Unlike well-known global patterns of plant species richness along altitudinal gradients, in the mountainous areas of the Brazilian Caatinga, species richness and diversity reach their maxima near mountain tops. The causes of this unusual pattern are not well understood, and in particular the role of edaphic factors on plant community assembly along these gradients has not been investigated. Our goal was to assess the role of edaphic factors (fertility and soil texture) on plant community composition and structure on two mountains of the Brazilian semi-arid region. In 71 plots (Bodocongó site, twenty-one 200-m2 plots, 401–680 m asl; Arara site, fifty 100-m2 plots, 487–660 m asl) we recorded 3114 individuals representing 61 plant species; in addition, at each plot we collected composite soil samples from 0–20 cm depth. Significant altitude-related changes were observed both for community structure and composition, and edaphic variables. A canonical correspondence analysis allowed the distinction of two groups of plots according to species abundances, indicating a preferential habitat distribution of species depending both on altitude and soil variables. Although soil fertility was lowest at the highest altitudes, these areas had high richness and diversity. Conversely, the more fertile foothills were characterized by the dominance of generalist pioneer species. Despite the relatively short altitudinal range that characterizes the studied mountains, this study elucidates the role of edaphic factors on the floristic composition and species richness patterns on the mountains of the Brazilian semi-arid region.

中文翻译：

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土壤因子对巴西半干旱地区沿海拔梯度植物物种丰富度和多样性的作用

与众所周知的沿海拔梯度的植物物种丰富度全球模式不同，在巴西卡廷加的山区，物种丰富度和多样性在山顶附近达到最大值。这种不寻常模式的原因尚不清楚，特别是土壤因素对沿这些梯度的植物群落组装的作用尚未研究。我们的目标是评估土壤因素（肥力和土壤质地）对巴西半干旱地区两座山脉植物群落组成和结构的作用。在 71 个地块中（Bodocongó 遗址，21 个 200 米2地块，401-680 m asl；Arara 站点，50 个 100 米2地块，487-660 m asl）我们记录了代表 61 个植物物种的 3114 个个体；此外，我们在每个地块收集了 0-20 cm 深度的复合土壤样品。群落结构和组成以及土壤变量均观察到与海拔高度相关的显着变化。规范对应分析允许根据物种丰度区分两组地块，表明物种的优先栖息地分布取决于海拔和土壤变量。尽管在最高海拔地区土壤肥力最低，但这些地区的丰富性和多样性很高。相反，更肥沃的山麓以通才先锋物种的优势为特征。尽管所研究山脉的海拔高度范围相对较短，