| In this paper,the change of species diversity distribution pattern with slope direction and the effect of common species and rare species on maintaining species diversity in alpine meadow community were studied on the south slope to north.Five models,including logarithm series,geometry series and broken stick model,were used to fit the species diversity models of all species,common species and rare species in the alpine meadow experimental plots in Gannan cooperation area from south slope to north.The change of species diversity distribution pattern with slope direction was analyzed by rad fitting method,and the relative contribution of common species and rare species in different slope direction to species diversity was studied.Combined with the previous research theory,through multiple comparative analysis,linear regression and multiple fitting methods,the species diversity distribution pattern and diversity of alpine meadow were analyzed.The results are as follows:(1)In the south slope to the north slope,the difference of environmental factors is obvious,among them,soil total phosphorus(from 0.5g/kg to 0.7g/kg),organic carbon(from 39.5g/kg to 54.9 g/kg),available P(from 1.294mg/kg to 1.385mg/kg),C / N ratio(from 6.71 to 9.83)and water content(from 15.21% to 35.79%)showed an increasing trend;soil N / P ratio and pH(from 8.1 to 7.0)showed a decreasing trend;total N in the west slope(4.8g/kg)was significantly lower than other slope directions,but the difference of available N in the whole slope direction was not significant;(2)The diversity of the four groups is ranked as formation I(Potentilla fruticose+Kobresia humilis+ Polygonum viviparum+Viola pseudo-bambusetorum)> formation II(Leontopodium leontopodioides+ Kobresia humilis + Thalictrum aquilegifolium)>formation III(Kobresia humilis+ Leontopodium leontopodioides)>formation IV(Kobresia humilis+Aristida adscensionis).Simpson index,Shannon index and richness index are opposite to each other.Formation 1 has the largest Simpson index,indicating that this group is more dominant than the other three formations.The species uniformity index can measure the distribution of species.The higher the uniformity,the more uniform thedistribution of species.The overall diversity of the community is determined by the number of species in the community and their distribution;the Margalef index and Pielou index of formation 1 are the largest,Therefore,the distribution of this group is relatively uniform.(3)On the slope gradient of the south slope,the species diversity of rare species increased significantly,and the corresponding slope species diversity index(Simpson,Pielou,Margalef and Shannon index)increased gradually.The effect of rare species on the community species diversity increased in the south north slope gradient,but the effect of rare species removal in each slope direction was higher than that of common species removal,so the relative contribution of rare species to the species diversity of alpine meadow in Gannan was higher than that of common species;(4)The slope of species abundance distribution curve decreased from south slope to north slope.With the change of slope from south to north,species diversity and species diversity are increasing.Six models were used to fit the species diversity distribution of slope gradient.It was found that the niche model was the main species diversity distribution model,followed by the random distribution model.On the whole,the distribution pattern of species on the microhabitat gradient of the alpine meadow in the Qinghai Tibet Plateau is mainly fixed.(5)Random fraction model is the main mode of rare species resource acquisition in each slope direction,while geometric series model is the main mode of common species.Due to the large diffusion rate of rare species,the niche overlap between species will be more obvious in the ecosystem with high species diversity,so as to inhibit the increase of species diversity,so as to maintain the original species diversity. |
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