Abstract: Litter, an important carrier of plant-soil feedback, plays a crucial role in regulating vegetation dynamics and composition in understory. In this study, we measured canopy density, litter biomass, total nitrogen content (TN), and total phosphorus content (TP), along with surveys of understory vegetation across three forest types (coniferous, mixed, and broad-leaved forests) on the southeastern Yunnan-Guizhou Plateau. The structural equation model was used to explore the effects of litter characteristics on species diversity in understory across different forest types. The results showed that: (1) Litter biomass differed significantly among forest types, with coniferous forests (10.19±1.41 t·hm^-2) > mixed forests (7.68±1.22 t·hm^-2) > broad-leaved forests (5.99±0.91 t·hm^-2) (P<0.05). TN contents in litter were significantly higher in broad-leaved and mixed forests than those in coniferous forests (P<0.05), while TP contents in litter were significantly higher in broadleaved forests than in both mixed and coniferous forests (P<0.05). (2) Understory species diversity increased significantly with increasing litter biomass, TN content, and TP content across different forest types (P<0.05). (3) Structural equation model indicated that forest type directly influenced understory species diversity and also exerted indirect effects through canopy density, litter biomass, TN and TP contents. Both forest type and canopy density had direct effects on litter biomass. Furthermore, litter biomass, TN, and TP contents exhibited significant positive direct effects on understory species diversity. Therefore, forest structure optimization and litter management are critical for biodiversity conservation and sustainability in the fragile forest ecosystems of the Yunnan-Guizhou Plateau.

Key words: litter biomass, nutrient content, understory species diversity, structural equation model