Coordination Patterns Of Interspecific Variation Between Leaf And Root Functional Traits In A Subtropical Evergreen Broad-leaved Forest

Plants play a key role in ecosystem processes by adjusting their ecophysiological traits in resource competition in various environments.Studies have found general laws in global based on the above-ground,including "leaf economic spectrum" and "wood economic spectrum".However,the under-ground studies are much less than those,and no consistent laws similar to leaf traits had been found.In recent years,there were many studies for leaf and root functional traits correlation,but most of the studies were carried out on a large scale(mostly in regional or global),and it is unclear whether this large-scale leaf and root functional correlation is also suitable for small-scale(local).This study selected 117 woody plants in a natural subtropical evergreen broad-leaved forest community.Leaf and root were sampled in plant growth season.We measured the morphological traits and chemical traits of leaf and root: leaf thickness(LT),leaf area(LA),leaf tissue density(LTD),specific leaf area(SLA),root diameter(RD),root length(RL),specific root area(SRA),specific root length(SRL),root tissue density(RTD),leaf carbon concentration(LC),leaf nitrogen concentration(LN),root carbon concentration(RC)and root nitrogen concentration(RN).Then measured and analyzed those traits in order to reveal the coordination patterns of interspecific variation in leaf and root functional traits of subtropical evergreen broad-leaved trees,and to understand the resource economic strategies of woody plants in functional traits.The results showed that:(1)The variation range of six leaf functional traits in woody plants in subtropical evergreen broad-leaved forest was 7.8%～82.7%,and the variation degree of morphological traits(35.1%～82.7%)was higher than that of chemical traits(7.8%～28.3%).There were significant differences in leaf habits on functional traits,and the LA,SLA and LN of evergreen species were significantly lower than those of deciduous species,LC were significantly higher than those of deciduous species(P < 0.05).Principal component analysis showed that,there was at least one ecological axis of leaf traits in woody plants related to resource acquisition and conservation in subtropical evergreen broad-leaved forests.Phylogenetic conservatism of leaf chemical traits(LC,LN)was stronger than morphological traits.(2)Root functional traits of woody plants in subtropical evergreen broad-leaved forest showed a certain regularity.First-order roots has the smallest values of RD,RL,RTD and RC,and the largest values of SRL,SRA and RN.From 1 to 5 order root,RD,RL and RTD increased with the increase of root order,while SRL,SRA and RN decreased.The variation range of morphological traits(18.6%～70.8%)was greater than that of chemical traits(3.8%～54.7%).Species were the most important factor in the variation of root functional traits in 1～5 order root.The "root economic spectrum" of woody plants in subtropical regions is multidimensional,with the first principal component(associated with SRA and SRL)representing the carbon investment-return of plant roots,while the second and third principal components are associated with RD and RC,respectively,independent of all other root functional traits.In the subtropical evergreen broad-leaved forest community,the morphological traits of roots from 1 to 5order were less affected by the phylogeny.But the chemical traits were all affected by the phylogeny,and the phylogenetic signal was significant(P < 0.05).(3)There was a strong co-variation between leaf and root functional traits in woody plants in subtropical evergreen broad-leaved forest.The correlation between LN and RN was significantly positive(P < 0.01),indicating that LN could be used to predict underground RN.There were significant positive correlations between LT and RC,LA and RN,SLA and RN,LN and RD,and significant negative correlations between LT and RN,SLA and RC(P < 0.05),but no correlation between other traits.The influence of phylogenetic structure on underground traits was stronger than that on above-ground traits.The influence on chemical traits was stronger than that on morphological traits.The correlation between leaf and root functional traits was enhanced(LC-RC,SLA-SRL,LA-RL).The p PCA showed that,the first principal component was related to resource acquisitive and conservative strategies of leaf and root.The second principal component was related to RD,RTD and LN,independent of other traits.In conclusion,there was a trade-off axis consistent with the global "leaf economic spectrum in subtropical evergreen broad-leaved forests,and a dimension related to leaf thickness and leaf tissue density was also found.There was a multidimensional "root economic spectrum" of fine roots in subtropical evergreen broad-leaved forest.One of dimensionality was closely related to resource acquisition and conservation,and the other two were related to root diameter and root carbon concentration.In subtropical evergreen broad-leaved forest,the coordination between leaf and root functional traits was very strong,and the strong correlation still existed even after the phylogenetic correction,which could predict the underground root nitrogen concentration.