2016 in the Sanjiang Plain, Northeast China. Results showed that CH4 emission was significantly associated with altered litter input over the observation period. Compared with CK, the cumulative CH4 emission increased by 105.83%, 42.20% and 42.50% for NL, AR and DL treatments, respectively, in 2015, and the values were 199.04%, 115.55% and 17.55%, in 2016. Variances of CH4 emission were more sensitive to litter removal effects. Altered litter input also significantly affected the dissolved organic carbon (DOC) concentration ([DOC]) in surface pore water. DL and CK treatments with lower soil temperature had lower [DOC] than litter removal treatments of NL and AR. The abundance of methanogens among the four treatments exhibited synchronous change with DOC over the observation period. The Q(10) values of CH4 emission didn't show consistent changing patterns with those of DOC among different litter input treatments, which was probably due to the different temperature sensitivity of dominant methanogen types. Due to its great effects on soil microclimate, substrate availability and the concomitant variation in temperature sensitivity, our results highlighted that plant litter effects should be incorporated into the current process-based CH4 biogeochemical models to predict future CH4 fluxes from natural wetlands under the background of global change.