Soil pH and phosphorus drive species composition and richness in semi-natural heathlands and grasslands unaffected by twentieth-century agricultural intensification

<b><i>Background</i></b>: Increased soil phosphorus (P) caused by agricultural intensification has been associated with decreased plant species richness (SR) in central Europe. How plant communities and soil P gradients are related in unimproved open habitats remains unclear. <b><i>Aims</i></b>: The aim of this article was to characterise the relationship between soil chemical parameters and plant species composition and richness in unimproved open habitats. <b><i>Methods</i></b>: The influence of soil chemical parameters (pH, P, K, Mg) on species composition was assessed, using data from 40 heathland and 54 grassland plots, by non-metric multidimensional scaling and permutational multivariate analysis of variance. The relationship between soil chemical parameters and SR was tested by linear mixed effects models. <b><i>Results</i></b>: A direct relationship between heathland community composition and pH was observed, explaining 10% of variation in species composition, while P, Mg and pH together explained 17% of variation in grassland composition. In heathlands, SR increased with increasing pH, whereas in grasslands, SR decreased with increasing soil P. <b><i>Conclusions</i></b>: Soil chemical parameters were substantially related to plant community composition and richness. In an area spared from a century of agricultural intensification, reduced pH appeared to constrain SR in heathlands, while even slight P increases (&lt;10 mg kg⁻¹) depressed plant SR in semi-natural grasslands.

**背景**：中欧地区农业集约化导致的土壤磷（P）富集，已被证实与植物物种丰富度（SR）下降存在关联。但在未改良的开放生境中，植物群落与土壤磷梯度之间的具体关联仍不明确。
**目的**：本研究旨在解析未改良开放生境中，土壤化学参数与植物物种组成及丰富度之间的关联关系。
**方法**：本研究依托40个石楠灌丛样地与54个草地样地的调查数据，采用非度量多维标度法（non-metric multidimensional scaling）与置换多元方差分析（permutational multivariate analysis of variance），评估了土壤化学参数（pH、P、K、Mg）对物种组成的影响；同时通过线性混合效应模型（linear mixed effects models），检验了土壤化学参数与植物物种丰富度之间的关联。
**结果**：研究发现石楠灌丛群落组成与pH值存在直接关联，该关联可解释物种组成10%的变异；而土壤磷、镁与pH值三者共同解释了草地群落组成17%的变异。在石楠灌丛中，植物物种丰富度随pH值升高而增加；但在草地样地中，植物物种丰富度则随土壤磷含量上升而下降。
**结论**：土壤化学参数与植物群落组成及丰富度存在显著关联。在未经历百年农业集约化的区域，pH值降低会抑制石楠灌丛的植物物种丰富度；而在半自然草地中，即便土壤磷含量仅小幅提升（<10 mg kg⁻¹），也会对植物物种丰富度产生抑制作用。