Insect herbivory on seedling leaves is one of the most important factors driving seedling growth and mortality in natural forests, which sets the pivotal roles of insect herbivory in affecting natural forest regeneration and species composition. The intensity of herbivory can be influenced by multiple biotic and abiotic factors affecting leaf detection or consumption by insect herbivores. However, the relative importance of these biotic and abiotic factors in affecting insect herbivory and their interactions remain largely unknown in species-rich forests. We measured insect herbivory on seedling young leaves across 600 1 m × 1 m seedling plots in a subtropical forest. Effects of nine seedling traits, neighboring plant compositions, soil moisture, and light availability on young leaf damage by insect herbivores were assessed with generalized linear mixed-effects models. We found that seedling traits associated with plant size (young leaf area and seedling height), leaf nutrition or defense (leaf thickness, carbon content, and stem specific length) explained more of the variation in insect herbivory than the biotic and abiotic environmental factors. Young leaf coloration (delayed greening degree) exhibited contrasting effects on leaf damage at wet vs. dry sites, so did seedling trait diversity (functional dispersion, FDis). The risk of insect herbivory increased with leaf redness and decreased with seedling FDis at wet sites, while the opposite trends were observed at dry sites. Our study advances the understanding on the driving factors of insect herbivory on seedling leaves in species-rich forests and suggests that the alleviating effects of plant diversity on insect herbivory were stronger at wet conditions.

幼苗叶片上的食草昆虫是驱动天然林中幼苗生长和死亡的最重要因素之一，这决定了昆虫食草植物在影响天然林再生和物种组成中的关键作用。草食的强度会受到多种生物和非生物因素的影响，这些因素会影响叶片检测或昆虫食草动物的食用。但是，在物种丰富的森林中，这些生物和非生物因素在影响昆虫食草及其相互作用方面的相对重要性仍然未知。我们在亚热带森林中的600 1 m×1 m苗地中测量了幼苗幼叶上的食草性。九种苗木性状，邻近植物组成，土壤水分，并利用广义线性混合效应模型评估了昆虫食草动物对幼叶的光利用率。我们发现，与植物大小（幼叶面积和幼苗高度），叶片营养或防御（叶片厚度，碳含量和茎比长）相关的幼苗性状比生物和非生物环境因素更多地解释了昆虫食草的变异。幼叶着色（延迟的绿化度）在潮湿和干燥位置对叶片损伤表现出相反的影响，幼苗性状多样性（功能分散，FDis）也表现出相反的作用。在湿润地区，昆虫食草的风险随叶片变红而增加，而随幼苗FDis降低，而在干燥地区则观察到相反的趋势。