Research over the past three decades has shown that stem hydraulic vulnerability, the stem water potential that induces 50% loss of leaf hydraulic conductance(ψ50), is important in influencing species' distribution along a mean annual precipitation(MAP) gradient. However, whether there is divergence in stem hydraulic vulnerability between trees and shrubs along MAP gradient still need to be investigated. In this study, the data set was compiled from published papers, including 236 tree species, and 137 shrub species along a MAP gradient from less than 300 mm to more than 4 000 mm, and then ψ50 of trees and shrubs were tested against MAP and aridity index, respectively. The results showed that values of hydraulic vulnerability to drought in stem of trees and shrubs increased strongly(became less negative) with increasing MAP and increasing aridity index, and coefficients of regression of ψ50 against MAP, and of ψ50 against aridity index between trees and shrub were not significant different. However, at given precipitation, ψ50 of trees is relatively lower than that of shrub. The results suggest that stem hydraulic vulnerability of trees and shrubs have the same adaptation to increasing precipitation and aridity index, and trees are not more vulnerability to drought stress then shrub.
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