Plant species richness (PSR) is known to affect soil organic carbon (SOC) storage. However, due to the complex origin and composition of SOC, mechanisms driving the PSR-SOC relationship are not yet fully revealed, hampering an accurate prediction of SOC dynamics under changing plant diversity. Here we investigate the effect of PSR on SOC accumulation along a natural PSR and stand age gradient in a subtropical forest with plot, litter and soil properties being considered. Biomarkers and soil fractionation are used to delineate plant and microbial components of SOC and their influences on the PSR-SOC relationship in the topsoil (0–10 cm) versus subsoil (30–40 cm). We show that PSR does positively affect SOC concentrations at both depths even after considering the effects of substrate, edaphic properties and stand age. However, the PSR-SOC relationship is driven by different pathways in the topsoil versus subsoil. In the topsoil, PSR exerts a strong additive effect on SOC accumulation after the positive influence of substrate, edaphic properties and stand age, mainly regulated by plant-derived components (represented by lignin phenols, light fraction and particulate organic matter), followed by microbial residues. By contrast, PSR has a positive effect on the accrual of microbial-derived components (represented by amino sugars and mineral-associated organic matter) but not plant residues likely via affecting dissolved organic matter (DOM) and nitrogen availability in the subsoil (i.e., DOM-microbial pathway). As a result, microbial-derived components dominate SOC variations in the subsoil, while plant-derived components play a more important role in the topsoil. These findings provide novel information on the mechanistic links between PSR and SOC accumulation at different depths and highlight the role of PSR on long-term carbon sink potentials of soils, which may aid in predicting soil carbon dynamics with plant diversity changes in Earth's system model.

已知植物物种丰富度 (PSR) 会影响土壤有机碳 (SOC) 储存。然而，由于 SOC 的复杂起源和组成，驱动 PSR-SOC 关系的机制尚未完全揭示，阻碍了对植物多样性变化下 SOC 动态的准确预测。在这里，我们研究了 PSR 对亚热带森林中沿自然 PSR 和林龄梯度的 SOC 积累的影响，并考虑了地块、凋落物和土壤特性。生物标志物和土壤分离用于描绘 SOC 的植物和微生物成分及其对表土（0-10 厘米）与底土（30-40 厘米）中 PSR-SOC 关系的影响。我们表明，即使考虑了底物、土壤特性和林龄的影响，PSR 确实对两个深度的 SOC 浓度产生积极影响。然而，PSR-SOC 关系是由表土和底土中的不同途径驱动的。在表土中，PSR 在底物、土壤特性和林龄的积极影响下对 SOC 积累产生强烈的累加作用，主要受植物源成分（以木质素酚、轻质组分和颗粒有机物为代表）的调控，其次是微生物残留物。相比之下，PSR 对微生物衍生成分（以氨基糖和矿物相关有机质为代表）的产生有积极影响，但对植物残留物的产生有积极影响，这可能通过影响底土中的溶解有机质 (DOM) 和氮可用性（即， DOM-微生物途径）。因此，微生物来源的成分在底土中主导 SOC 变化，而植物来源的成分在表土中发挥更重要的作用。