Alpine ecosystem carbon cycling is sensitive to climate change, particularly in 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 μmol 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 (Q₁₀) 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 divergence in both soil nutrient and ecosystem carbon uptake across different vegetation types in an alpine biome transition zone. More similar in situ investigations in various biome transition zones are urgently needed to quantitatively understand the spatial pattern of alpine ecosystem carbon-nitrogen cycling processes.

高山生态系统的碳循环对气候变化敏感，特别是在生物群落之间的过渡带。土壤氮的条件下，其中包括铵硝酸盐（NH ₄ ⁺ / NO ₃ ^- ）的比例，通过偶合碳-氮循环调节生态系统的碳吸收。地球上最大的高山牧场分布在青藏高原，那里的高山生物群落过渡区也广泛分布。然而，它在很大程度上是未知如何土壤NH ₄ ⁺ / NO ₃ ^-比和净生态系统CO ₂在高山生物群落过渡区植被类型之间的交流而变化，由于缺乏的原位实地观察。在这里，我们调查了土壤NH₄ ⁺ / NO ₃ ^-跨高山草原，高山草甸和高山沼泽生态系统比和生态系统的碳通量青藏高原中央生物群落过渡区。结果表明：土壤NH ₄ ⁺ / NO ₃ ^-比为最低的高山草原（最干燥的环境中），其具有最高的土壤pH值和最高的高山沼泽（最潮湿的环境），其具有最低的土壤pH值。我们提出了描述理论框架土壤湿度如何调节土壤NH ₄ ⁺ / NO ₃ ^-通过改变反硝化过程和土壤pH值两者之比。我们进一步发现生长期平均净生态系统CO ₂高山草原，高山草甸和高山沼泽的交换量分别为-1.46，-1.90和-5.43μmolm ^-2 s ^-1。这三个草原之间的净生态系统CO ₂交换差异主要是由生态系统总光合作用的差异而不是生态系统的呼吸作用引起的。高寒草原，高寒草甸和高寒沼泽对生态系统呼吸的温度敏感性（Q ₁₀）分别为1.73±0.05、1.44±0.03和2.43±0.45。我们的研究强调了高山生物群落过渡区中不同植被类型的土壤养分和生态系统碳吸收差异很大。更多类似的原位 迫切需要对各种生物群落过渡区进行调查，以定量地了解高山生态系统碳氮循环过程的空间格局。