Changes in the structural and functional diversity of macrophyte communities along an acidity gradient in softwater lakes

We present a new approach to the diversity of macrophyte communities based on species richness (S), Simpson's diversity index (SD), Rao's functional diversity (FD), functional attribute diversity (FAD) and the share of life history traits along a gradient of acidity in softwater lakes. On the basis of 10,800 cover-plant samples (squares with an area of 0.1 m2) collected from 241 sections of the bottom (depth belts) of 38 lakes, four communities were identified using the TWINSPAN algorithm: moss carpet (median water pH 4.7), isoetids with acidophytic mosses (pH 5.5), isoetids with neutrophytic mosses (pH 6.3) and neutrophytic vascular plants with charophytes (pH 7.1). Along a gradient of increasing pH, the diversity of communities increases and the species composition and share of life history traits are subject to significant changes. Evergreen, plagiotropic and unanchored plants with small, thin leaves (mosses) are replaced by evergreen, rosette forms (isoetids), which are replaced by non-evergreen charophytes and broadleaf vascular plants, especially pondweeds, in addition to an increasing fraction of plants with generative reproduction. A strong relationship was found between plant traits (leaves and shoots) and environmental factors (pH and calcium content). The regulator of diversity in macrophyte communities is the calcium concentration in water.