Study On Plant Community Characteristics Of Alpine Swamp Wetlands In Lhasa River Basin

The swamp wetland as a transitional area between aquatic habitat and dry land is rich in biodiversity and has various important ecological values.At the present,there are few studies on swamp wetland in Tibet.In the present study,the swamp wetland(altitude range from 3641m?4904m)in the Lhasa River Basin as the research area,the floristic characteristics,plant community structure and their influencing factors,the relationship between plant diversity and the environmental variables,and interspecies association in the plant community and niche characteristics of swamp wetland plant were studied in the study area.A total of 10 swamp wetlands were selected as the sample plots and at each plot set11 samples,1×1m for aquatic vegetation and meadow vegetation,and 2×2m for shrub meadow vegetation,110 samples in total.The plant species,coverage,height,abundance were recorded in each sample and other micro-environmental information recorded as well.3 soil sample of 0-10 cm depth were taken in each sample and composed into 1 sample.The nutrient content(hydrolysable nitrogen,total nitrogen,total phosphorus,available phosphorus and available potassium)of each soil sample was determined after air drying and sieving.Cluster analysis was used to classify plant association as well as the Detrend Correspondence Analysis(DCA)was applied to ordinate the plant communities in the swamp wetlands.Canonical Correspondence Analysis(CCA)was sued to detect the relationship between the distribution pattern of plant and environmental factors.The singlefactor variance method was applied to analyze the difference of plant diversity and richness index of swamp wetlands at different altitudes.The regression analysis was used to analyze the relationship between plant diversity,richness index and environmental factors.Shannon-Wiener niche width index and Pianka index were applied to analyze the niche characteristics of plant species in community.The interspecific association coefficient(AC)and the Ochiai index were used to analyze the interspecies association of plant community.The results showed as follow.(1)A total of 212 species,belonging to 128 genera and 48 families,were recorded at the 10 swamp wetlands in the Lhasa River Basin.Among them there were 163 species of dicotyledonous belonging to 98 genera and 39 families,and49 species of monocotyledonous belonging to 30 genera and 9 families.The plant life form of swamp wetland is dominated by perennial herb followed by annual herb.The single species families and small families constitute the main body of seed plant family in the swamp wetland and the single species genus are the main body of seed plant genus of the swamp wetlands in the study area.The floristic characteristics of plant family consisted of 5 distribution types and 3 subtypes and dominated by the Cosmopolitan type with 34 families and accounting for 70.83%of the total number of families.The floristic characteristics of the genus is composed of 11 distribution types and 9 subtypes and dominated by Temperate genera including 89 genera and followed by the Cosmopolitan type with 30 genera accounting for 69.53% and 23.44% of the total number of genera,respectively.There are 10 resource types in swamp wetland resource plants of which medicinal plants are the main ones.(2)The result of Cluster analysis showed that the plants in the swamp wetland can be divided into 5 plant associations including Kobresia pygmaea+Kobresia humilis(ASS),Kobresia humilis+Lancea tibetica(ASS),Kobresia tibetica+Potentilla anserina(ASS),Potamogeton natans+Ranunculus tricuspis(ASS),Kobresia tibetica+Potentilla saundersiana(ASS).The result of DCA showed that the plants in swamp wetlands can be divided into 4 plant communities consisting of shrub-meadow plant community,wetmeadow plant community,marshy plant community(mainly distributed at between the wetmeadow and aquatic habitat)and aquatic plant community.CCA analysis showed that soil moisture,total nitrogen,available phosphorus,and altitude,latitude and longitude are main influencing environmental variables of plant community distribution pattern in the study area.(3)The regression analysis founded that there are U-shaped changing trends in the relationships between the plant species diversity(Shannon-Wiener diversity index,Simpson diversity index),richness(Magalef richness index)and altitude,latitude,longitude and soil hydrolysable nitrogen in the swamp wetland.The plant species diversity and richness linearly increase along with soil total nitrogen increased,but there are no obvious relationship between plant species diversity,richness and total soil phosphorus,soil moisture content.There are single peak pattern relationship between plant species diversity,richness and available phosphorus content.There is a single peak pattern relationship between Magalef richness index and soil available potassium.(4)The niche width of dominant species ranges from 0 to 2.26 in the swamp wetlands of the Lhasa River Basin.Aster souliei,Kobresia humilis,Triglochin maritima,Carex moorcroftii,Potentilla anserina have the highest niche width in the swamp wetlands that indicate they have strong adaptability to the swamp wetland environment.While the niche width of Hippuris vulgaris,Potamogeton natans,Potentilla saundersiana and Blysmus sinocompressus were zero that indicate their adaptability to the swamp wetland environment is extremely weak.The number of species with a niche overlap value than 0.6 among the 10 marsh wetland plants in the Lhasa River Basin were less,and most of the species of the dominant plant species have a niche overlap value of range between 0 and 0.6.(5)As a whole,the relationship of dominant plant species showed positive interspecies associations insignificantly in the Lhalu Wetland,Maidika Wetland,Naga Wetland,Nailang Wetland and Zhaxigang Wetland.While the relationship of dominant plant species showed negative interspecies associations insignificantly in Are Wetland,Gurong Wetland,Jiagie Wetland,Qucai Wetland and Riduo Wetland as a whole.However,the number of positive interspecies association of the dominant species pairs more than the number of negative interspecies association of them in the Naga wetland.The number of negative interspecies association of the dominant species pairs more than the number of positive interspecies association of the dominant species pairs in the rest of swamp wetlands.There were few numbers of significant positive or negative interspecies associations of the dominant species pairs in the swamp wetlands,Lhasa River Basin.