Plant Community Succession And Driving Force Analysis In Estuary Wetland Of The Yellow River Delta

The wetland as an important part of global ecosystem,play an irreplaceable role in maintaining regional ecosystem stability,species genetic protection,resource utilization and even the impact of global climate change.Plant community succession is the symbol and important content of wetland evolution.Strengthening the study of wetland plant community succession and its driving force is the core of wetland ecosystem restoration research,and is also an important basis for the development and utilization of wetland ecological resources.Based on the sample survey of wetland vegetation in the Yellow River Delta and the analysis of soil physical and chemical properties,this study studied the species composition,species diversity and the relationship between wetland vegetation community and environmental factors,determined the community composition and succession process of wetland vegetation in the Yellow River Delta,explained the driving factors affecting the succession of plant communities,and formulated wetland protection decision-making and production for the region.The state restoration scheme provides a scientific basis.Through the analysis of this study,the main conclusions are as follows:（1）The composition of plant communities in estuarine wetlands of the Yellow River Delta is simple,mostly halophytes belonging to 17 genera and 7 families.With Shannon-Wiener index（0.62,1.38,1.80）,Simpson index（0.43,0.64,0.78）,Margalef index（0.09,0.44,0.82）,Pielou index（0.90,0.89,0.76）gradually increased,and species showed a trend of spatial distribution from Suaeda salsa community to Tamarix community and then to Phragmites australis community.Jaccard index and Jaccard distance showed that there were more common species in Suaeda salsa community and Tamarix Tamarix community,and the differences between species were small,the degree of habitat isolation was low,and the rate of species replacement was slow.Tamarix chinensis and Phragmites australis communities have the smallest similarity and the largest interspecific difference,and the habitat is highly isolated by species,and the rate of species replacement is faster.Succession process includes:○1 Suaeda salsa-Tamarix tamarix-Phragmites australis○2Suaeda salsa-Phragmites australis.（2）With the decrease of soil salinity,the community successed from Suaeda salsa to Tamarix Tamarix to Phragmites australis,and most of the soil salt ions in Suaeda salsa and Tamarix Tamarix communities had the characteristics of surface accumulation,while the distribution in the Phragmites australis community was relatively uniform.The correlations among salinity indices of different communities were different,but the total salt（TS）of soil in three plant communities was significantly correlated with chloride ion（Cl^-）（P<0.01）,and the Cl^-content was much higher than any other ion content,which was the main effective salt separator in soil.Variability analysis showed that in horizontal direction,except sulfate ion(SO₄^2-（1.31）)in Tamarix Tamarix community,magnesium ion(Mg²⁺（1.80）),Cl^-（1.29）and TS（1.06）in Phragmites australis community belonged to strong variation,the other ions and TS coefficient of variation belonged to moderate intensity variability.In vertical direction,except for Mg²⁺（0.08）in Phragmites australis community,the other ions and TS showed moderate intensity variation.In the two-dimensional direction,the coefficient of variation of TS showed that Tamarix chinensis Community>Suaeda salsa Community>Phragmites australis community.With the increase of soil depth,the sodium adsorption ratio of the three plant communities increased first and then decreased,and the maximum values（6.13,4.52,2.73）appeared in the soil layer of 10-20 cm.（3）In the estuarine wetland of the Yellow River Delta,soil nutrients are deficient,and the contents of soil carbon（C）,nitrogen（N）,phosphorus（P）are 5.05,0.42 and 0.54 g/kg in Suaeda salsa community,5.05,0.50 and 0.58 g/kg in Tamarix Tamarix community,15.82,0.67 and 0.66 g/kg in Phragmites australis community,and the variability belongs to moderate intensity（Suaeda salsa,Tamarix tamarix）,and weak variability（Phragmites communis）.Soil stoichiometric characteristics showed that C:N of Suaeda salsa,Tamarix Tamarix and Phragmites australis communities were 12.04,10.03 and 23.67,respectively,which were less than 25.Soil organic matter decomposition rate was higher than accumulation rate.The wetland ecosystem in the Yellow River Delta was facing the risk of ecological degradation.N:P was 0.77（Suaeda salsa）,0.87（Tamarix tamarix）and 1.02（Phragmites australis）in turn less than 14.Consequently,nitrogen is limited nutrient factor to the growth of plant in study area,and the deficiency of nitrogen element should be alleviated through appropriate ways.Soil water content is the main microclimatic factor affecting the succession of plant communities in estuarine wetlands of the Yellow River Delta.（4）Redundancy analysis is a scientific and effective method in analyzing the impact of a single environmental factor on the object of study.It clearly and intuitively shows the interpretation of environmental factors on the object of study on the basis of two-dimensional graphs.Redundancy analysis showed that TS,soil water content（WC）and available nitrogen（AN）explained 62.1%,30.0%and 21.0%of the community succession respectively,which were the main factors affecting the plant community succession in the estuarine wetland of the Yellow River Delta,and TS was the key factor.