Soil microbial necromass carbon (MNC) contributes to the long-term stability of soil organic carbon (SOC). However, the response of MNC across aridity gradients remains unclear, especially in vulnerable alpine ecosystems. Here, we examined alpine grasslands from 180 sites spanning a 3,500 km aridity gradient on the Tibetan Plateau to investigate how MNC abundance and composition (contributions of bacterial and fungal necromass carbon) vary with climate. MNC was variable, ranging from 0.55 to 26.95 g kg⁻¹ soil, with higher content observed in humid and dry-subhumid regions than in arid and semiarid regions in the Western Tibetan Plateau. Soil properties were the dominant drivers of MNC, with soil fertility (cation exchange capacity and total phosphorus) and weathering products (clay, silt and iron/aluminum oxides) facilitating MNC accumulation, while a negative correlation was observed between MNC and soil pH. A pivotal aridity threshold of 0.60 underpinned a non-linear decrease in MNC with increasing aridity across soil condition gradients; MNC was negatively correlated with aridity below this threshold and showed no correlation beyond it. Given this pivotal aridity threshold, we delineated the drivers of MNC under conditions of low (aridity < 0.6) versus high (aridity > 0.6) aridity. In low-aridity conditions, MNC accumulation was governed by aridity, soil fertility, weathering products, and pH, whereas in high-aridity conditions, the interplay between soil properties and temperature took precedence. Species richness enhanced carbon accumulation from microbial residues under low-aridity conditions more so than under high-aridity conditions, with fungal necromass carbon consistently being a higher contributor to SOC than bacterial necromass carbon, particularly in humid regions. These findings highlight aridity-driven divergence in MNC and propose that conserving plant diversity may mitigate the adverse effects of aridification on MNC under low-aridity conditions in alpine grasslands.

土壤微生物坏死物碳（MNC）有助于土壤有机碳（SOC）的长期稳定性。然而，跨国公司对干旱梯度的反应仍不清楚，特别是在脆弱的高山生态系统中。在这里，我们研究了青藏高原 3,500 公里干旱梯度的 180 个地点的高山草原，以研究 MNC 丰度和组成（细菌和真菌坏死物碳的贡献）如何随气候变化。 MNC变化较大，范围为0.55至26.95 g·kg ⁻¹ 土壤，在湿润和半湿润干旱地区观察到的含量高于青藏高原西部干旱和半干旱地区。土壤性质是 MNC 的主要驱动因素，土壤肥力（阳离子交换能力和总磷）和风化产物（粘土、淤泥和铁/铝氧化物）促进 MNC 积累，而 MNC 与土壤 pH 值之间呈负相关。 0.60 的关键干旱度阈值导致 MNC 随着土壤条件梯度的干旱度增加而非线性下降； MNC 与低于该阈值的干旱度呈负相关，超过该阈值则没有相关性。考虑到这一关键的干旱阈值，我们描述了低（干旱度 < 0.6）与高（干旱度 > 0.6）干旱条件下跨国公司的驱动因素。在低干旱条件下，MNC积累受干旱、土壤肥力、风化产物和pH值的影响，而在高干旱条件下，土壤性质和温度之间的相互作用占主导地位。 在低干旱条件下，物种丰富度比在高干旱条件下更能增强微生物残留物的碳积累，真菌死物碳对 SOC 的贡献始终高于细菌死物碳，特别是在潮湿地区。这些发现强调了干旱驱动的跨国公司的分化，并提出保护植物多样性可以减轻高山草原低干旱条件下干旱对跨国公司的不利影响。