Department of Wood Anatomy and Utilization, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, P.R. China.
Wood Collections (WOODPEDIA), Chinese Academy of Forestry, Beijing 100091, P.R. China.
Tree Physiol. 2022 Jun 9;42(6):1216-1227. doi: 10.1093/treephys/tpab174.
Investigating the responses of plant anatomical traits of trees to drought-rewatering cycles helps us to understand their responses to climate change; however, such work has not been adequately reported. In this study, Ginkgo biloba L. saplings were subjected to moderate, severe, extreme and lethal drought conditions by withholding water according to the percentage loss of hydraulic conductivity (PLC) and rewatering on a regular basis. Samples of phloem, cambium and xylem were collected to quantify their cellular properties including cambium and phloem cell vitality, xylem growth ring width, pit aspiration rates and pit membrane thickness using light microscopy and transmission microscopy. The results showed that the mortality rate of G. biloba saplings reached 90% at approximately P88 (xylem water potential inducing 88% loss of hydraulic conductivity). The onset of cambium and phloem cell mortality might be in accordance with that of xylem embolism. Close negative correlations between xylem water potential and PLC and between xylem water potential and cambium and phloem mortality suggested that xylem hydraulic traits are coupled with anatomical traits under declining xylem water potential. Cambium and phloem cell vitality as well as xylem growth ring width decreased significantly with increasing drought conditions. However, xylem pit membrane thickness, cambial zone width and cambial cell geometry were not affected by the drought-rewatering cycles. The tracheid radial diameter, intertracheid cell wall thickness and tracheid density decreased significantly during both drought conditions and rewatering conditions. In addition to hydraulic traits, cambium and phloem cell vitality can be used as anatomical traits to evaluate the mortality of G. biloba under drought. Future work is proposed to observe the dynamics of pit aspiration rates under drought-rewatering cycles in situ to deepen our understanding of the essential role of bordered pits in the 'air-seeding' mechanism.
研究树木解剖结构特征对干旱-复水周期的响应有助于我们了解它们对气候变化的响应；然而，此类工作尚未得到充分报道。在这项研究中，通过根据水力传导率损失百分比（PLC）停水并定期复水，将银杏幼苗置于中度、重度、极端和致死干旱条件下。收集韧皮部、形成层和木质部的样本，使用光镜和透射电镜定量测量它们的细胞特性，包括形成层和韧皮部细胞活力、木质部生长轮宽度、纹孔抽吸率和纹孔膜厚度。结果表明，当木质部水势诱导水力传导率损失 88%左右时（xylem water potential inducing 88% loss of hydraulic conductivity），银杏幼苗的死亡率达到 90%。形成层和韧皮部细胞死亡的开始可能与木质部栓塞的开始一致。木质部水势与 PLC 之间以及木质部水势与形成层和韧皮部死亡率之间呈密切负相关，表明在木质部水势下降的情况下，木质部水力特性与解剖学特性相关联。随着干旱条件的增加，形成层和韧皮部细胞活力以及木质部生长轮宽度显著下降。然而，木质部纹孔膜厚度、形成层区宽度和形成层细胞几何形状不受干旱-复水周期的影响。在干旱和复水条件下，导管径向直径、导管间细胞壁厚度和导管密度都显著降低。除了水力特性之外，形成层和韧皮部细胞活力也可以作为解剖学特征来评估银杏在干旱下的死亡率。未来的工作是建议在干旱-复水周期中观察纹孔抽吸率的动态，以深化我们对具缘纹孔在“空气播种”机制中的重要作用的理解。
