A quantitative understanding of temporal patterns of soil respiration (SR) and its components, as well as of their controlling factors, are key to the estimation of grassland C sequestration under different scenarios of land-use change and global change. However, the sensitivity of seasonal patterns and magnitude of SR and its components to N addition (N) and grazing (G) and their interactions remains poorly understood. We carried out an experiment with N, G and N addition plus grazing (NG) treatments in temperate meadow steppe located in the easternmost of the Eurasian steppe. We measured SR and its components, i.e., autotrophic respiration (AR) and heterotrophic respiration (HR), along with a suite of other biotic and abiotic factors over 3 years. N addition increased AR when compared to the control treatment (CK), whereas moderate grazing decreased AR, and N addition and grazing had additive effects on AR. We found that aboveground biomass was the predominant controlling factor of AR. However, the N, G and NG treatments had no significant effects on HR. Although N addition and grazing caused changes in a series of biotic and abiotic factors (e.g. total PLFAs, soil fungal/bacterial ratio and bulk density) that controlled soil microbial metabolic processes, collectively these effects on HR appeared to offset each other. Moreover, compared to the CK and N treatments, G and NG treatments reduced the apparent temperature sensitivity (Q₁₀) of AR and HR. Grazing dampened the positive response of Q₁₀ of HR to N addition. Our study suggests that AR and HR are regulated by different underlying mechanisms and respond differently to N and G, and therefore should be modeled separately to improve models and predictions of ecosystem C cycling. Our study also indicates that moderate grazing could produce beneficial effects on meadow steppe carbon sequestration under future scenarios of nitrogen deposition and climate warming.

定量了解土壤呼吸 (SR) 及其组成部分及其控制因素的时间模式，是估算不同土地利用变化和全球变化情景下草地固碳的关键。然而，季节性模式和 SR 的大小及其成分对 N 添加 (N) 和放牧 (G) 及其相互作用的敏感性仍然知之甚少。我们在位于欧亚草原最东端的温带草甸草原进行了 N、G 和 N 添加加放牧 (NG) 处理的实验。我们在 3 年内测量了 SR 及其组成部分，即自养呼吸 (AR) 和异养呼吸 (HR)，以及一系列其他生物和非生物因素。与对照处理 (CK) 相比，N 添加增加了 AR，而适度放牧降低了AR，而N添加和放牧对AR有累加效应。我们发现地上生物量是AR的主要控制因素。然而，N、G 和 NG 处理对 HR 没有显着影响。尽管氮的添加和放牧导致控制土壤微生物代谢过程的一系列生物和非生物因素（例如总 PLFA、土壤真菌/细菌比和容重）发生变化，但这些对 HR 的影响似乎相互抵消。此外，与 CK 和 N 处理相比，G 和 NG 处理降低了表观温度敏感性（尽管氮的添加和放牧导致控制土壤微生物代谢过程的一系列生物和非生物因素（例如总 PLFA、土壤真菌/细菌比和容重）发生变化，但这些对 HR 的影响似乎相互抵消。此外，与 CK 和 N 处理相比，G 和 NG 处理降低了表观温度敏感性（尽管氮的添加和放牧导致控制土壤微生物代谢过程的一系列生物和非生物因素（例如总 PLFA、土壤真菌/细菌比和容重）发生变化，但这些对 HR 的影响似乎相互抵消。此外，与 CK 和 N 处理相比，G 和 NG 处理降低了表观温度敏感性（Q ₁₀ ) 的 AR 和 HR。放牧抑制了 HR 的Q ₁₀对 N 添加的积极响应。我们的研究表明，AR 和 HR 受不同的潜在机制调节，对 N 和 G 的反应不同，因此应分别建模以改进生态系统 C 循环的模型和预测。我们的研究还表明，在未来的氮沉降和气候变暖情景下，适度放牧可以对草甸草原碳封存产生有益影响。