Effects of nitrogen and phosphorus inputs on photosynthesis of three emergent macrophytes in a freshwater wetland

Abstract

The excessive inputs of nitrogen (N) and phosphorus (P) into water bodies lead to eutrophication, resulting in significant alterations in nutrient cycles and wetland productivity. However, how N and P inputs regulate leaf functional traits and thus the photosynthesis of emergent macrophytes remains largely unexplored. Based on a field experiment simulating aquatic eutrophication in a freshwater wetland, this study was conducted to examine the influences of N and P inputs on leaf functional traits and the net photosynthetic rates of three dominant emergent macrophytes including Phragmites australis (P. australis), Sagittaria trifolia (S. trifolia), and Alisma plantago-aquatica (A. plantago-aquatica). The results showed that N input increased the net photosynthetic rates of P. australis and A. plantago-aquatica by 5.37 % and 14.7 %, but did not affect that of S. trifolia. Phosphorus input enhanced the net photosynthetic rate of P. australis by 3.20 %, but had no effects on the other macrophytes. Elevated leaf N content, leaf thickness and specific leaf area primarily drove the increases in photosynthesis of P. australis under eutrophication. By contrast, the stimulated chlorophyll content predominantly explained the enhanced photosynthetic rate of A. plantago-aquatica. In addition, the increased photosynthetic rates of emergent macrophytes positively contributed to plant biomass and ecosystem CH₄ emissions, indicating the importance of plant photosynthesis in driving wetland C source-sink functions. Our findings highlight the crucial roles of leaf functional traits in regulating plant photosynthetic process, and can provide new insights into understanding plant photosynthesis and C cycling feedback under aquatic eutrophication.