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值与有效磷含量对无遮蔽旱中生境中苔藓植物（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。研究人员从瑞典最南部的1098个植被样方（relevé）中采集了物种多度、土壤pH值与水溶性有效磷数据。针对95个苔藓植物类群与物种丰富度，研究人员对土壤变量的影响进行了评估，并以热图（heat map）形式可视化呈现。基于累积曲线图，研究人员分析了群落组成沿化学梯度的变化规律。在96%的苔藓植物物种中，不同低、中、高pH值与有效磷含量水平样方内的物种盖度存在显著差异；其中84%的物种受pH值显著影响，57%受有效磷含量影响，54%受pH值与磷酸盐（PO4）交互作用的影响。pH值的效应量约为有效磷的两倍，而二者交互作用的效应量则极小。仅少数物种呈现出显著的交互作用效应，此类情形表明：在高pH值环境下，低有效磷含量会促进避钙植物（calcifuge）的生长。群落组成沿所有化学梯度的变化相对均匀。但在低有效磷含量条件下，单样方物种丰富度在pH值约为7时达到峰值；而在中等有效磷含量条件下，峰值则出现在pH值约为8时，这一结果反映了pH值与磷酸盐的交互作用效应。尽管有效磷的影响通常相对较弱，但土壤pH值与有效磷含量均会对苔藓植物物种，进而对群落组成与物种丰富度产生强烈影响。交互作用效应确实存在但强度较弱；相较于高有效磷含量，低有效磷含量似乎更有利于处于非最适pH值环境中的物种生存。这表明苔藓植物的避钙（calcifuge）与适钙（calcicole）特性，可能并不像维管植物（tracheophyte）那样由有毒铝离子与磷酸盐溶解度所决定。