Study On Ecological Stoichiometric Characteristics In Reed Community Under Different Water-salt Habitats In The Yellow River Estuary

In recent years,with the acceleration of human development and the increasing interference of frequent swing and irregular flow interruption of the Yellow River,the spatial distribution difference of water and salt in the Yellow River Delta has been aggravated,and the change of water-salt conditions will cause changes in the physiological characteristics of wetland vegetation and soil physical and chemical properties in the Yellow River Estuary.As one of the most widely distributed species in the region,Phragmites communis not only has great potential to develop forage resources,but also provides an important ecological role for wetland ecosystems.Therefore,exploring the response characteristics of reed community vegetation-soil system to changes in water-salt conditions will help to further understand the adaptation mechanism of wetland vegetation community to the environment,and also provide a scientific basis for more reasonable utilization and protection of reed in the Yellow River estuary wetland.In this study,the study area was located in the protected area of the Yellow River Delta.According to the influence degree of the Yellow River diversion,we selected three different water-salt habitats as the research area,including the old Yellow River course（OC,the P.australis community in the former Yellow River course abandoned in 1996）,the new Yellow River course（NC,the P.australis community on the new Yellow River course）and the intertidal area(TC,the P.australis communities on the intertidal area（far from the abandoned and current channel but affected by the tides）,aiming to discuss mainly that biomass,carbon（C）,nitrogen（N）,phosphorus（P）concentration and stoichiometric characteristics of P.australis organs（stems,leaves,rhizomes and fibrous roots）and spatial distribution characteristics of soil elements（large elements and heavy metals）in three habitats.The main conclusions show below:（1）In terms of water and salinity conditions,the diversion of the Yellow River has brought significant indigenous impacts on the water and salt conditions in the three study areas.Among them,the soil electrical conductivity and groundwater level（mean value from May to October）followed NC siteNC site and the TC site.And the concentration of Cd showed the order of OC sitegeoindicated that Ni,As and Mo showed high toxicity risks.The EF results showed that Cu,Ni,As,Mo and Hg of the three habitats might stem mostly from anthropogenic sources.According to theΣTUs and TRI,the pollution levels showed the following order:TC site>OC site>NC site.（3）In terms of vegetation characteristics,affected by long-term water and salt conditions,the morphological characteristics of P.australis in the three study areas had significant differences.Among them,the plant height and leaf number of P.australis were in the order of OC site>NC site and TC site.Under the action of flooding,the stem diameter,leaf width and leaf length of reed were in the order of NC site>OC site and NC site,while the density of reed was opposite.At the same time,the nutrient allocation strategies of reed organs in different habitats were also different.The leaf N,C and P contents of P.australis were highest in OC site,the leaf N,stem C and rhizome P contents were highest in NC site.The leaf N and stem C and P contents were highest in TC site.The average leaf C(409.48g·kg^-1)and P(1.09 g·kg^-1)contents in the three habitats were lower than national and global average levels,while leaf N contents(21.71 g·kg^-1)was higher than national and global average levels.The mean leaf N:P（20.22）was higher than 16,indicating that the reed growth in the three habitats was limited by P.In general,the Yellow River diversion further affected the accumulation and distribution of soil elements and the growth of plants in the reed community of the Yellow River estuary by changing the soil water and salt conditions.Although the soil heavy metal pollution level in OC site has increased under the influence of many factors,due to the long history of soil formation in the area,the soil nutrient storage was also higher than that in NC site and TC site.At the same time,in the economic yield of P.australis,P.australis will redistribute nutrients in the body through their own compensation mechanism under stress conditions,which help reed to adapt the growth environment in morphology better.Therefore,the differences in biomass per plant among the three habitats were not significant.It can be seen that under the premise of protecting the local ecosystem health,taking the reed community in the Yellow River estuary wetland as the reserve resource of forage raw materials and developing the appropriate technical system are expected to improve the ecosystem service value of P.australis on the basis of more reasonable and scientific utilization of reed resources in the Yellow River Delta.