Effects of water table level and nitrogen deposition on methane and nitrous oxide emissions in an alpine peatland

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 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, 0 cm at the soil surface; WT10, 10 cm above soil surface) and multiple levels of N deposition (0, 20, 40, 80 and 160 kgNha-1yr-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 emissions, while N deposition had nonlinear effects (with stimulation at moderate levels but inhibition at higher levels). In contrast no clear pattern of the effect of WT levels on the cumulative N2O emissions was evident, while N deposition led to a consistent and linear increase (emission factor: 2.3 %–2.8 %), and this was dependent on the WT levels. 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 CH4 and N2O emissions from this globally important habitat.