Divergence in ecosystem carbon fluxes and soil nitrogen characteristics across alpine steppe, alpine meadow and alpine swamp ecosystems in a biome transition zone

• Published in: Science of The Total Environment
• Main Authors: Liu, Yongwen, Geng, Xiaodong, Tenzintarchen, Wei, Da, Dai, Dongxue, Xu-Ri
• Format: Report
• Language: English
• Published: ELSEVIER 2020
• Subjects: Climate change; Carbon and nitrogen cycling; Net ecosystem carbon dioxide exchange; Gross ecosystem photosynthesis; Denitrification rate; Tibetan Plateau; BIOLOGICAL NITRIFICATION INHIBITION; CLIMATE-CHANGE; OXIDE EMISSIONS; VEGETATION CHARACTERISTICS; TEMPERATURE SENSITIVITY; INORGANIC NITROGEN; CO2 EXCHANGE; ICE CORE; MOISTURE; Environmental Sciences & Ecology; Environmental Sciences; ice core
• Online Access: http://ir.imde.ac.cn/handle/131551/50663; https://doi.org/10.1016/j.scitotenv.2020.142453

Alpine ecosystem carbon cycling is sensitive to climate change, particularly in the transition zones between biomes. Soil nitrogen conditions, including the ammonium to nitrate (NH4+/NO3-) ratio, regulate ecosystem carbon uptake by coupling carbon-nitrogen cycle. The largest alpine pasture on Earth is distributed on the Tibetan Plateau, where alpine biome transition zones are also widely distributed. However, it is largely unknown how the soil NH4+/NO3- ratio and net ecosystem CO2 exchange vary among vegetation types in the alpine biome transition zones due to a lack of in situ field observations. Here, we investigated soil NH4+/NO3- ratio and ecosystem carbon fluxes across alpine steppe, alpine meadow and alpine swamp ecosystems in a biome transition zone on the central Tibetan Plateau. The results showed that soil NH4+/NO3- ratio was lowest in the alpine steppe (driest environment), which had the highest soil pH, and highest in the alpine swamp (wettest environment), which had the lowest soil pH. We proposed a theoretical framework describing how soil moisture regulates soil NH4+/NO3- ratio by altering both the denitrification process and soil pH. We further found that the growing season average net ecosystem CO2 exchange for the alpine steppe, alpine meadow and alpine swamp was -1.46, - 1.90 and -5.43 mu mol m(-2) s(-1), respectively. This divergence in net ecosystem CO2 exchange across the three grasslands is primarily explained by divergence in gross ecosystem photosynthesis, rather than ecosystem respiration. The air temperature sensitivity of ecosystem respiration (Q(10)) for the alpine steppe, alpine meadow and alpine swamp was 1.73 +/- 0.05, 1.44 +/- 0.03 and 2.43 +/- 0.45, respectively. Our study highlights large differences in both soil nutrient and ecosystem carbon uptake across different vegetation types in an alpine biome transition zone. More in situ investigations in various biome transition zones are urgently needed to quantitatively understand the spatial pattern of alpine ecosystem ...