兰属附生植物的水分适应特征

Cymbidium, known as "Chinese orchid", is one of the traditional famous flowers in China. About 2/3 Cymbidium species are epiphytes, growing on the stems and branches of trees. As lack of buffer medium in epiphytic habitats, epiphytes are usually more sensitive to disturbance and environmental change than terrestrial plants. In fact, human activity and environmental change (especially precipitation) exert unprecedented stresses on the natural populations of Cymbidium. Water stress is considered to be a primary factor affecting the population dynamics of epiphytes. However, the ecophysiological mechanisms whereby how water stress affects the growth and survival of epiphyte remain unclear. The present project will compare the differences in molecular, physiological and morphological adaptations to water availability between epiphytic and terrestrial species in Cymbidium by field investigations and controlled experiments. The main objectives are to understand: (i) the relative contributions of various water sources (rainfall, fog, storage water in plant organs) to the maintenance of physiological functions in epiphytic Cymbidium in the rainy and dry seasons; (ii) the morphological, physiological and molecular adaptations of epiphytic Cymbidium to water stress; (iii) the relative roles of plant hydraulics and carbon balance in the growth and survival of epiphytic Cymbidium during drought period. This project will illustrate the adaptive mechanisms of epiphytic Cymbidium to water availability, and provide valuable knowledge for the conservation and utilization of Cymbidium germplasm. 6 SCI papers will be published and 2 graduate students will get trained through implementing the project.

兰属(Cymbidium)植物为中国传统名花，其中2/3的种类是生于树干上的附生兰。因附生环境缺少缓冲基质，附生植物对干扰和环境变化敏感。事实上，人类活动及环境变化正使兰属植物种群承受着巨大的生存压力，生态适应性的研究将有助于更好地保护和利用好这些珍贵资源。水分被认为是影响附生植物生长存活的关键环境因素，但相关的生理生态机制仍不清楚。项目将利用野外及控制实验，通过对兰属附生种与地生种的比较，从分子、生理和形态多个层次，研究(i)各种水源(雨水、雾水、植物自身储水)在旱季对兰属附生植物生理功能维持的相对贡献；(ii)兰属附生植物响应水分胁迫的分子、生理及形态策略；(iii)水力结构及碳平衡对兰属附生植物在干旱胁迫中存活的影响，进而阐明兰属附生植物的水分适应特征，为种质资源的保护利用提供科学依据。发表SCI论文6篇，培养研究生2名。

兰属是重要的观赏植物，近年来受到肆意采挖和生境破坏的威胁。兰属植物有附生和地生两种生活型，附生生境的水分供应相对受限。环境适应性的认识对物种资源的保护与利用具有重要意义，但相关研究匮乏。项目从形态结构、生理和蛋白质组学角度研究了兰属附生种和地生种的水分适应策略。研究内容包括兰属植物利用的水分来源、兰属植物对自然水分变化的生理响应、兰属植物响应干旱胁迫的机制、叶片形态结构对水分适应的影响、墨兰与西藏虎头兰假鳞茎在干旱胁迫中的响应差异。取得的主要结果包括：（1）兰属附生种利用更高比例的雾水，而地生种利用更高比例的土壤水，雾水是两种生活型兰花旱季的重要水源。（2）地生型墨兰采取的是“补救策略”，附生型西藏虎头兰利用的是“预防策略”。附生种叶片比地生种的饱和含水量更高，失水更慢，假鳞茎储水细胞更大。附生种更强的组织储水和耐失水能力延长光合作用的维持时间，提高了耐旱性。西藏虎头兰在干旱时通过环式电子激发来提高增强光保护，墨兰则通过提高抗氧化酶活性增强来应对干旱胁迫。铁氧化还原蛋白-NADP 还原酶上调证实了西藏虎头兰能通过环式电子传递激发增强光保护。（3）糖含量在自然干旱条件下和控制实验中均无降低，说明兰属植物在干旱胁迫时能有效地维持碳平衡，水力结构失调可能是影响其在干旱胁迫下存活的主要因素。（4）附生种与地生种的水分适应策略明显分异。更高的组织储水能力和耐失水性使附生种在干旱胁迫时可维持更长时间的水分平衡和光合作用时间，应对水分供应的不足，从而成功地占据树冠生境。项目发表SCI论文11篇，培养研究生4名。研究结果为认识兰科植物的生态适应、物种资源的保护利用奠定了重要基础。