Functional Responses Of Forest Woody Plants To Environmental Gradients In Ningbo Region,Zhejiang Province

Plant functional traits have long been recognized for the mechanistic quantification of species diversity.However,our understanding about the patterns of variations in plant functional traits for determining community assembly at different ecological scales remains poorly known.In this thesis,six functional traits including mean leaf area,specific leaf area,leaf dry matter content,leaf nitrogen content,leaf phosphorus content and twig wood density of woody plants were measured across 94 plots in evergreen broadleaf forests of Ningbo region of Eastern China.Soil physicochemical properties including soil moisture content,bulk density,total carbon content,total nitrogen content and total phosphorus content,and topographic factors were measured to represent environmental factors of the studied plots.First,the variances of six functional traits on four nested ecological scales(region,community,species and individual)were decomposed using a linear mixed model.Second,the RLQ analysis and Fourth-corner method were used to establish functional traits-species abundance-environmental factors matrix in order to analyze variations in plat traits along environmental gradients.Finally,the responses of functional trait diversity and composition to environmental factors were analyzed at the community scale by RDA analysis.The main results of this thesis showed that:1.The variability of six plant functional traits showed different patterns at four ecological scales.The variability in leaf morphological traits were strongly observed at species and individual scales whereas very weakly observed at regional scale.The leaf chemical traits and twig wood density showed different degrees of variations at individual,species and community scales,but their variation distributions at different ecological scales were more uniform than those of leaf morphological traits.The variations of these six functional traits at regional scale were generally low,indicating that the responses of plant functional traits to environmental changes were mainly dependent on species and community scales in the studied forests.2.When considered the mean values of plant functional traits,the results showed that species with larger leaf area are strongly located on nutrient-rich soils(i.e.high soil total nitrogen and phosphorus contents).On the contrary,species with high leaf nitrogen content are located on nutrient-poor soils(i.e.low soil total nitrogen content).When considered the coefficient of variation of plant functional traits,results showed that altitude is negatively correlated with functional traits except leaf phosphorus content,indicates that high variability in traits is located on low altitude.High variation in leaf area,specific leaf area,leaf dry matter content and twig wood density are located on soils having high bulk density.Besides,in the habitats with low soil moisture content,species which have high variations of leaf area,twig wood density and leaf nitrogen content were more abundant.Species with high variation in leaf dry matter content were highly abundant on nutrient-rich soils,but species with high variations in twig wood density and leaf phosphorus content were highly abundant on carbon-poor soils.In combination,the results suggest that coefficient of variation rather than mean of functional traits are strongly related with environmental factors in the studied forests.Therefore,I concluded that effects of environmental filtering on community composition are mainly due to the environmental plasticity of plant functional traits rather than the inherent traits of species.3.The community-weighted mean(CWM)of different traits had different responses to environmental factors.Species with large mean leaf area and specific leaf area are dominated in the communities with high soil nutrients and moisture content.The positive correlations of CWM of leaf chemical traits with soil bulk density and elevation,indicating that communities having high leaf nitrogen and phosphorus contents are located on compact soils of high altitude.The CWM of leaf dry matter content and twig wood density were negatively correlated with soil moisture content,indicating that communities by dominated species having low twig wood density and leaf dry matter content are located on soils with high moisture content.4.Soil bulk density was negatively correlated with RAO’s quadratic entropy index of six functional traits,which indicates that niche differentiation occurred on less compact soils.The RAO’s quadratic entropy index of mean leaf area,leaf dry matter content and phosphorus content were positively correlated with soil moisture content and elevation,and that of specific leaf area,twig wood density and leaf nitrogen content were positively correlated with soil total nitrogen and total phosphorus contents,indicating that niche differentiation occurred on nutrient-rich soils.In conclusion,this thesis revealed the effects of environmental filtering on community assembly and the distributions of woody plants along environmental gradients at different ecological scales in the studied subtropical forests.The research showed in this thesis provides sufficient evidences for species diversity and community assembly at different ecological scales in Ningbo region of Eastern China.