Hydraulic Characteristics Of Woody Plants In A Northern Tropical Seasonal Rain Forest In Guangxi's Southwest Karst Landscape

Tropical seasonal karst rain forest in Southwestern Guangxi is listed as one of the global biodiversity hotspots.This habitat is characterized by large rock outcrops,shallow and patchy soils,rapid infiltration and runoff.Therefore,karst plant species frequently suffer from drought due to limited soil water availability.Plant hydraulic traits are important to clarify the physiological and ecological adaptability of karst plants.In this study,leaf anatomical structure,xylem hydraulic architecture,water potential,hydraulic safety margin,leaf turgor loss point and sapwood density were measured in 17 typical woody plant species co-occurred in a tropical karst seasonal rain forest.We found that(1)Karst woody plants have relatively higher leaf thickness,palisade tissue thickness,and epidermis thickness.(2)There was a large inter-specific variation in xylem water potential at 50%loss of hydraulic conductivity.However,most of them showed narrow and even negative hydraulic safety margin(HSM),indicating a high hydraulic risk in this forest during the dry season.(3)The species distributed on ridges have larger ratio of palisade tissue to spongy tissue(PT:ST)and smaller k,than those in valleys.Shrubs have higher Huber value(HV)than trees and lianas.The HV values of shrubs distributed on ridges were significantly higher than those of in valleys.Evergreens are more resistant to drought-induced cavitation and have lower leaf water potential than deciduous trees,but there was no significant difference in hydraulic efficiency between them.(4)There was no significant correlation between stomatal density(SD)and leaf vein density(VD).Specific leaf area was significantly correlated with water potential and turgor loss point,indicating a co-ordination between leaf hydraulics and economics.There may not be a trade-off between resistance to cavitation and hydraulic conductivity efficient.This may be explained by the diverse hydraulic strategies of karst plants to cope with seasonal drought,e.g.,deep roots,abundant parenchyma cells in xylem,abundant leaf hairs,and regulating of transpiring leaf area.