Study On The Functional Traits Of Fine Roots Of 20 Subtropical Tree Species

Fine root is the organ for plants to absorb nutrients and water from the soil.Because of their fast growth and short life span,fine roots played an important role in forest ecosystem productivity,carbon cycle,and nutrient return.Compared with the above-ground,the underground ecological environment such as soil is more complicated.In order to adapt to the requirements of soil physical resistance,water,nutrient acquisition,etc.,the fine root functional traits are significantly different from those of leaves.Root ecology study has begun in the 1970s.In recent years,based on the fine root order,the anatomical structure,morphology,nutrient content and other traits have been studied.However,integrating the mycorrhizal colonization and phylogeny of fine roots,and analyzing the differences in the fine roots functional traits among different tree species remains to be studied.In this study,three secondary forests with different restoration stages were selected in Dashanchong Forest Park,Changsha County,Hunan Province.The fine roots of 20 main tree species were collected,and their fine roots were distinguished from different order,then determined functional traits of 1 to 3 order fine roots,including morphological indicators,anatomical structure,nutrient content,and degree of mycorrhiza colonization.The functional traits were analyzed by variance analysis,principal component analysis,Pearson correlation and phylogenetic independent comparison.The mainly aims of this study were:(a)By comparing the index parameters of different root sequences of different mycorrhizal tree species,analyzing the interspecies variation of their traits.(b)Studying the relationship between mycorrhizal fungi and species nutrient absorption strategies Relationship.(c)Study the relationship between the functional traits of 20 representative tree species and their phylogeny.The main results are as follows:(1)Tree species and root order have significant effects on the functional traits of roots.With the increase of root order,root C content,root diameter,root tissue density,cortex thickness and stele diameter increased significantly,while root N content,specific root length,root specific surface area and mycorrhizal colonization rate decreased significantly.The species are divided into EM tree species and AM tree species according to the types of mycorrhizal infecting fungi.The root C content,average diameter,average specific root length,average root specific surface area and root bark thickness of the fine roots of EM tree species are lower than AM tree species.The root N content of the two is similar,and the root tissue density and the column diameter of the fine roots of the EM tree species are higher than that of the AM tree species.(2)There was no correlation between the stele diameter and the mycorrhizal colonization rate of ectomycorrhiza(EM)and arbuscular mycorrhizas(AM)tree species.The mycorrhizal colonization rate of AM tree species is significantly positively correlated with root N concentration,root diameter,and cortex thickness,and significantly negatively correlated with root C content,C/N ratio,specific root length,specific surface area,and root tissue density Relationship:The mycorrhizal colonization rate of EM tree species has a significant positive correlation with the specific surface area,and a significant negative correlation with the root tissue density.(3)Phylogeny has an impact on root functional traits.There is almost no significant correlation between chemical traits and morphological traits,but is significantly related to anatomical traits and mycorrhizal colonization;morphological traits and anatomical traits are extremely significantly correlated,but not related to mycorrhizal colonization.The correlation between many traits is significantly weakened or even disappeared after removing phylogenetic signals.There is no significant correlation between root N content and diameter,specific root length and cortex thickness,which are traits of resource acquisition strategies.The diameter or thickness of the cortex showed stronger phylogenetic signals in the first order roots than in the 1-3 order roots,indicating that this kind of traits are restricted by the phylogeny,and the phylogenetic signals of other traits are not significant.(4)The results of principal component analysis of functional traits show that there are three main dimensions.The first dimension mainly distributes the traits of resource acquisition-conservation strategy,such as specific root length,specific surface area,cortex thickness,mycorrhizal colonization rate.The second dimension is the distribution of diameter and root tissue density,and nutrients are in the third dimension.