Functional Traits Of Absorptive Roots And Leaves Of Lianas In Tropical And Temperate Secondary Forests

Lianas(woody climbers)are an important component of forest resources,and have stronger competition for the same limited resources and wider ecological adaptability compared with trees.With the global climate change and the increasing degree of forest fragmentation caused by anthropogenic logging,the diversity and abundance of lianas have significantly increased in tropical and temperate forests.Such higher diversity and abundance of lianas can reduce tree growth and regeneration,which,in turn,affect forest composition and ecosystem functioning.However,most previous studies on resource competition and acquisition strategies of lianas have mainly focused on the role of leaf functional traits,and worked at tropical regions,the role of root functional traits is overlooked,limiting our understanding of resource acquisition strategies of lianas in different climate environments.In this study,we sampled 69 liana species from two secondary forests in tropical area of Limushan in Hainan and temperate area of Maoershan in Heilongjiang,and measured their functional traits,including root and leaf morphology,anatomy and tissue chemistry.In order to reveal resource acquisition strategies and adaptive mechanisms of lianas in different environments,we analyzed trait variations,trait correlations,the linkages between root and leaf functional traits,and the effect of phylogeny on traits under the different tropical and temperate climate.The main findings are as follows:(1)There were no significant differences of traits in absorptive root morphology,anatomy(i.e.,cortical thickness and stele diameter),tissue chemistry,and mycorrhizal colonization between tropical and temperate secondary forests,but the differences of root branching ratio and xylem vessel were significantly.Compared with tropical lianas,temperate lianas showed higher root branching ratio,xylem vessel diameter and root hydraulic diameter(25%,29% and40% higher,respectively),and lower vessel density(55% lower).Phylogenetically informed principal component analysis(p PCA)showed that lianas had two orthogonal dimensions axes,one was represented by root diameter-specific root length,and another was represented by root tissue density-root nitrogen content,respectively.However,there were some differences of distribution patterns between tropical and temperate lianas in root economics space.Both tropical and temperate lianas had similar strategies for resource absorption,but were different for resource transportation.Compared with tropical lianas,temperate lianas tend to more occupy the side with higher transport efficiency,reflecting the differences in adaptation strategies of the absorptive roots of lianas to different climate environments.(2)Different from the root functional traits,the liana leaf traits of morphology,anatomy and tissue chemistry were significantly differences between tropical and temperate secondary forests.Temperate lianas showed higher specific leaf area and nitrogen content(42% and 31%higher,respectively),and lower tissue density(18% lower);tropical lianas had higher vein density and stomatal density(34% and 71% higher,respectively).p PCA showed that the relationship between economic traits and hydraulic traits of liana leaves decoupled,indicating that the constrained of one function would not affect the other function in leaf physiology when photosynthesis and water loss regulation were carried out at the same time.In leaf hydraulic traits,it was further found that there were two independent trait dimensions of controlling water transport(i.e.,vessel traits)and regulating water loss(i.e.,stomatal traits)in liana leaves,such independency was similar in both tropical and temperate secondary forests.These results suggest that lianas can adapt to environmental changes by controlling the balance between water supply and water loss through many ways and flexible strategies in both tropical and temperate regions.(3)Correlation analysis of single pair traits between liana leaves and roots showed that there were no significant relationships,excepting tissue density in tropical and temperate lianas,and nitrogen content of tropical lianas.By contrast,Canonical correlation analysis(CCA)showed significant correlations among trait combinations between leaves and roots,with variance explained from 17% to 98%.The results of redundancy index revealed that the effects of leaf economic trait combination and hydraulic trait combination on roots in lianas were greater than that of root economic trait combination and hydraulic trait combination on leaves,reflecting that the processes of nutrient and water absorption and transportation in liana roots was restricted by the processes of physiology and ecology in liana leaves.Compared with tropical lianas,the interactions between most leaf and root trait combinations were enhanced in temperate lianas,indicating that the relationship between leaves and roots could be strongly affected by environmental changes.However,leaf hydraulic traits of lianas in temperate regions were more affected by root hydraulic traits,whereas tropical lianas were opposite,suggesting that lianas can adapt to environmental changes at whole-plant level through the trad-off between water uptake(i.e.,root hydraulic trait combination)and water loss(i.e.,leaf hydraulic trait combination).(4)The variation of functional traits in liana leaves and roots was also affected by plant phylogeny,but such effect varied greatly between leaf and root traits,between tropical and temperate lianas.The proportion of significant phylogenetic signals in tropical liana leaf and root traits(52% and 26%,respectively)was great higher than that of temperate lianas(28%and 0%,respectively),indicating that functional traits of tropical lianas had relatively strong phylogenetic conservatism.By contrast with roots,leaf functional traits displayed relatively more phylogenetic signals in tropical and temperate lianas,suggesting that plant evolution had a greater effect on the variation of leaf functional traits than on roots.The weaker phylogenetic signals in liana root traits can break the constraint of plant lineages,and might facilitate the evolution of flexible below-ground ecological strategies that allow them to cope with changing environments.In addition,there was no significant correlation between most functional traits and angiosperm divergency time(at family level)in liana leaves and roots,but leaf thickness,root vessel diameter and guard cell length were closely related to the divergency time.These results suggest that early and late evolved lianas still have different strategies in environmental adaptation and resource competition,which further confirmed that the stronger ecological adaptability of lianas may be related to their unconstrained by evolutionary history.In conclusion,this study,for lianas,confirmed that the environmental changes from the tropic to temperate had relatively little effect on functional traits of absorptive roots,but had relatively large effect on leaf functional traits,and as well as a great effect on the relationship between leaves and roots.Both leaves and roots of lianas showed multi-dimensional trait relationships,which may enable lianas to flexibly adjust their traits to adapt to environmental changes.The weak phylogenetic constraint of liana roots may,in turn,enhance the advantages in resource competition and ecological adaptation.These results from liana study were important for understanding the resource acquisition strategy,the mechanism of adapting to environmental changes,enriching the ecology of lianas,and enhancing the level of sustainable management in forest ecosystem with different plant life forms in the context of global climate change.