乔木和灌木枝水分传导脆弱性沿降水量递增的分化

植物枝条失去50%水分传导时对应的水势(ψ50),称为枝的水分传导脆弱性。该指标是反映植物干旱适应能力的关键指标,也决定着植物沿降水梯度的分布。乔木和灌木枝水分传导脆弱性沿降水量递增的变化是否一致,有待揭示。基于已发表的文献,筛选出236种乔木、137种灌木,建立ψ50与分布地年均降水量及分布地干旱指数关系,来确认两大类植物的ψ50沿降水递增的变化的异同。结果表明:乔木和灌木的ψ50均随降水梯度、干旱指数的增加而增加,一元线性回归方程显著;ψ50与降水梯度、干旱指数回归方程的回归系数在乔木和灌木间差异不显著,但同一降水量下,乔木比灌木具有较低的ψ50值。我们认为灌木和乔木枝水分传导脆弱性对降水量和干旱指数递增具有相似的适应性。

Divergence in Stem Hydraulic Vulnerability of Trees and Shrubs along A Precipitation Gradient

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.