Characteristics Of Wetland Plant Community And Its Relationship With Environmental Factors In Nianchu River Basin

Wetland ecosystem is a habitats transition zone between terrestrial and aquatic ecosystems,with characteristics of both ecosystems and high biodiversity.At present,there are few studies on swamp wetlands in Tibet.In this paper,the characteristics of the flora,plant community characteristics and their influencing factors,the relationship between plant diversity and environment,and the characteristics of interspecific associations and ecological niches of plant were studied in the swamp wetlands of the Nianchu River Basin as the research site.Fourteen wetlands were selected in the Nianchu River Basin with sample size of 2m×2m for meadow vegetation and 5m×5m for buckthorn shrubby wetlands,a total of 49 samples.Plant species,cover,height and abundance were recorded in each sample.Three soil samples of 0-10 cm were collected from each sample and combined into one large sample.The soil samples were dried and sieved,and the soil water content,soil nutrients(total nitrogen,hydrolysable nitrogen,total phosphorus,available potassium and available phosphorus)were determined for each sample.TWINSPAN classification was used to classify the plant communities of the wetlands;the plant communities were analysed by using DCA and the relationship between plant distribution and environmental factors was studied by using canonical correspondence analysis(CCA).The generalized additive model(GAM)was used to regress the relationship between plant diversity indices and environmental factors.Ecological niche characterization of dominant plant species were analysed using Levins method for calculating niche width and Pianka index for calculating niche overlap.The interspecific association coefficient(AC)and Ochiai index were used to analyze the interspecific association relationships within the plant community.The results showed as follow:(1)A total of 135 plant species,belonging to 84 genera and 35 families,were recorded in wetlands in the Nianchu River Basin.The composition of families is dominated by monospecific families and small families,and the composition of genera is dominated by monospecific genera.The geographical distribution types of families are divided into four types and three subtypes,mainly the widespread type.The geographical distribution types of genera are divided into 10 types and 6 subtypes,mainly the temperate distribution type.The plant life of wetland in the Nianchu River Basin is mainly herbaceous,among which perennial herbs are the most abundant.The plant resource type of wetland in the Nianchu River Basin is in rich mainly medicinal,ornamental and nectar plants.(2)The results of TWINSPAN classification analysis showed 49 plant samples divided into 7 groups including Leontopodium pusillum+ Pedicularis kansuensis(ASS),Ranunculus nephelogenes+Epilobium palustr(ASS),Parnassia trinervis + Euphrasia regelii subsp.Kangtienensis(ASS),Kobresia humilis + Kobresia pygmaea(ASS),Blysmus sinocompressus + Potentilla anserine(ASS),Potamogeton pusillus + Eleocharis valleculosa(ASS)and Potentilla anserina + Lancea tibetica(ASS).The plant communities of the Nianchu River basin wetlands were classified into four community types,including wet meadow community,scrub meadow community,aquatic plant community,and marshy community,by DCA sequencing analysis.The distribution pattern of Nianchu River marshy wetland plant communities is mainly influenced by six environmental factors: soil water content,total nitrogen,hydrolysable nitrogen,altitude,longitude and latitude.(3)The Shannon index of the plant community in the wetland of the Nianchu River Basin showed a monotonic increasing relationship with soil water content,and a single peak pattern relationship with total nitrogen and hydrolysable nitrogen;there was no significant relationship between the Shannon index and total phosphorus,available potassium and effective phosphorus.The Simpson index of plant community increased with the increase of soil water content and hydrolysable nitrogen,but there was no significant relationship with total phosphorus,total nitrogen,available potassium and available phosphorus.There was no significant relationship between the Pielou evenness index and soil nutrients(total nitrogen,total phosphorus,hydrolysable nitrogen,available potassium and effective phosphorus)and soil water content.The species richness increased with increasing soil water content,but it showed a single-peaked trend and then decreasing with total nitrogen and hydrolysable nitrogen.While there was no significant relationship with total phosphorus,available potassium and available phosphorus and species richness.There is a single peak pattern relationship between Shannon index and altitude.Shannon' s index increased linearly with longitude while it decreased with increasing of latitude.There is a single peak pattern relationship between Simpson index and altitude.And the Simpson index and longitude showed a monotonic increasing relationship,and there is monotonic decreasing relationship between the latitude and the Simpson index.The Pielou evenness index showed a slowly decreasing trend with altitude.There is a single peak pattern relationship between Pielou evenness index and latitude and there was no obvious relationship between the Pielou evenness index and longitude.The species richness and altitude showed an increasing-decreasing-increasing trend.The species richness and longitude showed a monotonic increasing relationship,and the species richness and latitude showed a monotonic decreasing relationship.(4)The niche width of the dominant species in wetlands of the Nianchu River Basin varied greatly,among which the niche width of Potentilla anserina and Blysmus sinocompressus was the largest,and the niche width of Astragalus strictus and Eleocharis valleculosa was the smallest.The niche overlap of the dominant species ranged from 0 to 0.795.The number of positively associated species pairs was higher than the number of negatively associated species pairs,and the interspecific associations were relatively strong,indicating that the plant community of Nianchu River Basin marsh wetland was in a stable state.