The Effect Of Flooding Duration And Underwater Light Intensity On Wetland Plant Functional Traits And Biomass In Poyang Lake

Global climate change and human activity have altered the flooding regime of wetlands.Flooding regime can affect wetland plant growth through direct pathway(flooding stress)and indirect pathway(underwater light intensity,soil nutrient).Wetland plants can adapt to flooding duration by functional traits.However,scaling the responses of wetland plants to changes in flooding duration is still challenging.Moreover,the decrease of underwater light intensity directly and indirectly affects the growth of wetland plants during flood period.However,the effect and underlying mechanism of underwater light intensity on wetland plants growth are still unclear.To examined the effect of flooding duration on the functional traits of wetland plants at different scales(intra-and inter-species),we established transect samples along the lakeshore meadow in Poyang lake,along flooding duration gradient.We measured 11 different functional traits,and tested the effects and relative importance of flooding duration and soil nutrient on leaf N and P stoichiometry.We designed a laboratory experiment to test the effect of light intensity on wetland plants growth,and designed a field experiment to test the effect of shading on wetland plant community.The main research results are as follows:1)At intra-species level,flooding duration significantly affected the functional traits of Carex cinerascens and Phalaris arundinacea,and showed different effects between the two species.However,only leaf N content had a significant relationship with species' average flooding duration at inter-specific level.Of the 11 plant functional traits,the responses of 5 functional traits to flooding duration significantly differed between intra-species and inter-species levels.2)Flooding duration affected leaf N and P stoichiometry mainly through direct pathway at intra-species and inter-community level,rather than indirect pathway via soil nutrient stoichiometry.Flooding duration significantly affected the leaf N and P stoichiometry at the intra-species and inter-community level,and had no significant effect at inter-species level.The change rates of leaf N and P stoichiometry at intra-species level significantly correlated with the hydrological niche of species.Intra-species variation had lower contribution than species turnover to variations in community leaf nutrient stoichiometry.3)At the individual level,the changes of underwater light intensity and flooding treat had significant effects on C.cinerascens growth,and the two effects were additive.With the underwater light intensity decreasing,potential photosynthetic rate and chlorophyll content decrease.At the non-flooding period,the aboveground biomass and total leaf length of C.cinerascens can be recovered,belowground biomass significantly decreased.At the community level,the decreased underwater light intensity decreased the aboveground biomass of C.cinerascens community and resulted in the significant decrease of aboveground biomass.With the increase of recovery time,the negative effect of the decrease of light intensity on biomass turned to be not significant.Above all,the response of wetland plant functional traits to flooding duration varied with different organizational levels(intra-species,inter-species,inter-community),but the responses at different organizational levels are linked.The decrease of underwater light intensity can aggravate the stress effect of flooding on wetland plants.