A Study On Plants Functional Traits During Ontogeny Under Different Water Availability

As the important traits reflecting carbon economy and water transport strategies in plants,economic traits,hydraulic traits and their trade-offs have received much attention.However,few studies have focused on the changes of these two groups of functional traits and their relationship during ontogeny.With the rise of trees height,the hydraulic environment of plants will change greatly due to the influence of external water conditions and internal genetic factors.Therefore,the water use strategies of plants will change accordingly,which will further affect economic traits and individual growth.As a result,it is of great significance to explore the variation patterns of plant functional traits during ontogeny under different water availability conditions,for revealing the response of plant carbon-water economic investment to tree height and understanding how water conditions affect plant growth strategies.The main results of this study are as follows.(1)At different growth stages,economic and hydraulic traits of the Loess Plateau and Qinling Mountains have some similar trends.Large tree stages at both sites showed a significantly larger P_max,LMA,LT,SD,VD and smaller SL,?_tlp,and small tree stages are on the contrary.The obvious differentiation between these two stages indicated that with the growth of trees,the drought resistance and photosynthetic capacity are greatly improved,the growth rate of the plant is accelerated,and the tolerance to the external environment is enhanced.Correlations between functional traits are not always present between different growth stages.Compared with large tree stage,the correlations between economic and hydraulic traits in small tree stage are more and stronger.These results indicate that trees are more sensitive to the environment at the early stage,so they tend to form a more stable trait combination to cope with the environment pressure.(2)Compared with economic traits,the change at ontogenetic level of hydraulic traits during ontogeny in both places is more significant,indicating that hydraulic traits are more sensitive to the rise of tree height.The differences of the hydraulic traits(SD,WD and A_L/A_Sin the middle tree stages between the Loess Plateau and Qinling Mountains are significant,indicating that the individual hydraulic structure at this stage may be more sensitive to different soil water conditions.The important role of tree height should be considered in subsequent studies related to hydraulic characteristics.In the comparative studies between all species and common species at two sites,hydraulic traits showed more differences than economic traits,indicating greater interspecific variation of hydraulic traits.In addition,compared with economic traits,the correlations between hydraulic traits are less correlated in each stage of two regions.(3)Compared with the Qinling Mountains,each plants growth stage of the Loess Plateau has significantly greater LT,TD,and significantly smaller?_tlp,P_max.This is related to the low water availability in the Loess Plateau.Plants can achieve higher drought resistance by reducing transpiration and photosynthetic rate to adapt to water deficit.Comparisons of 12functional traits between common species and all species show that the differences of plant functional traits among species in Qinling Mountains were higher than those in Loess Plateau,especially hydraulic traits.The tradeoff between economic traits(except P_max)in the Loess Plateau is significantly stronger than that in the Qinling Mountains,suggesting that plants could respond to the limited resources by forming a more stable trait combination.(4)There are significant differences in the coupling of economic and hydraulic traits between different growth stages at two sites.Compared with Qinling Mountains,there are more tradeoffs between economy and hydraulic characteristics in the Loess Plateau.The tradeoff relationship in the Loess Plateau become stronger with plant growth,while small and large tree stages in Qinling Mountains have more relationships.There are some similar correlations between large tree stage in Qinling Mountains and small tree stage in Loess Plateau.This may be related to the fact that small tree stage is more sensitive,and the large tree stage in the Qinling Mountains is faced with more intense competition due to the higher species richness,because the stable trade-off relationship of plants can reduce carbon consumption,which is conducive to plants.