Interactive Effects Of Nitrogen Addition And Groundwater Level On The Growth Of The Wet Plant Carex Thunbergii In The Lakes Connecting The Yangtze River

Studying the effects of groundwater level changes and nitrogen deposition on plant functional traits is essential to reveal the response and adaptation pattern of wetland plants to environmental changes.In this paper,a field study was conducted to investigate the influences of groundwater level(I: low water level;II: middle water level;III: high water level)and nitrogen addition [N-(N reduction);N0(blank control);N1(low nitrogen);N2(medium nitrogen);N3(high nitrogen)](where in the nitrogen reduction treatment is added in terms of carbon element content The rest of the treatments are based on the amount of nitrogen added),including the species richness,aboveground biomass,soil and leaf nutrient content and root morphological parameters of Carex thunbergii.We achieved main result as follows:1.The results of two-factor analysis of variance showed that the groundwater levels mainly affected species richness,above-ground biomass and root morphological indicators and soil nutrient content and leaf carbon content(P<0.05),while nitrogen addition influenced soil nutrient content,root specific root length,specific surface area,and tissue density and soil nutrient content and leaf carbon content(P<0.05)to a significant level.Meanwhile,the interaction between groundwater level and nitrogen addition had a significant effect on the specific root length and average diameter and leaf carbon content of C.thunbergii(P<0.05),with groundwater level dominated these variables,The response of underground indicators to water level and nitrogen addition is stronger than that of above-ground indicators.2.As for groundwater level,it reduced the above-ground biomass,root specific root length and tissue density,but increased the root diameter and specific surface area of C.thunbergii,when compared with lower groundwater treatments(P<0.05).Under N0 treatment,compared with low water level,the aboveground biomass,root specific root length and tissue density of C.thunbergii decreased by 97.6%,46.1%,and 86.1%,respectively,while mean root diameter and specific surface area increased by 326.1%,198.5%.3.As for nitrogen addition the specific root length and specific surface area of C.thunbergii decreased at lower rates of nitrogen addition but increased at higher rates,and tissue density showed a contrast trend,depending the rates of nitrogen used.Under high water level conditions,compared to N0 treatment,the root length and specific surface area of C.thunbergii roots were reduced by 36.1% and 41.8%,respectively,and the difference was significant,while there was no significant difference between N0 and N3 treatment.On the contrary,under high water level conditions,compared with N0 treatment,the root tissue density of C.thunbergii increased by 182.4%(P <0.05),but there was no significant difference between N0 and N3 treatments.4.With the increase of water level,the soil carbon and nitrogen content and stoichiometry ratio of C.thunbergii soil under different nitrogen application gradients showed the same increasing trend,and the minimum values of soil carbon and nitrogen content and stoichiometry of C.thunbergii soil were obtained at low water levels There is a significant difference between the low water level and the middle water level under all nitrogen treatments(P<0.05).With the increase of nitrogen application gradient,the soil carbon and nitrogen content and its stoichiometry ratio at the different water level gradients showed the same trend of first increase and then decrease.There were significant differences in soil carbon and nitrogen content and stoichiometry between the N0 treatment and the other four treatments(P<0.05).Studies have shown that the effects of increased groundwater level and nitrogen addition on the aboveground biomass and specific root length of C.thunbergii are offsetting each other,which reflects the stress effect of increasing soil moisture on the growth of C.thunbergii The effects of addition on root specific surface area and root tissue density showed a synergistic effect,revealing changes in nutrient acquisition strategies of C.thunbergii under water level stress.