Interrelationships between bryophytes, pH and phosphate availability in grasslands and on exposed soil in southern Sweden

We aimed to investigate effects of soil pH and phosphate availability on bryophyte species in unshaded dry–mesic habitats, and to explore their implications for bioindication and conservation. Species abundance, pH and water-soluble phosphate data were collected from 1098 relevés in southernmost Sweden. Soil variable effects on 95 bryophyte taxa and species richness were evaluated and visualised as heat maps. Changes in community composition along chemistry gradients were analysed based on cumulative graphs. For 96% of the species, cover differed significantly between plots with low, medium and high pH and phosphate availability; 84% of species were significantly affected by pH, 57% by phosphate, and 54% by pH:PO₄ interaction. Effect sizes were twice as large for pH as for phosphate, and minimal for their interaction. Interaction effects were evident for only a few species, in such cases indicating that low phosphate availability promotes ‘calcifuge’ species at high pH. Community composition changed relatively evenly along all gradients. However, per-plot species richness peaked at around pH 7 at low phosphate availability, and around pH 8 at median phosphate availability, thus reflecting a pH:PO₄ interaction effect. Both pH and phosphate availability strongly affect bryophyte species, and hence community composition and richness, although phosphate is generally less influential. Interaction effects exist but are weak, and low rather than high phosphate availability appears to favour species at suboptimal pH, suggesting that the ‘calcifuge–calcicole’ behaviour of bryophytes may not be determined by toxic aluminium and phosphate solubility, as they are in tracheophytes.

本研究旨在探究土壤pH值与磷酸盐有效性对无遮蔽旱中生生境中苔藓植物（bryophyte）物种的影响，并探讨其在生物指示与物种保护中的应用价值。研究团队从瑞典最南部的1098个植被样方（relevés）中采集了物种多度、土壤pH值以及水溶性磷酸盐数据。针对95个苔藓植物分类群以及物种丰富度，研究人员对土壤变量的影响进行了评估，并以热图（heat map）的形式进行可视化呈现。基于累积曲线图，研究人员分析了植物群落组成沿化学梯度的变化规律。在96%的苔藓植物物种中，不同pH与磷酸盐有效性水平（低、中、高）样方内的物种盖度存在显著差异；其中84%的物种受到pH值的显著影响，57%受磷酸盐有效性的显著影响，另有54%的物种受到pH值与磷酸盐（PO₄）交互作用的显著影响。pH值的效应量约为磷酸盐有效性的两倍，而二者交互作用的效应量则极小。仅少数物种表现出显著的交互作用效应，此类情况表明：在高pH环境下，低磷酸盐有效性会促进嫌钙植物（calcifuge）的生长。植物群落组成沿所有化学梯度的变化均相对均匀。不过，在低磷酸盐有效性条件下，样方内的物种丰富度在pH值约为7时达到峰值；而在中等磷酸盐有效性条件下，峰值则出现在pH值约为8的位置，这一结果反映出pH值与磷酸盐的交互作用效应。尽管磷酸盐有效性的影响通常相对较弱，但pH值与磷酸盐有效性均会对苔藓植物物种产生强烈影响，进而作用于群落组成与物种丰富度。交互作用效应确实存在，但强度较低；且在pH值非最优的环境中，低磷酸盐有效性（而非高磷酸盐有效性）似乎更有利于苔藓植物的生存。这表明，苔藓植物的‘嫌钙-适钙’特性，或许并不像维管植物（tracheophyte）那样由有毒铝离子与磷酸盐溶解度所决定。