兰科植物根的结构功能及其生态适应意义

The Orchidaceae family is of great economic importance to floral and pharmaceutical industries as well as one of the most endangered plant taxa. Understanding of how orchids adapt to the environments is essential for their conservation and utilization. Because root is the principal water- and nutrient-absorbing organ, it has a great impact on the growth and ecological adaptation of a plant. Because of low availability of substrates in epiphytic habitats, epiphytic orchids may experience restricted and irregular moisture and nutrient supplies. It is speculated that root may play an important role in adaptation of epiphytic orchids to water and nutrient stresses. However, such knowledge is limited. Over the past 5 years, we have conducted systematic researches on leaf anatomy and physiology of more than 60 members of the Orchidaceae family. Thus, the present project will mainly focus on the structures and functions of roots in terrestrial orchids and epiphytic orchids by using field investigations and controlled experiments. The main research contents include: (1)what are the key differences in root structures and functions between terrestrial orchids and epiphytic orchids? How do the structures and functions of orchid roots respond to the environments? (2)what are the impacts of root structure, aquaporin and abscisic acid on water uptake and transport of orchid plants? (3)what are the influences of root structure and symbiotic fungi on the nutrient uptake and utilization of orchid plants? (4)how do orchid plants coordinate the functions of root, pseudobulb and leaf to cope with environmental stresses. Understanding of the above questions will address the functional roles of root in the adaptation of orchid plants to water and nutrient. The outputs of this project will provide novel knowledge on the conservation and utilization of species resources in Orchidaceae. Five papers including 4 SCI papers will be published, and three graduate students will be trained through implementing this project.

兰科具有重要的观赏和药用价值，也是重要的保护植物，生态适应性的阐明将有助于其物种资源的保护和利用。根是主要的水分和养分获取器官，对植物的生长及环境适应有重要影响。附生兰科植物生长在水分和养分供应极不稳定的生境中，推测根在其水分和养分适应中具有重要作用，但人们对此的认识甚少。申请者已对兰科植物叶片的生态适应意义开展了系统研究。本项目将以根为重点，利用野外观测和控制实验对地生兰和附生兰进行比较，回答以下四个科学问题：(1)地生兰和附生兰根的形态结构差异及其与环境的关系如何？(2)根的形态结构、水孔蛋白和脱落酸怎样调节兰科植物的水分吸收与输导？(3)根形态结构及共生真菌如何影响兰科植物的养分获取与利用？(4)兰科植物在不同生境中如何协调根、假鳞茎和叶片的功能？通过对这些问题的研究，揭示根在兰科植物水分和养分适应中的作用，为物种资源的保护与利用提供理论依据。发表研究论文5篇，培养研究生3名。

兰科是形态结构和生态适应特征最为多样的植物类群之一，具有重要的观赏、药用和保护价值，生态适应性的认识将为其物种资源的保护利用提供理论基础。兰科植物地生型与附生型物种所处的生境和能够利用的资源明显不同，暗示其生态适应性存在差异。根是主要的水分与养分吸收器官，其结构功能对植物的资源获取和生态适应有重要影响。项目利用野外观测和控制实验，研究了兰科地生型和附生型植物根的结构功能及其生态适应意义，取得的主要结果包括：（1）附生型和地生型兰科植物根性状的主要差异为根半径和根被占半径的比例，附生兰倾向于构建更高比例的根被以维持植株的水分平衡和增强对附生生境的适应；（2）附生兰科植物通过在根的不同空间上形成类角质层与发育根毛实现“功能分区”，解决根被在增加水分吸收和减少水分散失上的功能冲突；（3）根被的形成受细胞程序化死亡过程控制，该过程包括细胞程序化死亡启动、次生细胞壁增厚和细胞死亡后自溶三个阶段；（4）束花石斛的根对水分胁迫比叶片更敏感，干旱和光照均对ABA合成有显著影响，根系能通过快速的ABA合成和抗氧化酶诱导增强束花石斛对水分胁迫的适应；（5）独蒜兰属植物的菌根菌主要为胶膜菌科、角担菌科、腊壳耳目、小纺锤菌目和木耳目，白花独蒜兰的石附生型和树附生型个体有相似的胶膜菌科操作分类单元（OTUs），但有不同的蜡壳耳目OTUs，不同生境存在一定程度的真菌特异性；（6）西藏虎头兰能灵活利用假鳞茎内储存的水和碳，无叶假鳞茎中的储水对相连分株的叶片光合作用维持有重要贡献；（7）环境因子对石斛属植物中大部分根和叶片性状的影响大于系统发育，根与叶性状间较强的关联性有助于维持整株植物的水分平衡和提高水分利用效率。项目发表SCI论文8篇，培养研究生5名。研究结果为认识兰科植物的生态适应和促进物种资源的保护利用奠定了重要基础。