Study On Hydraulic Traits Of Typical Deciduous Trees And Shrubs In Loess Hilly Region

Plant hydraulic traits is an important aspect of plant water relations, and directlydetermine plant drought-tolerance and whole-plant water use. In this paper, taking thetypical native deciduous woody plants growing on the Loess hilly region as the materials,we explored the relationship between leaf traits and Pressure-Volume curve parametersof eleven woody species, the hydraulic architecture traits of three tree species fromdifferent successional stages and of four shrubs. The main purposes were to reveal therelationship between the leaf functional traits and the physiological drought tolerance ofthe typical woody plants in this area and to clarify the hydraulic architecture differencesof the typical trees and shrubs and their anatomical basis, thus to provide certaintheoretical basis for the restoration and reconstruction of degraded ecosystems on theLoess Plateau. The main results were as follows:（1）Among the leaf traits of the eleven tested species, leaf mass per area（LMA）was positively correlated with leaf density（LD）but uncorrelated with leaf thicknes（sLT）,LD was negatively correlated with LT. Osmotic potential at turgor loss point（Ψtlp）waspositively correlated with saturated osmotic potentia（lΨsat）and negatively correlated withbinding water proportion（B）across tested species. Canonical correlation and Pearsoncorrelation indicated that there was relation between leaf traits group and PV parametersgroup, LMA was negatively correlated with relative water content at turgor loss point（RWCtlp）and close to negatively correlated with LD. All these showed that LMAvariation was caused by LD rather than LT, there was a tradeoff relationship between LDand LT. Solutes accumulation was the major reason of decreased Ψtlp. Higher LMA was was associated with lower RWCtlp, demonstrating the physiological basis of species withhigher LMA also have stronger drought-tolerance.（2）Quercus liaotungensis had lower Ψsat, Ψtlp, RWCtlpand higher leaf capacitance（Cleaf）than Populus davidiana and Betula platyphylla. Quercus liaotungensis hadhigher maximum Ksand lower HV than early succession species Populus davidiana andBetula platyphylla, thus maximum Klfor these three species was the same. For both leafand branch, Quercus liaotungensis was more resistant to embolism than Populusdavidiana and Betula platyphylla, meanwhile, Quercus liaotungensis also had a largerhydraulic safety margin when balanced by the difference of minimum leaf waterpotential during dry season （Ψmin）and xylem water potential corresponding to50%lossof conductivitie（sΨ50）, and larger leaf hydraulic protection for branch when estimated bythe difference between leaf Ψ50and branch Ψ50. No hydraulic architecture difference wasfound for two early succession species Populus davidiana and Betula platyphylla. Theseresults demonstrated from plant hydraulics that higher dehydration tolerance, larger leafcapitance, stronger leaf and branch embolism resistance, higher hydraulic safety atQuercus liaotungensis may be responsible for its higher drought tolerance than erarlysuccession species Populus davidiana and Betula platyphylla.（3）The twig branches of Sophora viciifolia had the largest maximum hydraulicconductivity（Ks-max）among the four typical shrubs in Ziwuling forest zone, followed byHippophae rhamnoides, Prunus davidiana and Rosa xanthina. Rosa xanthina had thestrongest xylem cavitation resistance, followed by Prunus davidiana, Hippophaerhamnoides and Sophora viciifolia. Across the four tested shrubs, Ks-maxwas positivelycorrelated with the mean diameter of vessel lumen and hydraulic diameter of vessellumen and negatively correlated with conduit density and wood density. Meanwhile, thecavitation resistance was negatively correlated with the mean diameter of vessel lumenand wood density. All these results indicated that: conduit diameter and wood densitywere key factors affecting the hydraulic conductivity and the cavitation resistance of thetypical shrubs on the Loess Hilly Area.