Environmental determinants of aquatic plant diversity differ between growth forms and range sizes

Aquatic plants are fundamental for aquatic ecosystems. Understanding variations in geographic patterns of aquatic plant diversity across growth forms is important for conservation and restoration of aquatic ecosystems. Environmental drivers, including climate, climate heterogeneity, water chemistry, habitat availability and geodiversity, could influence aquatic plant diversity and species composition across communities, yet their relative impacts remain controversial. Here, we examined geographic patterns and drivers of species richness of Chinese aquatic plants with different growth forms. We compiled distributions of 656 aquatic plant species in China at 50 × 50 km² resolutions, and estimated richness patterns for species with different growth forms (i.e., helophyte, emergent, floating-leaved, free-drifting and submerged) and range sizes. Hierarchical partitioning analysis was employed to evaluate the independent effects of different environmental drivers on species richness. The Sørensen dissimilarity index and Multiple Matrix Regression with Randomization were used to compare the relative effects of environment and dispersal limitation on species dissimilarity between grid cells. Overall species richness was highest in northeastern and southern China, although species richness patterns varied across growth forms. Among environmental drivers examined, climate was the key determinant of the species richness of helophyte, emergent, floating-leaved and free-drifting plants, while habitat availability and water chemistry best explained the richness of submerged species. The richness of narrow-ranged species was dominated by climate, while the strongest determinant of wide-ranged species richness varied across growth forms. Our study mapped the species richness patterns of aquatic plants in China and indicated that the relationship between aquatic plant richness and environment significantly differed between growth forms and between wide-ranged and narrow-ranged species. These findings indicate the necessity of distinguishing growth forms in studies related to aquatic plants, and suggest that future climate change might threaten the distribution of narrow-ranged aquatic plants.