The Pattern Of Species Richness And Main Functional Traits Of Seed Plants Along An Elevational Gradient In Qinling Mountains

Diversity patterns along altitudinal gradients and underlying mechanisms had been important topics in the field of ecology.However,the patterns of species richness at large scale and explanatory ability of various hypotheses still be worth revisiting.Basing on the distribution data of 3538 species along altitudinal gradient derived from local flora of entire Qinling Mountains,we analyzed the patterns of endemic species and species richness,tested the explanatory ability of different hypotheses,and the applicability of the Rapoport's rule in this region.In addition,many plant traits,which were easy to observe and measure,could objectively reflect responses to changing temperature regimes and other factors along elevational gradients.There was little research on the relationship between altitudinal gradient and plant traits of a large number of species in a region,and more data testing and mechanism researching were need for the complexity of influencing factors.The results were as follow:Total species richness showed a unimodal pattern along the altitudinal gradient,and the richness of three taxonomic families,genera and species showed a similar trend,while endemic species richness had significant monotonic increasing with elevation.Then,we compared the explanatory ability of species-area relationship(SAR),metabolic theory of ecology(MTE)and mid-domain effect hypothesis(MDE).The independent interpretation of the three hypotheses was very small,but the joint interpretation of SAR and MDE was large(80.4%).The result of Pagel upper method supported the Rapoport's rule,but the results of Cross-species method,Rohde's mid-point method and Stevens method didn't support the Rapoport's rule,but after the tests by sectioning method,the linear trend was more obvious.There were abundant life forms in Qinling Mountains.In high altitude areas,the hemicryptophyte and geophyte were dominant.The leaf length,width andlength-width ratio decreased monotonously with altitude,and the number of microphyll was the largest.Whose shapes changed less than the others,the leaf area of Phanerophyte gradually decreased with altitude.The average seed quality decreased with altitude,but it fluctuated at low altitude.The results of seed quality grading showed that 1000-seed mass below 1 g had better adaptability at high altitude and were consistent with the wind-borne species increasing with altitude.Compared the seed weight of different life-form,the seed quality of Phanerophyte was the highest,which supported the seed quality was related to plant size.The results showed that the unimodal pattern of species richness was the result of the concerted action of manifold factors.Single hypothesis could not fully explain the pattern of species richness along altitude gradient in Qinling,but area and geometric constraint were the major factors.However,the test results of applicability of the Rapoport's rule were obviously influenced by the analytical methods,and the influence of mid-domain effect could be partially eliminated by grouping species according to their distribution range,then the results were more support the Rapoport's rule.The leaf areas decreased with the elevation,which accorded with the rule that small leaf plants were more suitable for cold regions.The seed quality was related to the plant size,and small seeds were restricted by resource factors at high altitude.