光照调控附生植物空间分布格局的生理生态学机制研究——基于受损常绿阔叶林

Epiphytes, which grow non-parasitically upon other plants, comprise one of the most diverse and vulnerable groups in subtropical and tropical forests. They improve the structural complexity of forests and play a vital role in the biodiversity maintenance, environmental monitoring, water and nutrient cycling in various forest ecosystems. Light can promote the evolutionary transition of plants from terrestrial to epiphytic life-forms and determine the growth and distribution of epiphytes. In order to obtain adequate light for growing and surviving, epiphytes have to suffer from severe water shortage, low availability of nutrients and high risk of falling from hosts. Nevertheless, the relation between epiphyte growth and light stress and the mechanism of light in determining the spatial distribution pattern of epiphytes have been plagued by some technical problems such as direct canopy access and systematic sampling. Moreover, the majority of available studies dealing with the ecophysiology of epiphytes have been limited to laboratory and greenhouse, however, some questions can only be answered by in-situ work and should also be conducted to confirm laboratory studies. In this project, we will conduct field controlled and in-situ experiments to characterize the leaf morphological and physiological traits of vascular epiphytes and their responses to different light regimes such as high light, weak light, light change and lightflecks in the snow-damaged primary evergreen broad-leaved forests in the Ailao Mountains in Yunnan Province. Epiphyte species and individuals will be studied in six vertical light zones through in-situ experiments using canopy crane. In addition, a number of samplings of vascular epiphytes, which have been collected from snow-fallen trees from April to August in 2016, will be cultivated in four light gradient plots for 1-2 years and then used for controlled experiments. In these experiments, the morphological traits, anatomical features, nutrient concentrations, δ13C content, photosynthetic performances, fluorescence parameters and chlorophyll concentrations of epiphyte leaves will be quantitated by using stable isotope analysis, scanning electron microscope, photosynthesis analysis and chlorophyll fluorescence techniques, and so on. Meanwhile, we will compare the pathway of photosynthetic carbon assimilation, water use efficiency, carbohydrate production rate, photosynthetic nitrogen-use and phosphorus-use efficiencies, nitrogen cost of photosynthetic components and leaf construction cost for epiphytes among different light conditions. The objective of this study is to address the adaptive strategies of epiphytes to light stress and the ecophysiological mechanism of light in determining the spatial distribution pattern of epiphytes in subtropical evergreen broad-leaved forests. Our information can provide scientific basis for biodiversity maintenance, vulnerable species conservation and forest resource management under global changes.

附生植物是热带亚热带森林生态系统中物种多样性极高且极其脆弱敏感的生物类群之一，在群落结构复杂性提升、生物多样性维系、环境监测、水文和营养循环等方面具有重要作用。光照是促进附生植物由陆生类群演化而来并决定其生长和分布的关键因素。但由于林冠访问和规范采样等技术性问题的限制，附生植物与光照的关系以及光照调控附生植物空间分布的生理机制尚不明确。本项目以云南哀牢山因雪灾受损的原生常绿阔叶林附生维管植物为对象，利用林冠塔吊系统开展原位实验，同时以趁雪灾契机采集自倒木的附生维管植物为材料开展野外控制实验，采用稳定同位素、扫描电子显微镜、光合系统分析和叶绿素荧光等技术，研究附生植物叶片形态和生理性状对高光、低光、光环境转换以及光斑的响应过程和特征，阐述附生维管植物应对光胁迫的适应策略，揭示光照调控附生植物空间分布格局的生理生态学机制，为全球变化背景下生物多样性维系、脆弱物种保护和森林资源管理提供科学依据。

附生植物是热带亚热带森林系统中物种多样性极高且具有重要功能的脆弱生物类群。由于林冠访问和规范采样等技术瓶颈，光照调控附生植物空间分布格局的生理机制仍有待阐明。本项目以云南哀牢山雪灾受损的原生常绿阔叶林附生维管植物为对象，利用林冠塔吊系统开展原位实验，结合采集雪后倒木上的附生植物开展控制实验，探讨了附生植物个体生长和分布对光照变化的适应策略，并建立了附生植物长期实验平台。研究发现，附生植物在原生林内垂直分层显著，林冠类群随分布高度降低个体显著减少，树干类群与之相反。小气候因子如光照、温度、湿度和风速等均对其垂直分布具有显著影响；光照是最主要的调控因子，但对林冠和树干类群的影响具有明显差异。附生植物的垂直分布模式也被其物种、个体生理特性和生境适应策略共同影响。水分充足条件下，附生植物光合潜能无明显种间差异，但树干类群具有更广的光照分布范围。控光实验表明，附生植物普遍存在高光胁迫现象；其累积叶片有机质的最适合光照约为60%全光照。结合主成分分析发现，高光环境下，附生植物最大净光合速率和叶片干物质含量普遍增大，比叶面积减小；低光环境下，附生植物叶片相对含水量增大，胞间CO2浓度和气孔导度降低。极端光胁迫会破环其叶片光系统，抑制光合作用，造成附生植物个体死亡；但低光胁迫可能是附生植物物种和个体在原生林内垂直下移的关键制约因素。总体而言，典型附生维管植物的表型可塑性低于陆生植物类群，环境变化适应性较弱，耐受性更差，生态幅更窄；但半附生植物类群表现出极高的种群恢复能力。本项目的实施，为揭示光照调控附生植物空间分布格局的生理生态学机制做出贡献，为全球变化背景下生物多样性维系、脆弱生物类群保护和森林资源管理提供科学依据。