Effects of Heavy Degradation on Alpine Meadows: Soil N2O Emission Rates and Meta-Analysis in the Tibetan Plateau

Heavy grassland degradation is evident across the Tibetan Plateau. However, atmospheric nitrous oxide (N2O) emission rates and their underlying driving mechanisms in the southeast regions and across the Tibetan Plateau remain unclear. We analyzed the N2O emission rates of heavily degraded and undegraded alpine meadow soil incubation using gas chromatography in three river sources and meta-analysis methods across the Tibetan Plateau. The N2O emission rates of the heavily degraded and control meadows were respectively 4.29 +/- 0.64 and 3.27 +/- 0.53 g kg(-1) h(-1) in the southeast Tibetan Plateau (p < 0.01), indicating an increase of 31.16% on the N2O flux of heavy degradation. Heavy degradation increased N2O emission rates by 0.55 +/- 0.14 (95% confidence interval: 0.27-0.83) through meta-analysis. High degradation increased by approximately 71.6% compared with that of the control. The water-filled pore space (WFPS) significantly influenced the N2O emission rate based on the moderator test (p < 0.05). The mixed-effect model results revealed that WFPS, soil nitrate, and bulk soil could explain 59.90%, 16.56%, and 15.19% of the variation in the N2O emission rates between the control and heavily degraded meadows, respectively. In addition, the N2O emission rates of heavily degraded meadows can be reduced by increasing WFPS and bulk density, and by reducing the soil nitrate content.