| The study of the coexistence and diversity maintenance mechanism of community species has always been one of the core research issues of ecology.Through the study of community phylogenetic structure and functional traits,it is possible to quantify the relative roles of deterministic processes(environmental filtering,competitive exclusion,and limiting similarity)and stochastic processes in the process of species coexistence,accurately evaluate decision-making key ecological processes for species coexistence.The alpine meadow plant community plays an irreplaceable role in maintaining biodiversity and ecological balance in high-altitude areas,providing basic scientific data for the coexistence and diversity maintenance mechanism of species in this region.Five different altitude gradients(3000 m,3250 m,3500 m,3750 m,4000 m)were established in the study area.Soil water content SWC,soil temperature ST,soil p H,soil organic carbon SOC,soil total nitrogen STN,soil total phosphorus STP)and plant functional traits(plant height PH,specific leaf area SLA,leaf dry matter content LDNC,leaf organic carbon content LCC,leaf total nitrogen content LNC,leaf total phosphorus content LPC and relative chlorophyll content SPAD)were measured and recorded.Based on DNA barcode data,a high-support and high-resolution phylogenetic tree of alpine meadow plant communities was established,and the species composition,functional trait structure,and phylogenetic structure characteristics of communities at different altitudes were studied.Differences and changing laws,expounding the mechanism of species coexistence in plant communities.This article attempts to explore the main drivers of coexistence of plant species across altitude gradients using a species and community phylogenetic structure combined with functional traits.The results are as follows:(1)With the increase of altitude,soil temperature,water content,soil total nitrogen and organic carbon all showed a decreasing trend.After community statistics,a total of75 herbaceous species were recorded,belonging to 26 families and 54 genera.The dominant families were Compositae(11 species),Gramineae(8 species)and Cyperaceae(3 species).Plants have different distribution characteristics at different altitudes,among them,Gramineae and Cyperaceae with strong stress tolerance are distributed at altitudes of 3000-4000 m.At the same time,Asteraceae plants are widely distributed at 3000-3750 m above sea level.The number of plant families and genera showed a monotonically decreasing trend,while the number of rare species in the community increased monotonically.Based on the sparse curve,it is concluded that as the number of species increases,the Shannon-Weiner diversity index of the community also increases gradually.When the number of individuals exceeds a certain number,the quadrat curve tends to be flat to the right and the community tends to be stable.(2)The community species richness and phylogenetic α diversity PD showed a unimodal variation with the increase of altitude,that is,the plant community species and phylogenetic α diversity reached the maximum at an altitude of 3500 m;SES·PD value and species richness had no significant difference.The correlation of,in the mid-altitude gradient,the SES·PD value is high and positive,and the SES·PD value at an altitude of 4000 m is minimum and negative.The phylogenetic β diversity index showed a gradually increasing trend with increasing altitude,which to a certain extent reflected that species coexistence was significantly affected by habitat filtering.Plant communities in low-altitude(3000 m)and low-middle-altitude(3250 m)areas showed a phylogenetic over-dispersion structure(SES·MPD>0,SES·MNTD>0),which indicated that competitive exclusion was the main driving force for species coexistence;at mid-altitude(3500 m,3750 m),both over-dispersion and clustered existed at the same time.Phylogenetic structure,habitat filtering and competitive exclusion jointly maintained community species diversity;high-altitude(4000 m)community phylogenetic structure clustered(SES·MPD<0,SES·MNTD<0),and the driving factors were related to species convergent evolution and habitat filtering.Soil temperature,soil water content,p H and soil nutrients at different altitudes have different degrees of influence on the plant community phylogenetic structure,among which the influence of soil temperature and water content is extremely significant.(3)The analysis results based on functional traits showed that plant specific leaf area,leaf organic carbon,and total phosphorus showed weak phylogenetic signals,which were affected by a certain degree of phylogenetic history.None of the traits showed phylogenetic signals,indicating that plant functional traits were not greatly affected by species evolution;with the increase of altitude,the functional structure of plant functional traits changed from over-dispersion(NFI < 0)to clustered(NFI > 0)transition.The functional traits of coexisting species exhibit a certain degree of correlation,which reflects the tendency of species to exhibit convergent evolution under the influence of similar environments.The intraspecific variation of the seven traits indicates that the performance of the traits is related to the environmental screening process.After species with similar traits gather together,in order to reduce the intensity of biological competition such as neighbor interactions,individual functional traits will diverge and change..In summary,our study concluded that soil environmental factors,plant functional traits and phylogenetic structure of alpine meadow communities on the Tibetan Plateau all changed with the altitude,and soil temperature and soil water content were the main environmental factors affecting habitat and species coexistence in alpine meadow.Although interspecific competition and habitat filtration are one of the main forces for species coexistence,there are still neutral processes and similarity constraints.It can also be seen that deterministic processes and non-deterministic processes play different roles at different altitudes.And the deterministic process plays a key role in the whole process of species coexistence mechanism of plant community in the alpine meadow study area along the altitude gradient. |
PDF Full Text Request