Graduate School of Environmental Science, Okayama University, Okayama 700-8530, Japan.
Tree Physiol. 2013 Apr;33(4):335-44. doi: 10.1093/treephys/tpt010. Epub 2013 Mar 14.
Woody species hydraulically vulnerable to xylem cavitation may experience daily xylem embolism. How such species cope with the possibility of accumulated embolism is unclear. In this study, we examined seven temperate woody species to assess the hypothesis that low cavitation resistance (high vulnerability to cavitation) is compensated by high recovery performance via vessel refilling. We also evaluated leaf functional and xylem structural traits. The xylem recovery index (XRI), defined as the ratio of xylem hydraulic conductivity in plants rewatered after soil drought to that in plants under moist conditions, varied among species. The xylem water potential causing 50% loss of hydraulic conductivity (Ψ50) varied among the species studied, whereas only a slight difference was detected with respect to midday xylem water potential (Ψmin), indicating smaller hydraulic safety margins (Ψmin - Ψ50) for species more vulnerable to cavitation. Cavitation resistance (|Ψ50|) was negatively correlated with XRI across species, with cavitation-vulnerable species showing a higher performance in xylem recovery. Wood density was positively correlated with cavitation resistance and was negatively correlated with XRI. These novel results reveal that coordination exists between cavitation resistance and xylem recovery performance, in association with wood functional traits such as denser wood for cavitation-resistant xylem and less-dense but water-storable wood for refillable xylem. These findings provide insights into long-term maintenance of water transport in tree species growing under variable environmental conditions.
木质部易发生空穴化的 Woody 物种可能会经历每日木质部栓塞。这些物种如何应对可能积累的栓塞尚不清楚。在这项研究中，我们研究了七个温带木本物种，以检验以下假说：即低空穴化抗性（对空穴化敏感）可通过导管再填充来实现高恢复性能来补偿。我们还评估了叶片功能和木质部结构特征。木质部恢复指数（XRI）定义为土壤干旱后重新浇水的植物的木质部导水率与湿润条件下的植物的木质部导水率之比，在物种间存在差异。引起木质部导水率损失 50%的木质部水势（Ψ50）在研究的物种间存在差异，而中午木质部水势（Ψmin）的差异很小，表明对空穴化更敏感的物种的水力安全裕度（Ψmin - Ψ50）更小。空穴化抗性（|Ψ50|）与物种间的 XRI 呈负相关，对空穴化敏感的物种在木质部恢复方面表现出更高的性能。木材密度与空穴化抗性呈正相关，与 XRI 呈负相关。这些新结果表明，在与木材功能特性相关的情况下，如抗空穴化的木质部具有更密集的木材，以及可再填充的木质部具有较不密集但可储存水的木材，空穴化抗性和木质部恢复性能之间存在协调关系。这些发现为了解在变化的环境条件下生长的树种的长期维持水分运输提供了线索。
