Temporal And Spatial Variation Of Soil Enzyme Activity At Typical Lakeshore Wetland Of Poyang Lake

Soil enzymes are important components in biogeochemical processes of wetland ecosystems.Study in temporal and spatial variation of soil enzyme activities is of great significance for revealing the biogeochemical processes and their responses to global changes in wetlands.However,the current research on temporal and spatial variations of soil enzyme activities is mainly carried out in wetlands with minor water level fluctuations.With global changes and human activities,the global seasonally flooding wetlands are rapidly expanding,which may significantly change soil enzyme characteristics of wetlands.The spatial and inter-annual variations,and their influencing factors of soil enzyme activities in seasonally flooding wetlands are still unclear.In this study,we investigated the spatial and inter-annual variations of soil enzyme activities and stoichiometry at the lakeshore wetland of Poyang Lake.Additionally,inter-annual differences of the temperature sensitivity of soil enzyme activities were explored in the lakeshore wetland of Poyang Lake.Firstly,we selected four typical sub-lakes in Poyang lake(Dong lake,Baisha lake,Beng lake and Dahuchi lake).The activities and stoichiometry of soil enzymes were compared at different soil depths(0-10 cm,10-20 cm,and 20-30 cm)and at different elevations.Then,based on a long-term monitoring plot of Dong lake,inter-annual differences in the activities,stoichiometry,and temperature sensitivity of soil enzymes from 2019 to 2021 were analyzed.The soil enzymes measured in this study includedβ-glucosidase and phenoloxidase(related to carbon cycle),N-acetylglucosaminidase(related to nitrogen cycle),and phosphatase(related to phosphorus cycle).This study aims to illustrate the basic pattern of carbon,nitrogen,and phosphorus biogeochemical cycles with flooding effects in the future.Our results provide a basis for improving terrestrial system models and protecting seasonally flooding wetlands.The main findings were as follows:(1)Sub-lake type had a significant effect on the activities of the four soil enzymes,and the activities of these four enzymes generally were higher in semi-closed lakes(Baisha lake and Dahuchi lake)than in the connected lakes(Dong lake and Beng lake).Elevation had a significant effect on β-glucosidase and phosphatase activities.The trend of β-glucosidase activity at different elevation was light beach transect > the carex transect > the emergent plant transect.The phosphatase activity was the highest in the light beach transect,followed by the carex transect,and lowest in the emergent plant transect.Phenoloxidase activity was gradually decreased with increasing depth.The spatial differences of soil enzyme activities were mainly affected by soil water content and organic matter content.(2)Sub-lake had significant effects on the BG: NAG,BG: PHOS,and NAG:PHOS.The BG: NAG in Beng lake was significantly lower than that in Dong lake,Baisha lake,and Dahuchi lake.The BG: PHOS in Dong lake was significantly higher than that in Beng lake,Baisha lake,and Dahuchi lake.The NAG: PHOS in Dahuchi lake was significantly lower than that in Dong lake,Beng lake,and Baisha lake.The BG: PHOS was highest in the emergent plant transect,followed by the light beach transect,and lowest in the carex transect.Depth had a significant effect on the BG: NAG,and the BG: NAG gradually decreased with the increase of depth.Soil enzyme stoichiometry were mainly influenced by soil nutrient and element stoichiometry.(3)From 2019 to 2021,the activities of the four soil enzymes were the highest in the wet year(2021),followed by the normal year(2020),and the lowest in the dry year(2019).Soil enzyme activities in these three years were significantly affected by vegetation features and soil nutrient content.The BG: PHOS in the wet year and the normal year were significantly greater than that in the dry year.There were no significant differences in the BG: NAG and NAG: PHOS among the three years.Soil enzyme stoichiometry in these three years was significantly affected by the vegetation features and soil element stoichiometry.(4)The temperature sensitivity of β-glucosidase and N-acetylglucosaminidase activities ranged from 2.59 to 3.70 and 2.16 to 3.37 from 2019 to 2021,respectively.Both temperature sensitivities of β-glucosidase and N-acetylglucosaminidase were the highest in 2019(a dry year),followed by 2020(a normal year),and the lowest in2021(a wet year).The temperature sensitivity of phenoloxidase activity varied from1.48 to 2.45,and was the highest in 2021(a wet year),followed by 2019(a dry year),and the lowest in 2020(a normal year).The temperature sensitivity of phosphatase activity varied from 2.37 to 2.88,and was the highest in 2019(a dry year),followed by 2021(a wet year),and the lowest in 2020(a normal year).The temperature sensitivity of soil enzyme activities in these three years was mainly affected by soil p H,vegetation features,and soil nutrient content.