The Breakwaters Changed The Characteristics Of Plant Communities In The Coastal Wetland Of The Yellow River Delta

Coastal wetlands are a vital part of the global ecosystem and play a unique role in regulating global climate and protecting species genes.The coastal wetlands of the Yellow River Delta(YRD),with sensitive and fragile ecological environments,are facing various problems such as salinization,human disturbance and biological invasion.This study was carried out in the Binzhou Port area of the YRD in order to explored the ecolodical effects of human disturbance on the coastal wetland.One sampling zone(A)was set outside the tidal dam,and four transects(B,C,D,E)were set equidistantly inside the tidal dam.We surveyed the vegetation characteristics and physical and chemical properties of soil on the coastal wetlands.And we analyzed the influences of breakwaters on the plant species composition,structure,diversity,biomass,and plant stoichiometry of the communities.We also outlined the correlations between plant community characteristics and the physical and chemical properties of soil.The TWINSPAN and the ordination PCA and DCCA were employed to examine the main factors influencing the plant community succession and vegetation distribution in the coastal zone of the YRD.This research will providing theoretical basises for ecological restoration and protection of wetlands in the YRD.We exhibited four main results listed as follows.(1)The breakwaters significantly changed the physical and chemical properties of the soil in the coastal wetlands of Binzhou Port.The results indicated that the water content(SWC),available phosphorus content(AP),and salt content(SC)of soils in the seaward side of the breakwaters(investigating transect A)were 26.59%,13.51 mg/kg,and 12.74g/kg,respectively.Those were significantly higher than the SWC(investigating transect B to E:17.32%,16.26%,14.94%,11.73%),AP(investigating transect B to E:9.37 mg/kg,6.76 mg/kg,4.41 mg/kg,5.79 mg/kg),SC(investigating transect B to E:10.06g/kg,10.39g/kg,10.73 g/kg,6.54g/kg)of soils in the landward side of the breakwaters.The soil organic matter content showed significant differences between the seaward(investigating transect A:7.08 g/kg)and landward(investigating transect B to E:10.39 g/kg,8.83 g/kg,8.78 g/kg,8.95 g/kg)side of the breakwaters.(2)The plant community structure and function of the wetlands in the coastal zone of Binzhou Port were relatively simple,and were significantly changed by the breakwaters.The plant species belonged to 11 species in 6 families of 10 genera,and halophytes were dominant species which included 5 species in 6 families of 5 genera.The biomass of dominat shrub(Tamarix chinensis)in the plant community was 0.09 kg/m~2?2.5 kg/m~2.From seaward side to landward side of the breakwaters,the plant community changed from the Suaeda salsa community to the Tamarix chinensis-Phragmites australis community.The results indicated that the Margalef index(R),Shannon-Weiner index(H)and the biomass of Tamarix chinensis in the seaward side of the breakwaters(investigating transect A)were0.15,0.26 and 0.16 kg/m~2,which was significantly lower than the R(investigating transect B to E:0.39,0.38,0.49,0.51),H(investigating transect B to E:0.77,0.68,0.78,1.07);T.chinensis biomass(investigating transect B to E:0.35 kg/m~2,0.20 kg/m~2,0.43 kg/m~2,0.49kg/m~2)in the landward side of the breakwaters.And the Simpson index(D)in the seaward side of the breakwaters(investigating transect A)were 0.16,which was lower than the D(investigating transect B to E:0.39,0.36,0.39,0.57).In the landward side of the breakwaters,the plant community characteristics generally showed an increasing trend as the distance from the breakwaters increased.The Sorensen index(Cs),Jaccard index(Cj)and Cody index(?_C)showed that the communities between the seaward and landward sides of the breakwaters had relatively small similarities,fewer common species,and large habitat differences.(3)The dam has changed the ecological stoichiometric characteristics of the dominant shrubs in the plant community.The results indicated that plant foliar C:N(investigating transect A to E:14.27,17.21,16.45,17.56,20.93),C:P(investigating transect A to E:207.84,252.94,245.42,259.06,257.60),which showed that the ability of plants in the seaward side of the breakwaters to assimilate carbon was significantly lower than that in the landward sides of the breakwaters.Plant foliar N:P(investigating transect A to E:14.54,14.60,14.93,14.77,12.71)showed that the restriction of nutrient elements had changed from the co-restriction of N and P seaward side of the breakwaters to a single restriction of N in the landward side of the breakwaters.The RDA classification showed that C:N and C:P of Tamarix chinensis leaves were strongly negatively correlated with soil salt content,and N:P was strongly positively correlated with soil salt content,which shows that the salt content was the main factor affecting the stoichiometry of T.chinensis.(4)TWINSPAN classification and principal component analysis(PCA)were used to classify and rank the plant communities in Binzhou Port.Through TWINSPAN classification and actual investigation,the plant communities of Binzhou Port were divided into four categories:Suaeda salsa,Tamarix chinensis,Tamarix chinensis-Phragmites australis-Suaeda salsa and Tamarix chinensis-Cynanchum chinense-Phragmites australis.The PCA ranking was consistent with the TWINSPAN classification results.The soil factors were sorted by DCCA,and the community plots and species were well correlated with environmental factors.The first ordinal axis of DCCA mainly reflected the change gradient of soil salinity;the second sort axis mainly reflected the change gradient of soil available phosphorus.The PCA results of 16 soil factors showed that the SC and AP were the key ecological factors which determined the position of the community and the composition of the community species.