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.