δ¹³C and δ¹⁵N are extensively used to understand the biogeochemical mechanisms that moderate ecosystem carbon (C) and nitrogen (N) processes. Little is known about the responses of δ¹³C and δ¹⁵N to alpine grassland degradation on the Qinghai‐Tibetan Plateau (QTP), which prevents a full understanding of degradation‐induced changes in C and N cycling there. We investigated the vegetation δ¹³C and δ¹⁵N, soil δ¹³C and δ¹⁵N, soil properties, and plant community composition of alpine grassland on the QTP that were in different states of degradation. Our results show that the vegetation δ¹³C and δ¹⁵N, and soil δ¹³C and δ¹⁵N, increased with the severity of degradation, whereas soil organic carbon (SOC) and total N content decreased as degradation became more severe. The aboveground biomass percentage of forbs was positively correlated with the soil C/N ratio, vegetation δ¹³C, and soil δ¹³C, and accounted for the largest proportion of the variance for both vegetation δ¹³C and soil δ¹³C (17.25 and 23.65%, respectively). The vegetation δ¹⁵N and soil δ¹⁵N were negatively correlated with the soil C/N ratio, which explained the largest proportion of the variance (18.01 and 25.81%, respectively). Our results suggest that C cycling is strongly moderated by plant community composition, because forbs species and C₄ species, were more prevalent in degraded alpine grassland. Meanwhile, N cycling is indirectly regulated by changes in community composition via its effect on the soil C/N as the degradation became more severe for alpine grassland on the QTP.

中文翻译：

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植物群落的变化决定了退化草地上植被和土壤的δ13C和δ15N富集

δ ¹³ C和δ ¹⁵ N被广泛地用于理解生物地球化学机制，适度生态系统碳（C）和氮（N）工艺。知之甚少的δ的响应¹³ C和δ ¹⁵ N到高山草地退化的青藏高原（QTP），这防止了在C和N循环有劣化引起的变化的充分理解。我们研究了植被δ ¹³ C和δ ¹⁵ N，土壤δ ¹³ C和δ ¹⁵ N，土壤性质，并在QTP高山草原植物群落组成那名降解的不同状态。我们的研究结果表明，植被δ ¹³ C和δ ¹⁵N，和土壤δ ¹³ C和δ ¹⁵ N，与退化的严重程度增加，而土壤有机碳（SOC）和总N含量降低作为降解变得更加严重。杂类的地上生物量百分比呈正与土壤C / N比，植被δ相关¹³ C，和土壤δ ¹³ C，和占方差的两个植被δ最大比例¹³ C和土壤δ ¹³ C（17.25和23.65％）。δ植被¹⁵ N和土壤δ ¹⁵氮与土壤碳氮比呈负相关，这解释了最大的变化比例（分别为18.01和25.81％）。我们的结果表明，C循环受植物群落组成的强烈控制，因为在退化的高山草原上，Forbs和C ₄物种更为普遍。同时，随着QTP上高寒草地退化的加剧，氮素循环通过其对土壤碳氮的影响而间接地受到群落组成变化的调控。