Leaf trait variations and relationships of three Acer species in different tree sizes and canopy conditions in Xiao Hinggan Mountains of Northeast China
Aims Leaf traits are affected not only by plant sizes,but also by different canopy conditions where mature trees and saplings grow.Thus,these trees choose various survival strategies to adapt to different canopy conditions by adjusting their leaf traits.The aim of this study is to investigate the changes of leaf traits of three Acer trees along with the changes of plant size and canopy condition.Methods In this study,three species(Acer ukurunduense,A.tegmentosum and A.pictum subsp.mono)in broadleaf Pinus korainesis forest in Xiao Hinggan Mountains of Northeast China were selected.Six leaf economics spectrum traits,specific leaf area(SLA),leaf dry matter content(LDMC),leaf thickness(LT),chlorophyll(Chl)content,net photosynthetic rate per area(Aarea)and non-structural carbohydrates(NSC)content,together with two defensive traits,total phenolics(TP)content and flavonoids(FLA)content of adult trees and saplings in gaps and saplings in understory were measured.Whether leaf traits and their relationships varied with plant sizes and canopy conditions was further analyzed to illustrate how gaps influence forest regeneration by altering leaf traits,and to explore the differentiation of survival strategies for plant individuals growing under various habitats.Important findings Adults in gaps had higher LDMC,Chl content,FLA content and NSC content compared with saplings in gaps,which meant adults had adequate photosynthetic accumulation and they were more capable to defend against herbivory.LDMC,LT,Chl content and Aarea of gap saplings were significantly higher than saplings in understory,indicating that canopy condition was a vital source of leaf trait variations.The absolute slope of relationship between SLA and LDMC for adults was significantly higher than that for saplings in gaps,but the absolute slope of understory saplings was significantly lower than that of the gap saplings.The relationship between defensive traits remained stable among different plant sizes and canopy conditions.These evidences showed that,adults invested more in leaf construction such as leaf thickness and defensive substances,so they chose"conservative"strategy.Saplings in understory improved their ability to acquire light by increasing SLA,they therefore tended to choose"acquisitive"strategy.Saplings in gaps however,showed the transition strategy between"conservative"and"acquisitive"strategies.Results further indicated that,when saplings were not limited by light,their photosynthetic rate increased rapidly to be significantly higher than that of adults.In addition,forest gaps can promote the regeneration of forest stand by enhancing the abilities of photosynthesis and resistance to herbivory of saplings.
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