青藏高原水生植物对极端环境的适应策略—来自叶功能性状的证据

Plants functional traits are defined as morphological, physiological and phenological traits which impact fitness via their effects on plants growth, reproduction and survival, and always used as the predictors of organismal performance. Such traits bridge the environments, individuals and higher level of organizations, and capture the species distribution variations along environmental gradients. Exploring the effects of environmental variations on functional traits could help us to understand the mechanisms for species survival and distribution. Studies on the relationships between environments and plant functional traits are well documented in terrestrial ecosystems. However, aquatic macrophytes are rarely referred in such researches. Tibetan Plateau, with average altitude achieving 4000 m, is the highest plateau and is named "the Third Pole" in the world. Alpine climate in Tibetan Plateau is characterized by low temperature, strong wind and intense radiation. In this study, based on this special geographical unit, we selected aquatic macrophytes as our target species, measured the functional traits, and clarified their geographical patterns and the relationships between the functional traits and environmental factors. The functional traits in this study included C:N:P stoichiometry, leaf area, leaf thickness, leaf density, leaf mass per area and leaf δ13C value. Firstly, we investigated aquatic habitats and collected specimens of all aquatic macrophytes species. The investigations were carried out in three scales: the whole plateau scale, drainage basin scale of a river, lake or marsh, and smaller scale of a stream or a lake. Then, we collected samples of aquatic macrophytes, water and substrate, to measure each functional traits of plants mentioned above and chemical elements of water and substrate. After laboratory measurements, we analyzed the effects of environmental factors (including climate and water quality) on plants functional traits. Finally, we identified the differences of functional traits among four life-forms of aquatic macrophytes and terrestrial plants along environmental gradients. Such analysis could enhance our knowledge to understand the different mechanisms of plants adaptive strategies between aquatic and terrestrial ecosystems. Additional, this study could provide research basis for further studies on plants survival, fitness and evolution of aquatic macrophytes in such harsh environments of Tibetan Plateau.

功能性状是植物在长期进化过程中发展出的适应其生存环境的特征，定量描述了植物的结构和功能，反映了植物的适应策略。研究比较不同环境或不同物种之间的功能性状，对判断植物对环境的适应程度和解释物种的地理分布格局具有重要意义。本项目基于青藏高原这一特殊的气候和地理单元平台，以水生植物为研究对象，利用野外调查和实验室化学分析等方法，在系统分析青藏高原水生植物多样性的基础上，探讨其功能性状的地理格局及其与环境因素的关系，试图阐明这一格局的驱动因素，为解释水生植物在青藏高原的分布格局提供可能的证据；并通过与其他生态系统类型进行比较，找出不同植物功能群之间的趋同或分异机制。本项目的实施有助于加强对不同生态系统和不同植物类群地理分布格局的理解，为进一步分析水生植物在青藏高原特殊生境下的生存、适应和进化规律奠定基础。

功能性状是定量描述植物结构和功能的特征指标，可以反映植物的适应策略。研究比较不同环境或不同物种之间的功能性状，对判断植物对环境的适应程度和解释物种的地理分布格局具有重要意义。本项目基于青藏高原这一特殊的气候和地理单元平台，以水生植物为研究对象，主要研究内容包括：①青藏高原不同水生生境进行标本采集和群落调查；②系统采集水生植物材料样品和水体及土壤基质样品，利用实验室分析方法测定样品的叶面积、比叶质量、叶密度、叶厚度、C:N:P 元素含量和δ13C 值等叶功能性状；③比较四种生活型植物叶功能性状地理分布格局的不同，结合环境因子探讨形成水生植物叶功能性状地理分布格局的限制因素。经过项目三年的实施，在青藏高原不同水体生境中采集标本12000余份，调查群落样方2000余个；调查不同水体450余处，采集水生植物体样品2000余个，水体及土壤基质样品各450余个；分析了植物功能性状中C:N:P元素含量及其比值、植物干重热值、灰分和建成消耗的环境和地理格局，比较了不同生活型植物之间的差异，并利用温度、水体理化参数等环境因子分析了其地理格局的限制因子。结果显示，青藏高原水生植物N、P元素含量显著高于低海拔地区和全球平均水平，且随温度降低而升高，表明该地区水生植物通过积累较高浓度的N、P元素以抵消低温所造成的酶促效率降低，以便在较短的生长季内快速完成生活史，这一结论对水生植物在青藏高原极端严酷生境下的适应进化具有指示意义；水体盐度是影响水生植物干重热值、灰分和建成消耗的主要环境因子，这一结论对青藏高原水生植物在该地区广泛存在的咸水和半咸水生境中的生存和能量积累具有指示意义。综上所述，本项目已有结果对解释水生植物对高原环境的适应和响应、以及未来气候变化背景下高原水生植物的演变趋势提供了来自元素和能量积累方面的证据。