Functional Traits Of The First-order Roots Of 89 Woody Species In A Mid-subtropical Evergreen Broadleaved Forest

As a bridge between plants and the external environment,plant functional traits have become a hot field in modern ecological research.However,researches on the functional traits of plants are mainly focused on the aboveground organs,and the functional traits of underground organs,for example,fine roots,received much less attention.This study took Wanmulin Nature Reserve as the research site,selected 89 woody species in a mid-subtropical evergreen broadleaved forest and measured the morphological and stoichiometric traits of the 1-order fine roots through field sampling and indoor analysis.The purpose of this study is to illustrate the general trends in the inter-specific variations of 1st-order root traits of woody species in a mid-subtropical evergreen broadleaved forest,to clarify the existence of "root economic spectrum" in this forest,and to explore whether functional traits of fine roots are affected by phylogenetic history.It provides theoretical basis for the accurate prediction of forest dynamics,community species diversity and ecosystem function changes under the background of global climate change,and also provides basic data for the establishment of global fine root ecological model.The results are as follows:(1)Based on the analysis and comparison of the basic data of inter-specific variation of 1st-order root functional traits,this study was found that the morphological and chemical traits of the fine roots were different from each other.In particular,there are huge variations in the diameter of fine roots.so the "diameter method" has great defects in the division and definition of fine roots,and the "root order method" is more scientific in the study of fine roots.(2)By comparing the differences of 1st-order root functional traits in different leaf habits and growth types,it was found that the root carbon concentration of evergreen woody species was significantly higher than that of deciduous woody species(P<0.05).The root diameter and root length of arbor were significantly larger than those of shrubs(P<0.05).The specific root length of shrubs was significantly larger than those of arbor.Comparing the differences of 1st-order root functional traits in different life form,it canbe found that the root diameter of deciduous arbor,evergreen arbor,evergreen shrub/semi-tree were significantly higher than that of evergreen shrubs(P<0.05).The specific root length of evergreen shrubs was significantly higher than that of evergreen arbor,deciduous arbor,evergreen shrub/semi-tree(P<0.05).The carbon concentration of evergreen shrubs was significantly higher than that of deciduous arbors and deciduous shrubs,and the carbon concentration of deciduous arbor was significantly higher than that of deciduous shrubs(P<0.05).The nitrogen concentration of deciduous arbor was significantly higher than that of evergreen shrubs(P<0.05).(3)By comparing the correlation analysis of the first-order root functional traits,it was found that the root diameter was negatively correlated with root tissue density and positively correlated with root nitrogen concentration.There was no correlation between specific root length and root nitrogen concentration.These showed that the correlation between root morphology and root chemical traits was inconsistent with the expected result of "root economic spectrum".It may be that the mycorrhizal symbiosis counteracts the natural selection of root economic spectrum,or it may also be that the root trait itself has multidimensional variation.(4)Through principal component analysis of the 1st-order root main functional traits,it was found that there were two principal components and both of them were important.The first principal component is dominated by the specific root length.Including diameter,average root length.It represents the law of diminishing returns to root length investment.The second principal component contains diameter,root tissue density and root nitrogen concentration,and those of which are related to physiological metabolic indexes such as respiration rate and life span of fine roots,reflecting the trade-off between root resource acquisition and resource conservation strategies.This also shows that the root traits variation is not one-dimensional,but is affected by a combination of multiple biophysical mechanisms,showing a multi-dimensional pattern.In addition,root diameter plays a prominent role in both principal components,indicating that diameter may play multiple roles.(5)Phylogenetic studies on the 1st-order root traits showed that root tissue density and nitrogen concentration of 1st-order root had significant phylogenetic signals(P<0.05),while other traits were not affected by phylogenetic background(P>0.05).Phylogenetic independence analysis(PIC)was used to compare the correlations among traits.It was found that the correlation disappeared between root diameter and root length,root nitrogen concentration and root C:N.The correlation between specific root length and root carbon concentration disappeared.The correlation between root tissue density and root nitrogen concentration and root C:N disappeared.The specific root area is independent of root carbon concentration.It may indicate that the covariation of morphological and chemical traits were mainly determined by phylogeny.In summary,there are two-dimensional variations of the 1st-order traits of woody plants in the mid-subtropical evergreen broad-leaved forest in Wanmulin Nature Reserve.And we found that there is no “root economic spectrum”.Some functional traits of1st-order root were affected from the life form(including leaf habits and growth type)and phylogenetic background.