Testing mechanisms underlying responses of plant functional traits to flooding duration gradient in a lakeshore meadow

Abstract

Flooding duration is a major factor determining wetland plant growth and community composition. While there have been extensive studies on how direct effects of flooding duration on plant functional traits, very few have tested the indirect effects on these traits, including those arising from competition. We hypothesized that there would be a shift in importance of competition ability and flooding tolerance to functional traits along the flooding duration gradient. We investigated plant functional traits along a flooding duration gradient for two-dominant wetland plant species (Carex cinerascens and Phalaris arundinacea) in a lakeshore meadow of Poyang Lake, China. We found that these two species tended to have different strategies to adapt to flooding stress. P. arundinacea tended to adopt escape strategy with high growth rate (e.g. greater height, specific leaf area, and leaf N and P content) at longer flooding duration, while C. cinerascens tended to adopt more quiescence strategy, with only 5 of 13 of its traits showing a significant response. With shorter flooding duration, both species tended to have lower leaf N and P content, indicating greater nutrient limitation. Meanwhile, relative abundance of C. cinerascens with relatively higher belowground nutrient competition ability (i.e. greater root/shoot biomass ratio) decreased with flooding duration. These results suggest that belowground competition intensifies at shorter flooding duration, because of increased nutrient limitation with increased productivity. Therefore, our study indicates that both flooding stress and nutrient competition could affect plant functional traits along a flooding duration gradient.