Microbial decomposition of soil organic carbon (SOC) is a major determinant of the global climate and terrestrial ecosystem services. Despite the rapid loss of plant species worldwide, it remains unclear how plant species richness impacts SOC decomposition, especially the decomposition of labile vs. recalcitrant SOC. This is partly because of the variable responses of soil C-degrading enzyme activities to plant species richness. Through a global meta-analysis of 490 paired observations of plant mixtures versus monocultures, we show that plant mixtures significantly enhanced soil C-hydrolase (degrades labile C) and C-oxidase (degrades recalcitrant C) activities by 29.4 and 14.9%, respectively. However, in mixtures, C-hydrolase activity marginally (P = 0.051) increased, while C-oxidase activity significantly decreased with plant species richness. In addition, in mixtures, C-hydrolase but not C-oxidase activity significantly increased with plant functional type richness and experimental duration. These plant species richness and functional type effects on C-hydrolase and C-oxidase activities were consistent among diverse terrestrial ecosystems, plant life forms, the presence/absence of legumes, and climate types. Moreover, increases in C-hydrolase but not C-oxidase activity were positively related with increasing microbial biomass C and SOC under plant mixtures, suggesting that faster microbial decomposition and transformation of labile C pools mediate SOC accumulation at higher plant species richness. These results highlight that plant species richness differentially affects labile and recalcitrant C-degrading enzymes, thereby influencing SOC decomposition, dynamics, and accumulation.

土壤有机碳 (SOC) 的微生物分解是全球气候和陆地生态系统服务的主要决定因素。尽管全球植物物种迅速消失，但植物物种丰富度如何影响 SOC 分解，尤其是不稳定 SOC 与顽固 SOC 的分解，仍不清楚。这部分是因为土壤碳降解酶活性对植物物种丰富度的不同反应。通过对 490 对植物混合物与单一栽培的配对观察的全球荟萃分析，我们表明植物混合物显着增强了土壤 C-水解酶（降解不稳定 C）和 C-氧化酶（降解顽固 C）的活性，分别提高了 29.4% 和 14.9%。然而，在混合物中，C-水解酶活性微弱（P = 0.051) 增加，而 C-氧化酶活性随着植物物种丰富度而显着降低。此外，在混合物中，C-水解酶而不是 C-氧化酶活性随着植物功能类型丰富度和实验时间的增加而显着增加。这些植物物种丰富度和功能类型对 C-水解酶和 C-氧化酶活性的影响在不同的陆地生态系统、植物生命形式、豆科植物的存在/不存在和气候类型之间是一致的。此外，C-水解酶而非 C-氧化酶活性的增加与植物混合物下微生物生物量 C 和 SOC 的增加呈正相关，表明微生物分解和不稳定 C 库的转化速度更快，在较高的植物物种丰富度下介导 SOC 积累。