长白山阔叶树种木质部环孔和散孔结构特征的分化导致其水力学性状的显著差异

木质部的解剖结构特征对树木水分传输功能有重要的影响,阔叶树种木质部环孔和散孔结构特征的分化,很可能导致两个功能类群在水力学结构上存在显著差异,但是有关两个功能类群间细致的水力学性状的对比研究还较少,二者整枝水平的导水率及纹孔水平的细致结构差异尚未见报道.本试验以长白山阔叶红松林常见的3个环孔材和4个散孔材乔木树种为研究对象,对比了两个功能类群树种的整枝导水率(k_shoot)、枝条木质部栓塞脆弱性(p_50)等重要水力学相关生理功能特征,并分析了两个功能类群间的木质部组织水平和纹孔水平上的解剖结构特征差异.结果表明:与茎段导水率差异一致,环孔材树种的整枝导水率也显著高于散孔材,但枝条木质部气穴化抵抗力显著弱于散孔材,二者的差异反映了整枝水平上木质部导水效率和安全性之间的权衡关系,与两个功能类群的水力学生理特征存在显著差异一致,二者在最大导管长度、导管直径、纹孔开口面积、纹孔开口比例等光学和扫描电镜观测解剖结构特征上都存在显著差异;木质部解剖特征(组织水平、纹孔水平)和k_shoot、p_50等生理特征间,以及木质部不同解剖特征之间存在显著的相关,且两个功能类群遵循相同的规律,反映了木质部结构对水分传输功能的重要影响,而导水率和气穴化抵抗力对木质部对立的结构要求,体现了树木水分传输系统构建的生物物理局限性.

Divergence between ring- and diffuse-porous wood types in broadleaf trees of Changbai Mountains results in substantial differences in hydraulic traits.

Hydraulic characteristics of trees are strongly influenced by their xylem structures. The divergence in wood type between ring-porous and diffuse-porous species is expected to lead to significantly different hydraulic architecture between these two functional groups. However, there is a lack of comprehensive comparative studies in hydraulic traits between the two groups, in that no study has compared the whole-shoot level hydraulic conductance and detailed pit-level xylem anatomy has not been reported yet. In the present study, detailed hydraulic related traits were stu-died in three ring-porous and four diffuse-porous tree species commonly found in the broadleaf tree species of the Changbai Mountains, including whole-shoot hydraulic conductance (K_shoot), resis-tance to drought-induced embolism (P₅₀), and detailed tissue- and pit-level anatomical characteristics. Our results showed that: 1) consistent with the differences in stem hydraulic conductivity, ring-porous species showed significantly higher K_shoot but significantly lower resistance to drought-induced embolism, i.e., higher P₅₀, indicating a trade-off between hydraulic efficiency and safety in those two functional groups; 2) consistent with their significant divergence in hydraulic functions, the two functional groups showed significant differences in a suite of xylem anatomical characteristics at both the tissue and pit levels, such as maximum vessel length, vessel diameter, pit aperture area and aperture fraction; 3) significant correlations were identified between xylem structural characteristics and between structure and functions across both functional groups, indicating that differences in hydraulic functions were underlain by divergences in a suite structural traits. The competing structural requirements between different hydraulic traits, such as between shoot hydraulic conductance and resistance to drought-induced embolism, reflected the biophysical constraints of xylem design that could not fulfill multiple requirements of xylem functioning at the same time.