Reply on RC1

Abstract

Alpine peatlands are recognized as a major natural contributor to the budgets of atmospheric methane (CH4) but as a weak nitrous oxide (N2O) source. Anthropogenic activities and climate change have put these fragile nitrogen (N)-limited peatlands under pressure by altering water table (WT) levels and enhancing N deposition. The response of greenhouse gas (GHG) emissions from these peatlands to these twin changes is uncertain. To address this knowledge gap, we conducted a mesocosm experiment in 2018 and 2019 investigating individual and interactive effects of three WT levels (WT-30, 30 cm below soil surface; WT0, soil-water interface; WT10, 10 cm above soil surface) and multiple levels of N deposition (0, 20, 40, 80 and 160 kg N ha-1 yr-1) on growing season CH4 and N2O emissions in the Zoige alpine peatland, Qinghai-Tibetan Plateau. We found that the elevated WT levels increased CH4 emission, while the N deposition had non-linear effects (stimulation at moderate levels and inhibition at higher). In contrast no clear pattern of the effect of WT levels on the cumulative N2O emission was evident, while N deposition led to a consistent and linear increase (emission factor: 2.3 %–2.8 % and 1 % in IPCC), and this was dependent on the WT levels. Across the two years, the scenario with the greatest GWP (from CH4 and N2O) was an N deposition of ca. 20 kg N ha-1 yr-1 and high WT levels (at soil surface or above). Given the current N deposition in the Zoige alpine peatland (1.08–17.81 kg N·ha-1), our results suggested that the CH4 and N2O emissions from the alpine peatlands could greatly increase in response to the possible doubling N deposition in the future. We believe that our results provide insights into how interactions between climate change and human disturbance will alter GHG emissions from this globally important habitat.