亚热带-温带过渡区秦岭落叶阔叶林幼苗存活机制

【目的】物种幼苗的存活与各种生物和非生物因素密切相关，研究关键因素对幼苗存活的影响有助于理解群落物种共存的主要作用机制。【方法】以秦岭落叶阔叶林25 hm²固定样地的木本植物幼苗为对象，对11 408棵幼苗的生存动态开展连续5年(2015—2019年)的监测，利用广义线性混合模型(GLMMs)在群落水平上对影响不同年龄阶段幼苗存活的主要生物与非生物因素进行分析。【结果】(1)从群落水平来看，对幼苗存活影响最大的是生物因素，幼苗存活率与同种幼苗邻体密度和同种大树邻体胸高断面积呈显著负相关，与异种幼苗邻体密度呈显著正相关，表明物种在幼苗时期受到强烈的负密度制约效应；(2)从苗龄水平上来看，除了生物因素，影响幼苗存活的主要因素还包括海拔等非生物因素，但非生物因素的影响随着苗龄增大而减小。【结论】影响幼苗存活因素是多样的，其中生物因素的影响更显著，促进秦岭大样地中幼苗共存的主要机制为负密度制约效应。

Study on seedling survival mechanism in a deciduous broad-leaved forest in the subtropical-temperate transition zone in the Qinling Mountains

The survival of species seedlings is closely related to various biotic and abiotic factors. Exploring the effect of key factors on seedling survival can help us to understand species coexistence mechanisms. This study was focused on the woody species seedlings in a 25 hm2 permanent forest dynamics plot in the deciduous broad-leaved forest in the Qinling Mountains, and the generalized linear mixed models (GLMMs) were used to explore the effect of main biotic and abiotic factors on seedling survival. Our results showed that: (1) At the community level, biotic factors played a major role on seedling survival. Seedling survival was significantly negatively correlated with conspecific seedling density and conspecific adult. It also positively correlated with interspecific seedlings density. The results showed that negative density-dependence (NDD) had significant effects on seedling dynamics. (2) At the age class, in addition to biological factors, abiotic factors such as altitude also affected seedling survival. The effect of abiotic factors decreased with the increase of seedling age. In summary, there were various factors affecting seedling survival, among which biological factors were more significant, the main mechanism promoting seedling coexistence was negative density restriction effect in the Qinling Mountains.