Altitude Effect Of Species Abundance Distribution Pattern Of Plant Community In Alpine Meadow Of Gannan,China

The study of species abundance distribution pattern is of great significance for the understanding of community structure,which can reveal the distribution mechanism of biodiversity and provide help for the effective protection of biodiversity.The alpine meadow on the Qinghai-Tibet Plateau contains huge biodiversity,which plays an irreplaceable role in the protection of the global ecosystem.In order to analyze the characteristics of the species abundance distribution pattern of the plant community with the altitude gradient,to explore the formation law and maintenance mechanism of species diversity,this paper takes the Gannan alpine meadow plant community in the northeast of Qinghai-Tibet Plateau as the research object.On the gradient of different elevations(3000,3250,3500,3750 and 4000 m),the typical sample plot survey method was used to collect data and information,and the vertical distribution characteristics of plant communities in alpine meadows were discussed based on the relevant theories and methods of quantitative ecology.Niche overlap model,lognormal distribution model,geometric series model,broken stick model and random distribution model were selected to study the changes of species abundance distribution of alpine meadow plant communities at different elevations.The results show that:(1)With the increase of altitude,all kinds of environmental factors have changed significantly.Soil temperature,soil total nitrogen,soil total phosphorus and soil conductivity showed a gradual downward trend;soil water content increased at first and then decreased;light intensity,soil organic carbon and soil nitrogen-phosphorus ratio showed a gradual increasing trend;soil p H value decreased at first and then increased gradually;soil carbon-nitrogen ratio increased obviously with the increase of altitude.(2)The plant communities in the study area were divided into 5 types by multiple regression trees: AssociationⅠ: Potentilla fruticosa-Kobresia humilis;AssociationⅡ:Potentilla fruticosa-Kobresia humilis + Leontopodium nanum;Association Ⅲ :Kobresia humilis + Anemone trullifolia-Potentilla fruticosa;AssociationⅣ: Kobresia Willd + Kobresia humilis + Gentiana macrophylla;AssociationⅤ: Kobresia Willd +Polygonum macrophyllum.(3)With the change of altitude from 3000 m to 4000 m,the species diversity of plant community changed obviously,the species diversity was in the order of altitude >low altitude > high altitude,and the species diversity of middle altitude community was the highest,that is,the "intermediate expansion" model appeared.With the increase of altitude,the change of the number of common species is very small,while the number of rare species increases at first and then decreases,and the number of rare species is higher than that of common species,but the diversity index of common species is obviously larger than that of rare species.Therefore,it is said that the main contributor to the species diversity of the community is the common species.(4)With the increase of altitude,the slope of the relative abundance curve of all species decreased at first and then increased.The species distribution was the most uniform and the species richness was the highest at 3500 m,while it was just the opposite at 4000 m.The fitting effects of the five models on the abundance distribution of all species at different elevations are different,among which the geometric series model is the best at all elevations,so it can be inferred that birth niche differentiation plays a leading role in the construction of plant communities in alpine meadows.The best fitting model of common species abundance distribution is geometric series model,which is consistent with the optimal model of all species abundance distribution,indicating that common species are the main reasons that affect the species abundance distribution of the community,and the resource allocation model is mainly fixed allocation.The abundance distribution of rare species is relatively consistent with the ecological process represented by random assignment model,and its resource allocation model tends to random allocation.Common species should be regarded as priority protected species,but at the same time,the special role of rare species in the community should not be ignored,they jointly maintain the species diversity of alpine meadows on the Qinghai-Tibet Plateau in different ways.(5)At different elevations,all kinds of environmental factors have different effects on species abundance and diversity,among which soil temperature and soil water content are the key factors affecting the species diversity of Gannan alpine meadow plant community.