Study On The Root Tips’ Functional Traits Of 18 Climbing Plants In Tropical Forest

Climbing plants,including lianas and vines,are a group of plants that grow upward by climbing or twining around host trees.As an important part of tropical forests,climbing plants have an important influence on the structure and function of the forest ecosystem through competition with trees.But little is known about root functional traits of climbing plants.In this study,12 species of lianas and 6 species of vines were selected from a tropical forest of Hainan,and the morphological traits,tissue chemical traits,anatomical structure and mycorrhizal colonization of root tips of these climbing plants were measured.The purpose of this study is to investigate the differences in functional traits of root tips and their linkages among species and between life-forms of climbing plants,attempting to reveal the distribution patterns of structure and function of root tips of climbing plants in tropical forests.The main results are as follow:1)There were significant interspecific differences in root tip diameter,cortex thickness,and stele diameter(p<0.05).Cortical thickness of root tips of climbing plants showed a consistent distribution pattern to root tip diameter.Compared with cortical thickness,the distribution of stele diameter was more dependent on specific species.For both vines and lianas,root tip diameters were significantly positively correlated with cortical thickness and stele diameter among species(p<0.05),and the correlations between root diameter and cortical thickness were both stronger than that between root diameter and stele diameter,with stronger correlation in vines than lianas(root diameter&cortical thickness:vines R~2=0.98,lianas R~2=0.96;root diameter&stele diameter:vines R~2=0.77,lianas R~2=0.70).The correlations of cortex thickness and stele diameter with their respective anatomical components in root tips highly relied on species and life-forms,with significant relationships only found between cortex thickness and the number of cortical cell layers in vines,and between cortex thickness and mean diameter of cortical cell,stele diameter and the number of conduits per stele in lianas.2)In root tips,specific root length(SRL),tissue density(RTD),and specific surface area(SRA)showed significant differences among 18 climbing plants(p<0.05).Higher values of these three morphological traits were all found in lianas rather than in vines,but the differences between life-forms were not significant(p>0.05).Among different species of a life-form,root tip SRL showed significant and positive correlations with SRA,and the correlations were stronger in lianas(R~2=0.95).In contrast,the correlations between SRL and RTD,and between SRA and RTD were both negative and significant in root tips of lianas,but not significant in vines.3)There were significant interspecific differences in total carbon(C)and total nitrogen(N)concentrations,and C:N ratio in root tips of 18 climbing plants.Compared with vines,lianas possessed higher total C and total N concentrations,and lower C:N ratio,but the differences in these chemical traits were not significant between life-forms(p>0.05).There is no significant correlation between total C and total N concentrations in root tips of climbing plants.4)The mycorrhizal colonization rate and degree differed significantly among 18species,with the highest rate of 100%and the lowest rate of 0%for some species.However,the highest rate of mycorrhizal colonization did not equal to the highest degree of colonization,and a significant positive correlation between mycorrhizal colonization rate and degree was found in lianas,but not in vines.Among the species colonized with a single type of mycorrhizal fungi,lianas were mostly colonized by Ectomycorrhiza but vines were mostly colonized by Arbuscular mycorrhiza.However,mycorrhizal colonization types do not appear to be affected by life-forms of climbing plants or by mycorrhizal colonization rate and degree.5)The correlation analysis and principal component analysis results showed weak relationships among morphological traits,tissue chemical traits,anatomical structure and mycorrhizal colonization.The functional traits distributed on the three main dimensions were different between the two life-forms,with a higher explanation of vines(87.5%)than lianas(71.4%)for the total variance.18 climbing plants can be classified into four categories through the cluster analysis based on the root tips’functional traits,and there are differences among the superior traits possessed by each type of climbing plant.