CO2 evolution from standing litter of the emergent macrophyte Deyeuxia angustifolia in the Sanjiang Plain, Northeast China

Microbial decay of emergent macrophyte litters in the standing-dead phase is an essential component of litter decomposition and thus carbon (C) cycle in wetland ecosystems. In this study, we examined the amount of microbial respiration from standing litter in a Deyeuxia angustifolia-dominated marsh in the Sanjiang Plain by integrating field studies with laboratory experiments. In the field, CO2 evolution from standing litter exhibited a pronounced diel pattern, with high evolution rates concurring with increasing litter water potential at night. Notably, significant CO2 evolution even existed at temperature of −4 °C. Overall, rates of CO2 evolution showed strong positive correlations with relative humidity and litter water potential. In the laboratory, rates of CO2 evolution from wetted culms and leaves increased with increasing temperature, and the relationship between CO2 evolution rates and temperature could be well described with an exponential model. Based on extrapolation from temperature-adjusted mean CO2 evolution rates and standing litter mass, annual CO2 fluxes of culms (3.07 g C m−2 yr−1) and leaves (6.81 g C m−2 yr−1) accounted for 2.32% (culms, 132.30 g C m−2 yr−1) and 6.94% (leaves, 98.20 g C m−2 yr−1) of the corresponding annual net aboveground production, respectively. In total, microbial mineralization of standing litter only contributed to 1.12% of the ecosystem respiration (880 g C m−2 yr−1). Our results highlight the importance of standing-dead phase in litter decomposition and C cycle in wetlands, and also suggest that CO2 flux from standing litter could even be neglected in assessing C budget in the D. angustifolia-dominated freshwater marshes in the Sanjiang Plain, Northeast China.