Functional Niches And Their Geographic Differentiations For Woody Plants In Four Forest Vegetation Types Across Different Climatic Zones In China

Niche is the spatial/temporal position and role of a species in an ecosystem,which is actually the sum of all living conditions of the species.Plant functional traits are the attrabuties of a species best fit for survival,during their long term interactions with the environmental conditions.Because it is difficult to completely obtain the habitat gradient parameters of plants,it is almost impossible to study niche strictly according to the its theoretical definition.Therefore,the niche analysis is conducted mostly by indirect methods.In recent years,construction of multi-dimensional functional niche based functional trait is a new approach to elucidate plant adaptability and its potential distribution.Functional niche is the relative position of species in the multidimensional functional space.Similar to the periodic table of elements in chemistry,the periodic table of niches for species is defined as the niche relationships and their order tables in a biotic community.Because of the multi-dimensional spatial property of niche,we can’t understand the niche periodic table by using the same model of two-dimensional element periodic table.Analysing functional niches and their periodicities for plants in forest vegetation types across different climatic zones is highly significant in the theoretical explorations for community assembly,successional dynamics and geographic differentiations of different forest vegetation types.In this study,woody plants in four forest vegetation types across different climatic zones in China were taken as the research object.Based on the investigation of already established forest dynamics plots [From April 2018 to July 2019,fifty 20 m × 20 m forest dynamic plots were separately established in Tropical rainforest(Bawangling,Hainan),Subtropical evergreen-deciduous broadleaved mixed forest(Mulinzi and Xingdoushan,Hubei),Temperate coniferous-broadleaved mixed forest(Xiaolongshan,Gansu),and Cold-temperate coniferous forest(Kanas,Xinjiang)],as well as measuring functional traits of woody plants and environmental factors,and combined with information gathering from online available common databases,this thesis explored the functional niches based on functional traits and niche periodicities of woody plants in forest vegetation types across different climatic zones,and identified the dominant functional dimension of functional niches.The key abiotic(climate,soil)and biotic(community structure,phylogenetic characteristics)factors which influenced the geographic differentiations of functional niche hypervolumes of woody plants in different forest vegetation types were examined in order to further develop the theory of functional biogeography,and provide a scientific basis for the conservation and restoration of forest vegetation across different climate zones in China.The main results are as follows:(1)In the functional niche spaces of woody plants in the four vegetation types,leaf economy was the dominant functional dimension,followed by mechanical support and reproductive phenology.In the dimension of leaf economy,specific leaf area was the main functional gradient in Tropical rainforest,Subtropical evergreen-deciduous broadleaved mixed forest and Cold-temperate coniferous forest,while leaf dry-matter content was more important in Temperate coniferous-broadleaved mixed forest.In the dimension of mechanical support,the main functional gradient for each forest vegetation type was stem tissue density,except in Cold-temperate coniferous forest,which was plant size.In Tropical,Subtropical and Temperate forests,distant related species of different families with similar functional trait combinations repeatedly appeared in the similar functional niche spaces,indicating that functional niches of woody plants have periodicities.(2)The functional niches of woody plants in forest vegetation types across different climatic zones had siginificant geographical differentiations.With the increase of latitude(from Tropical rainforest to Cold-temperate coniferous forest),plant specific leaf area increased,stem tissue density decreased,leaf area and plant size decreased,reflecting the transformation of resource use strategy of woody plants from conservative to acquisitive.Functional niche spaces for woody plants of different forest vegetation types(Tropical,Subtropical,Temperate,Cold-temperate forests)generally diverged,albeit some woody plants’ functional niches in Subtropical forest converged with those of the Tropical and Temperate forests.(3)The hypervolumes and their overlaps of functional niches for woody plants in forest vegetation types across different climatic zones showed apparent geographical differentiation patterns.The functional niche hypervolumes of woody plants decreased from Tropical rainforest to Cold-temperate coniferous forest.The overlap degrees of functional niche hypervolumes of woody plants in different forest vegetation types decreased gradually with the increase of latitude spans,suggesting that the functional differences of woody plants in different vegetation types increased with the latitude spans.The overlap degree of functional niche hypervolumes was the highest between Subtropical forest and Temperate forest(Overlap index=0.67),while the overlap was the lowest between Tropical forest and Cold-temperate forest(Overlap index=0.19).(4)The total explanatory power of climate and soil on the differentiations of functional niche hypervolumes of woody plants in forest vegetation types across different climatic zones was50%,in which,the explanatory power of climate(28%)was higher than that of soil(16%).The functional niche hypervolumes were positively correlated with annual mean temperature and annual precipitation,and negatively correlated with soil p H value,organic matter content,total nitrogen and phosphorus contents.Annual mean temperature,soil p H value,and soil total nitrogen were the key environmental factors that affected the geographic differentiations of functional niche hypervolumes of woody plants in different forest vegetation types.(5)Among the four community structure indexes(species richness,species abundance,potential maximum plant height and DBH area),only species richness had a significant effect on the geographic differentiations of functional niche hypervolumes of woody plants in forest vegetation types across different climatic zones.The functional niche hypervolumes and species richness had a positive correlation.(6)The functional niche hypervolumes of woody plants in forest vegetation types across different climatic zones showed a unimodal change pattern with the community phylogenetic distances(MNTD and MPD).The functional niche hypervolumes increased gradually in the Tropical,Subtropical and Temperate forest,while it decreased in the Cold-temperate forest.