Variation Of Plant Functional Traits And Maintenance Of Diversity In Temperate Forests

Explaining the assembly and maintainance of biodiversity patterns is one of central questions in ecology.In recent years,plant functional traits are increasingly used to describe biodiversity patterns and their underlying mechansims.Functional traits can be covaried or decoupled with each other and show influences on plant growth and survival,which will enventually influence commnity structure,composition and diversity.Here we used root and leaf traits to explore how functional traits vary,are correlated,influence plant demographic rates,biotic interactions and community diversity.(1)We measured lamina and petiole traits for more than 2800 seedlings in 283 seedling plots to quantify trait variation and correlation.We found about 40%variation in leaf-level traits was explained by ITV across all traits.Lamina and petiole traits were correlated,whereas leaf size traits were weakly correlated with economics traits;lamina mass ratio was strongly related to the petiole length.There was no evidence that the strength of trait relationships was stronger at broader than finer biological and spatial scales.Increasing trait variance and decreasing sample size will increase the strength of trait correlations.Our results showed that a large amount of trait variation was explained by ITV,which highlighted the importance of considering ITV when using trait-based approaches in seedling ecology.In addition,comparing trait correlations across studies should consider the differences in sample size.(2)While leaves were larger for higher seedlings,leaf economics spectrum traits were more conservative with increased height and at high light and low elevation conditions.Increased height could improve seedling survival directly,and by increasing their leaf area indirectly.Meanwhile,increased height could impede seedling growth directly,but improve growth indirectly by increasing leaf size and showing more conservative trait values.Environments did not influence seedling survival and growth directly but could influence growth indirectly by mediating trait variation.Finally,height-driven variation in leaf area could explain the height-driven variation in survival across species,meanwhile,height-driven variation in leaf chlorophyll content could explain height-driven variation in growth among speeies.Our study suggests that functional traits are important intermediary agents to mediate the seedling demographic rates in changing ontogenies and environments and explain the species-specific response to these gradients.(3)We used a global database to explore how fine root traits differed between AM and EM woody species.We found that diameter-related root traits showed the strongest differences where AM plant species thicker cortex,larger root diameter and lower tissue density,compared to EM plant species.We did not find significant difference in specific root length between AM and EM plants.The nutrient-related root traits exhibited weak trait differences where AM plant species showed nutrient acquisitive strategies with higher nitrogen and phosphorus concentrations and carbon to nitrogen ratio than EM plant species.The AM-EM trait differences were slightly more pronounced for co-occurred species at the site-level and first order and absorptive roots.Our study provides evidence that the fine roots of AM plants tend to be thicker and show the resource acquisitive strategies and fine roots of EM plants be thinner and show the resource conservative strategies.(4)Using seedling and sapling survival in broadleaved Korean-pine and valley spruce-fir forest plots in Northeast China,we evaluated the effects of both conspecific and heterospecific neighbour density,as well as the soil and light environments,on the survival of AM and EM-dependent trees.While light availability increased the survival of EM seedlings,soil organic resources increased EM sapling survival in the spruce-fir plot.AM tree species suffered stronger CNDD than did EM tree species in both plots.In the spruce-fir plot,soil factors and light availability mediated species CNDD but their effects differed between AM and EM species,and also between seedlings and saplings.For seedlings in both plots,we found that AM species exhibited a positive relationship between species abundance and CNDD strength,whereas this relationship was negative for EM species.Our results suggest that plant mycorrhizal type can mediate species responses to intra-and interspecific interactions and the direct effects of local environmental conditions on seedling and sapling survival.(5)We assessed 305 species across 15 large,stem-mapped temperate forest dynamics plots in Northeastern China and North America to explore the relationships between tree mycorrhizal type and CNDD,species abundance,and species richness at a regional scale.AM tree species showed a stronger CNDD and a more positive relationship with species abundance than EM tree species.For each plot,both basal area and stem abundance of AM tree species was lower than that of EM tree species.Finally,EM tree dominance showed a negative effect on plant richness across plots.These results indicate that the results in research(4)can be generalized in regional scale,and mycorrhizal type can further influence community structure and diversity.