兴安落叶松针叶解剖结构变化及其光合能力对气候变化的适应性

叶片易受环境因子影响，其形态解剖结构特征不但与叶片的生理功能密切相关，而且反映树木对环境变化的响应和适应。叶片结构的改变势必会改变树木的生理功能。同一树种长期生长在异质环境条件下，经过自然选择和适应，会在形态和生理特性等方面产生变异，形成特定的地理种群。另外，母体所经受的环境胁迫也会影响到其子代的生长、发育和生理等特征。因此，了解植物叶片形态结构对环境变化的响应与适应是探索植物对环境变化的响应适应机制的基础。兴安落叶松(Larix gmelinii Rupr.)是我国北方森林的优势树种，主要分布在我国东北地区，但日益加剧的气候变化可能会改变其现有的分布区。为了区分叶片对气候变化的可塑性和适应性，本研究采用同质园法比较测定了6个不同气候条件下的兴安落叶松种源的32年生树木的针叶解剖结构和光合生理相关因子，利用石蜡切片方法分析了针叶的解剖结构特征、光合能力（Pmax-a）、水分利用效率（WUE）之间的关系及其对气候变化的适应性。结果表明：表皮细胞厚度、叶肉细胞厚度、传输组织厚度、维管束厚度、内皮层厚度以及叶片总厚度均存在显著的种源间差异（P < 0.05）。叶肉细胞厚度与Pmax-a、气孔导度和WUE之间均存在显著的正相关关系（P < 0.05）。叶肉细胞厚度、表皮细胞厚度、叶片总厚度以及叶肉细胞厚度和表皮细胞厚度在叶片总厚度中所占比例均与种源地的干燥度指数（即年蒸发量与年降水量之比）呈正线性关系。这些结果说明：不同种源兴安落叶松针叶解剖结构因对种源原地气候条件的长期适应而产生显著的差异，从而引起其针叶光合作用、水分利用等生理功能发生相应的变化,从而有利于该树种在气候变化的情景下得以生存和繁衍。

Variations in leaf anatomy of Larix gmelinii reflect adaptation of its photosynthetic capacity to climate changes

Leaf anatomy, being susceptible to environmental factors, is closely related to physiological functions of the leaf, and also reflects responses and adaptation of the tree to environmental changes. Changes in leaf anatomical structure are bound to change the physiological functions of trees. The same species growing in heterogeneous environment for a long time through natural selection and adaptation will result in the variation in morphological and physiological characteristics, forming particular geographic populations. In addition, Matrix subjected to environmental stress will affect its offspring growth, developmental and physiological characteristics. Therefore, to understand how the morphological structure of leaves respond and adapt to environmental changes is essential for exploring the response and adaptation mechanism of plants to environmental changes Dahurian larch (Larix gmelinii Rupr.) is a dominant tree species in boreal forest in China, mainly distributed in the northeast of China. However, further climate changes may change its existing distribution area. However, it is difficult to distinguish short-term responses of leaf anatomy and physiology from their potential long-term adaptation to climate changes in field. In this study, we conducted a common garden experiment that included six provenances of Dahurian larch with different climate and site conditions, three replicate trees each provenance. The trees were 32 years old, seeded in 1980, and transplanted in 1983 at identical site and climate conditions. We measured parameters of leaf anatomical properties using paraffin section method (i.e., total leaf thickness LD], leaf adaxial epidermis cells thickness LUPD], leaf abaxial epidermis cells thickness LBPD], leaf adaxial mesophyll cells thickness LUCD],, leaf abaxial mesophyll cells thickness LBCD] Leaf vascular bundle tissue thickness LVD], leaf endoderm cells thickness LED], leaf transporting tissue thickness LTD], leaf epidermis cells thickness LPD], leaf mesophyll cells thickness LCD], and photosynthetic physiology (i.e., photosynthetic capacity Pmax-a], stomatal conductance gs], water use efficiency WUE]) in order to address the question of whether leaf anatomical structure adapts to climate changes and consequently results in physiological adaptation. The results showed that the thickness of epidermis cells, mesophyll cells, transmission tissue cells, vascular cells and endothelial cells, and the total thickness of the needles differed significantly among the provenances (P < 0.05). There was a significant difference in the proportion of thickness of each anatomical part. The thickness of mesophyll cell accounted for the largest proportion, with an average proportion ranging from 38.4 % to 43.3 %. The thickness of mesophyll cells was positively correlated (P < 0.05) with Pmax-a, gs, and WUE. The thickness of mesophyll cells and epidermal cells, the total thickness of the needles, and the proportions of thickness of mesophyll cells or epidermal cells in the total thickness of the needle were all positively correlated with the aridity index (the ratio of mean annual evaporation to mean annual precipitation) at the origin sites of the provenances. These results suggest that needles of the Dahurian larch trees from different provenances alter their anatomical structures significantly due to adaptation to local climate conditions, and accordingly change their physiological functions such as photosynthesis and water use efficiency.