Phragmites australis makes valuable floating mat biotopes under oligotrophic conditions

Abstract

To understand the mechanism of how Phragmites australis makes valuable floating mat biotopes under oligotrophic conditions, we investigated the environmental (water chemistry) and vegetational characteristics (growth, plant species richness, and floristic composition) of a floating mat consisting of three main mat-forming species with a zonal distribution (P. australis on the land side of the floating mat, Zizania latifolia on the middle area, and Typha angustifolia on the water side). Although they showed relatively low growth in the floating mat, compared to those in land-based wetlands, P. australis grew better than other mat-forming species in terms of shoot height and biomass production. Specifically, P. australis made more below-ground parts (593 ± 38 g/m2) than other mat-forming species (Z. latifolia, 100 ± 10 g/m2; T. angustifolia, 167 ± 8 g/m2) and more companion species were found in P. australis-dominated plots (8.5 ± 1.0 species/m2) than other plots (Z. latifolia-dominated plots, 2.7 ± 0.6 species/m2; T. angustifolia-dominated plots, 1.0 ± 0.0 species/m2). The larger amount of below-ground P. australis parts could contribute to thicker and denser mat structures, possibly providing more favorable habitats for neighboring plant species, thus facilitating more companion species within the P. australis-dominated area of the mat.