Variation in the Biomass of Phragmites australis Across Community Types in the Aquatic Habitats of the Middle Volga Valley

Species composition and biomass are key indicators of vegetation performance. While Phragmites australis is extensively studied worldwide, data on its communities and biomass in natural habitats are limited in the European part of the Russian Federation. This study examines P. australis-dominated communities and their biomass in wetlands along the Middle Volga River. P. australis was either the dominant or co-dominant species in seven community types. Their seasonal maximum aboveground biomass correlated with plant projective cover, being highest in Schoenoplecteto lacustris-Phragmitetum australis (mean 1.7 kg m−2), with nearly 100% cover, and lowest (0.5 kg m−2) in Spirodelo-Phragmitetum australis, with 50% cover. Compared with communities dominated by Glyceria maxima, Schoenoplectus lacustris, and Typha latifolia, those of P. australis had the highest seasonal maximum aboveground biomass in running waters (mean 1.32 kg m−2) but the lowest in standing waters of the Kuibyshev Reservoir (mean 0.70 kg m−2), likely reflecting nutrient availability. A similar pattern was observed for the dominant species alone. The mean belowground biomass of P. australis was 1.9 kg m−2, with a belowground/aboveground ratio of 1.5. Similar values were found for S. lacustris and T. latifolia. The community types and biomass values align with those found in other European regions with warm temperate climates.