Aims Over the past 20 years, alpine wetlands have been subjected to a rapid change in climate, resulting in water table drawdown and increased nitrogen deposition. In wetland ecosystems, the water table drawdown can improve soil aeration, hence leading to a higher soil respiration rate; whereas an increased nitrogen deposition could reduce the microbial biomass and pH value, suppressing soil respiration. Understanding the responses of soil respiration to reduced water table and increased nitrogen deposition in alpine wetlands is thus critical to predicting the carbon cycle of wetland ecosystems and its feedbacks to ongoing climate changes. This study tests the effects of water table reduction and nitrogen addition on soil respiration in the Luanhaizi wetland on the Qinghai-Xizang Plateau.
Methods We imposed four treatments, including control (WT⁰N⁰), reduced water table (WT^-N⁰), nitrogen addition (WT⁰N⁺), and a combination of reduced water table and nitrogen addition (WT^-N⁺), on 20 peat monoliths collected from the Luanhaizi wetland at the Haibei station. Soil respiration was measured from late July through mid-September under all treatments.
Important findings A reduction in water table significantly increased the rate of soil respiration. In contrast, nitrogen addition suppressed soil respiration only when water table was not reduced. A positive correlation was found between the aboveground biomass and soil respiration, while no correlation was detected between root biomass and soil respiration. The temperature sensitivity of soil respiration was increased by reduced water table, but was not affected by nitrogen addition. Our results suggest that nitrogen deposition is likely to reduce soil CO₂ emission in alpine wetlands where water level remains high. However, future warmer and drier conditions could result in reduced water table, and consequently alpine wetlands would be predicted to release substantially more CO₂ than previously estimated.