Litter affects CO2 emission from alpine wetland soils experiencing drying-rewetting cycles with different intensities and frequencies

The frequency and intensity of drying-rewetting cycles can influence soil CO2 emission from the soil and carbon (C) and nitrogen (N) in the soil, but little is known about whether such effects can be altered by litter input into the soil, especially for alpine wetland ecosystems. We conducted a 144-day incubation experiment at 15 degrees C using the soil and litter collected from an alpine wetland on the Qinghai-Tibetan Plateau, China. The soil added with 1 g litter or not was subjected to two frequencies (high vs. low, i.e. 18 vs. 9 cycles with 8 vs. 16 days per cycle, corresponding to 100% vs. 50% of the precipitation frequency in that wetland) and two intensities (high vs. low, i.e. 360 mm vs. 252 mm, corresponding to 100% vs. 70% of precipitation in that wetland) of drying-rewetting cycles. Soil moisture was higher in the high than in the low intensity treatment; litter addition affected soil moisture, but such an effect depended on the time of incubation. Low frequency and high intensity of drying-rewetting cycles significantly enhanced CO2 emission due to increases in available substrate, e.g., soil dissolved organic C, which might result in increased activity of soil microbes such as Acidobacteria, Proteobacteria, Actinobacteria, Basidiomycota and Ascomycota. Adding litter to the soil increased CO2 emission from the soil likely due to increased water holding capability and labile C availability. In the low intensity and high frequency treatment concentrations of inorganic N, ammonium N and nitrate N were higher in the soil with than without litter addition, but in the high intensity treatment of both low and high frequency concentrations of inorganic N and nitrate N were lower. CO2 emission was positively correlated with the concentration of dissolved organic C and soil moisture, but negatively correlated with the concentration of ammonium N. Our results suggest that low frequency of drying-rewetting cycles combined with litter addition can enhance soil CO2 emission, and that effects of drying-rewetting cycles should be taken into account when we consider greenhouse gas emission from alpine wetland soils.