| Plant diversity is of great significance for understanding the community assembly of vegetation and the geographical differentiation of ecosystem functions among different regions.At present,research on plant diversity is mainly based on vegetation in the same region,but the geographical differentiation pattern and its driving factors of plant diversity across different climatic regions are still lack of in-depth analysis.The factors affecting plant diversity between different regions include abiotic factors such as climate,soil,and biotic ones e.g.competition,neighbor size and individual density.Therefore,the two types of factors and their interactions must be taken into account in the analysis of biodiversity patterns and maintenance mechanisms.In recent years,integrating biotic and abiotic factors as a "compound habitat" or “integrated habitat” to analyze the spatial and temporal pattern of biodiversity has become a new attempt in biodiversity research.Based on woody plants in different forest vegetation in four climatic regions(tropical,subtropical,temperate,cold temperate),the ecological gradient axis was constructed based on community survey/monitoring and measurements for environmental factors and plant functional traits.This thesis analyzed the differentiation pattern and driving factors of forest plant diversity(including species diversity,functional diversity and phylogenetic diversity)with the integrated habitat gradient,explored the relative role of environmental filtering,biotic competition,random process and regional species pool in the assembly of forest communities in different regions,elucidated the underlying factors driving t geographical differentiation forest vegetation across different climatic zones,and providing a scientific basis for the conservation of forest biodiversity in China.The results were as follows:(1)Based on the biotic and abiotic factors such as climatic characteristics,community structure and soil nutrients of forest dynamic plots in different regions,the integrated habitat gradient axis was constructed by principal component analysis(PCA)method.The first four axes of the PCA explained 74.8% of the total variation for all the 15 variables.The first axis(PC1)accounted for 32.6% of the variation,the dominant factors were temperature,rainfall,and average DBH of community trees,representing the trend of integrated habitat gradient variation from low temperature,less moisture and simple community structure to high temperature and rainy,complex community structure.And the second axis(PC2)accounted for 22.5% of the variation,the dominant factors were crown height of forest and soil nutrients,representing the trend of integrated habitat gradient variation from fertile soil,high forest canopy layer to barren soil,lower forest canopy layer.(2)The species diversity of forest vegetation was positively correlated with the PC1 axis,i.e.all the species diversity indexes increased gradually with the increase of the PC1 axis.Which Shannon-Wiener index and Simpson index decrease significantly with the PC2 axis.Climate and biotic factors significantly influence the species diversity of forest vegetation in the cross-climate region of China.(3)The weighted mean and variance of community level specific leaf area and leaf phosphorus content decreased significantly with the increase of the integrated habitat gradient PC1 axis;the community weighted mean and variance of leaf dry matter content,leaf slice nitrogen-phosphorus ratio and wood density increased significantly with the increase of the PC1axis;however,the community weighted mean and variance of leaf nitrogen content did not show significant regular changes with the PC1 axis.At the community level,the weighted skewness and kurtosis of the six functional traits increased significantly with the increase of the PC1 axis,and the weighted skewness of each trait tended to zero,while the weighted kurtosis of each trait was far away from zero.The change trend of weighted mean,variance,skewness and kurtosis of each functional trait on PC2 axis was different from that on PC1 axis,and the correlation with PC2 was weak.Most of the community weighted mean,variance,kurtosis and skewness of each functional trait had significant correlations.The differences in the composition of functional traits among forest communities in different climatic regions were due to the convergence of traits caused by the environment,as well as the competition among species processes responding to local scale filtration in the communities,the environment constructs community composition by selecting the optimal traits.(4)The functional diversity index of the forest vegetation all increased significantly with the increase of the PC1 axis of the integrated habitat gradient.Functional dispersion and Rao Q index increased with the increase of the PC2 axis,while the functional richness and functional evenness decreased with the increase of the PC2 axis.There was a significantly positive correlation between functional richness(FRic),functional evenness(FEve)and Rao’s quadratic entropy index(Rao Q)and species diversity,while there was no significant correlation between functional dispersion(FDis)and species diversity.In species-rich communities,with the increase of functional diversity,the variation of traits may be higher.(5)The phylogenetic diversity index of forest vegetation PD increased significantly with the increase of PC1 axis,and no significant regularity change with the PC2 axis.While the MPD and MNTD decreased significantly with the increase of PC1 axis,but increased significantly with the increase of PC2 axis.The correlation between phylogenetic diversity and species diversity was significant,but the correlation between functional diversity and species diversity was weak.Environmental filtering and interactions between organisms may be responsible for the coexistence of different consanguineous species in plant communities.Phylogenetic diversity were influenced not only by the relationship among species,but also by the number of species and functional traits.(6)The phylogenetic conservatism of functional traits for the forest vegetation was not strong,which was lower than the expected value of Brown model.Among them,four functional traits(specific leaf area,leaf dry matter content,leaf phosphorus content and wood density)showed significant phylogenetic signals,while neither leaf phosphorus content nor leaf nitrogenphosphorus ratio showed significant phylogenetic signals.The phylogenetic diversity structure and functional diversity structure of forest vegetation changed from aggregation to divergence with the integrated habitat gradient PC1 axis,suggesting that competitive exclusion dominated community assembly in the tropical and subtropical forests,while environmental filtering played a key role in the cold temperate forests.The interaction of habitat filtering and biotic-competition exists in the process of community construction of cross-climatic forest vegetation in China.Our results showed that the vegetation diversity indexes were significantly related to the composite habitat gradient PC1 axis,the environment and interspecies competition leads to the difference of plant functional traits in communities,reviewed the research progress and relevant theoretical hypothesis of forest ecology,and studyed the plant diversity distribution pattern and construction mechanism on a large scale,which was of great theoretical significance for understanding the geographical differentiation rule of different regional ecosystems. |
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