Environmental filters affect community assembly through the functional traits of species. However, the process of community assembly remains unclear because of the complex interactions among the many biotic and abiotic factors. This study aimed to examine the community assembly process of vascular plants along gradients of elevation (45‒2500 m a.s.l.) and soil nitrogen availability. This study examined the trait distribution patterns of four functional traits (plant height, leaf area, specific leaf area and leaf nitrogen concentration) of vascular plants (trees, herbs and ferns) in central Japan, using null model testing. The number of species decreased and increased at high elevations for tree species and herb and fern species, respectively. The numbers of both tree species and herb and fern species were positively correlated with soil nitrogen availability. Community-weighted means (CWMs) of the four traits decreased with elevation. CWMs and ranges of the three leaf traits were positively correlated with soil nitrogen availability. The community-weighted variance of plant height was higher at higher elevations, indicating that niche differentiation of vertical stratum in habitats with a low canopy was important for community assembly. This study suggests that severe climatic conditions reduce the number of tree species and the canopy height at high elevations, leading to increases in the number of herb and fern species due to increased light intensity at the forest floor. The elevational change of leaf traits also indicates the change of adaptive leaf traits. It further suggests that lower nitrogen availability decreases the number of tree, herb and fern species by excluding those species with leaf traits unsuited to lower nitrogen availability. Therefore, community structure is most likely regulated by both elevation and soil nitrogen availability.

中文翻译：

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沿海拔梯度和土壤氮有效性的植物物种丰富度和群落组装。


环境过滤器通过物种的功能特征影响群落组装。然而，由于许多生物和非生物因素之间复杂的相互作用，群落组装的过程仍不清楚。本研究旨在研究维管束植物沿海拔梯度（45-2500 m asl）和土壤氮素有效性的群落组装过程。本研究采用零模型检验，研究了日本中部维管植物（树木、草本植物和蕨类植物）的四个功能性状（株高、叶面积、比叶面积和叶氮浓度）的性状分布模式。在高海拔地区，树种、草本植物和蕨类植物的物种数量分别减少和增加。树种、草本植物和蕨类植物的数量与土壤氮素有效性呈正相关。四个性状的社区加权平均值（CWM）随着海拔的升高而降低。 CWM 和三个叶片性状的范围与土壤氮素有效性呈正相关。海拔越高，植物高度的群落加权方差越高，表明低冠层生境中垂直层的生态位分化对于群落组装很重要。这项研究表明，恶劣的气候条件会减少高海拔地区的树种数量和树冠高度，由于森林地面光照强度增加，导致草本植物和蕨类植物的数量增加。叶片性状的海拔变化也预示着叶片适应性状的变化。它还表明，较低的氮利用率会排除那些具有不适合较低氮利用率的叶子性状的物种，从而减少树木、草本植物和蕨类植物的数量。 因此，群落结构很可能受到海拔和土壤氮素有效性的调节。