Effects Of N And P Supply Condition On Plant Community Structure And Stoichiometric Characteristics Of Costal Wetland

Human activities have significantly altered the environmental nitrogen(N)and phosphorus(P)status through changing both overall supply level and N:P supply ratio,and may further influence structure and function of ecosystems.To explore the effects of N and P supply condition on plant community structure and stoichiometric characteristics of coastal wetland,a field manipulation experiment combined three overall nutrient supply levels(Low,Medium,High)and three N:P supply ratios(5:1,15:1,45:1)was conducted in the Yellow River Delta from 2015 to 2017,in which the overall nutrient supply was defined as the geometric mean of the supplied amount of N and P.The soil properties,plant community structure and community stoichiometry were tested.The effects of N and P supply condition on these characters were analyzed,and the relationship among these characters were explored as well.The aim of this research was to provide references for ecological conservation and restoration of coastal wetland in the Yellow River Delta.The results indicated that:(1)Soil total N,total P and available-nutrients concentration under the treatment of fertilization were increased in this study.Soil pH had no significant responses to the variations of N and P supply status.However,soil conductivity was significantly influenced by overll nutrient supply level,with highest at low overall supply level.In contrast with total nutrients,both supply level and supply ratio significantly affected the concentration of soil available-nutrients.With the rise of overall supply level,the soil inorganic N concentration and the available P concentration increased.Moreover,with the rise of N:P supply ratio,the concentration of soil inorganic N increased while which of available P decreased significantly.Therefore,soil available-nutrients concentration were significantly positively correlated with the input of the corresponding elements.(2)The competitive and coexistence relationships among dominant species under the change of N and P supply condition were changed,which mainly determined the response of plant community structure in the Yellow River Delta.Variations of relative supply of N and P had different effects on dominant species in the study area.In contrast with Tripolium vulgare and Cynanchum chinense,both overall supply level and N:P supply ratio significantly influenced the importance values of Suaeda glaucar.Meanwhile,overall supply level had significant effect on the importance values of Phragmites australias and Suaeda salsa.The species diversity under the treatment of fertilization was mainly affected by the changes of the importance values of S.glauca and S.salsa.The species diversity was highest at medium nutrient level,which was determined by two factors: the importance values of S.glauca was highest at high nutrient level and the importance values of S.salsa was maximal at low nutrient supply.Meanwhile,the biomass of plant community was mainly determined by the biomass of S.glauca.With the rise of overall supply level or N:P supply ratio,the biomass of plant community and S.glauca increased significantly.Moreover,the responses of importance values of dominant species,species diversity and biomass to variations of relative supply of N and P were different between 2015 and 2017,suggesting that the effects of N and P supply condition on plant community structure of coastal wetland in the Yellow River Delta were also mediated by air temperature,precipitation and other natural conditions.(3)With N and P supply status changing in this study,C concentration in plant community varied least compared with N and P concentration.As for N and P concentration,both overall supply level and N:P supply ratio had significantly effects on each of them in 2015 and 2017,while the overall supply level affected more.With the rise of N and P supply level,the concentration of corresponding elements increased respectively while C:N and C:P decreased.Moreover,N:P depended most on the N:P supply ratio.With the rise of N:P supply ratio,N:P increased significantly.The changes of C:N and N:P between 2015 and 2017 were analyzed,which indicated that the nutrient limitation in study area gradually transformed from N limitation to P limitation.(4)With the rise of soil inorganic N and available P concentration,N and P concentration in plant community increased significantly while C:N and C:P decreased significantly.Meanwhile,with the rise of N concentration or the decline of C:N,C:P in plant community,the biomass of community increased significantly while Pielou index declined significantly.Both species richness and Shannon-Wiener index were positively correlated with C:N.In conclusion,higher N concentration or lower C:N,C:P in plant community were often corresponded to the higher biomass and lower species diversity in this study.