Variations And Interrelationships Of Foliar Economics And Hydraulic Traits For Larix Gmelinii In Different Site Conditions

Variations and potential trade-off of leaf economics and hydraulic traits are essential for assessing and predicting the effect of climate change on tree survival,growth and distribution,and also important for modeling carbon-water coupling and extending the leaf economics spectrum.This study was conducted at the Maoershan Forest Ecosystem Research Station.A transect of 27 year-old Dahurian larch(Larix gmelinii)plantation was established that consisted of five plots extending from the valley to the ridge of a slope,where the leaf nutrient,structural,photosynthetic and hydraulic traits were measured with the aim to explore variations and interrelationships of leaf economic and hydraulic traits.The main results were below:(1)There were significant intra-specific differences in the leaf economics traits in different site conditions(p<0.05).From valley to ridge,leaf mass per area(LMA),mass-based leaf nitrogen concentration(Nmass)and dark respiration rate(Rmass)emerged "low-high-low" pattern,while mass-based leaf photosynthetic rate gradually decreased.Only LMA significant positively correlated with Nmass.Area-based leaf economics traits,including area-based leaf photosynthetic rate(Aarea),leaf nitrogen concentration(Narea)and dark respiration rate(Rarea),were significant difference among the plots and also showed "low-high-low"pattern from valley to ridge,and related to each other.The range of LMA,Amass and Nmass variations are 1.3%,5.3%and 11.3%of the global range,respectively.All results above indicted that there were significant phenotypic variations of leaf economics traits of larch responding different site condition,and we should not ignore the effect of intra-species leaf traits variations on establishing global leaf economics spectrum.Comparing with global leaf economics spectrum,the lower LMA values and defoliation of larch represented the "fast"investment and return strategy,which contrast to the other conifer species.Our results suggested that the relationships of area-based leaf economics traits were closer than that in mass-based of larch,which indicated that using area-based leaf economics traits could be more accurately to predict intra-species variations of deciduous species which leaf longevity ranges more narrowly than evergreen species.Leaf economics traits of larch were major driven by soil nutrient concentration,while didn’t relate to soil water supplying.(2)In response to changes in the site condition,the leaf hydraulic traits also showed significant difference(p<0.05,except for the leaf water capacitance).In the valley where supplying more soil water to larch(Ψfpre higher,predawn leaf water potential),the larch showed higher leaf hydraulic conductance(Kieaf),but more vulnerability embolism(P50 higher,leaf water potential inducing 50%loss of leaf hydraulic conductance)than ridge where Ψpre showed lower.Whether area-based(Karea)or mass-based(Kmass)leaf hydraulic conductance were significantly(p<0.05)correlated with P50,suggesting that a trade-off between hydraulic efficiency and safety existed within the species.P50 was significant positively related with leaf water potential at the turgor loss point(TLP),indicating water transport in xylem and out-xylem path of leaf coordinated to some degree.With soil supplying water capacity increasing,Kleaf and P50 increased,suggested that species that developed in more soil water plots can transport more water to the site where replacing more leaf transpiration water loss,while they were more vulnerable to resistant drought stress.The coordination between leaf hydraulic traits and the intra-species variation of larch provided physiological basics for them to well acclimate varied water condition.(3)Although the strong relationships among traits existed within each groups,leaf economics and hydraulic traits were weak correlation.Overall,after separating the effect of tree height on leaf hydraulic traits,only Kmass and Rmass were positively relation,demonstrating that carbon and water decoupled within one species.Principle analysis(PCA)further indicated that the PCA axis 1 showed strong positive loadings for leaf economics(Aarea,Nmass,Narea)LMA),while the PCA axis 2 had negative loadings for leaf hydraulic traits(Kmass,Karea,P50)and water use efficiency.These results suggested that leaf economic traits and hydraulic traits can vary independently within larch.Multiple trait dimensions may better enable larch to adapt different environment by more freedom developing traits coordination,promoting diverse plant strategies.