亚热带森林附生植物叶片气孔特征及其可塑性对光照变化的响应

Response of stomatal characteristics and its plasticity to light change in leaves of six epiphytes in subtropical forests

关键词:  植物生理生态, 哀牢山, 林冠, 光环境改变, 附生植物, 气孔特性, 表型可塑性

Key words:  plant physioecology, Ailao Mountains, canopy, light change, epiphyte, stomatal characteristic, phenotype plasticity

摘要:

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。光照被认为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。然而,由于接近林冠和规范性采样的限制,附生植物与光照的关系仍亟待阐述。为揭示附生植物对光强变化的响应和适应策略,该研究以亚热带常绿阔叶林6种附生植物(林冠层木本:鼠李叶花楸、毛棉杜鹃; 林冠层草本:狭瓣贝母兰、毛唇独蒜兰; 树干区草本:点花黄精、距药姜)为对象,对其在4个光处理梯度下生长的叶片气孔特征及其可塑性进行了对比分析。结果表明:(1)2种附生小乔木的气孔面积(SA)、气孔密度(SD)、潜在气孔导度指数(PCI)和表皮细胞密度(ECD)均对光强改变显著响应。2种附生兰科植物的SA最大,而SD最小; 附生乔木叶片SD和ECD的光响应趋势与陆生植物更相似,而附生草本则出现种间差异。(2)6种附生植物的气孔、表皮细胞特性及其表型可塑性,在草本-木本、常绿-落叶植物、林冠-树干区之间,均无明显差别。(3)附生植物气孔特性和表皮细胞平均可塑性指数均低于陆生植物。综上结果表明,亚热带常绿阔叶林中附生植物对于光环境变化的适应性相对较弱。不同的附生植物可以通过不同程度地增加叶片SD和ECD来适应高光强生境,并通过对SD和SA的双重调节以增大潜在光合能力从而应对低光胁迫。

Abstract:

Epiphytes, which grow non-parasitically upon other plants, comprise one of the most diverse and vulnerable groups in subtropical and tropical forests. Light can promote the evolutionary transition of plants from terrestrial to epiphytic life-forms and determine the growth and distribution of epiphytes. Nevertheless, the research on the relation between epiphyte growth and light stress has been plagued by some technical problems such as direct canopy access and systematic sampling. In order to explore the adaptation strategies and mechanisms of epiphytes to light change, six vascular epiphytes, including two canopy trees Sorbus rhamnoides and Rhododendron moulmainense, two canopy herbs Coelogyne punctulata and Pleione hookeriana, two trunk herbs Polygonatum punctatum and Cautleya gracilis, were surveyed to study the stomatal characteristics and plasticity in leaves of vascular epiphytes and their responses to light change in evergreen broad-leaved forests in the Ailao Mountains of Yunnan Province. The results were as follows:(1)The stomatal area(SA), stomatal density(SD), potential stomatal conductance index(PCI)and epidermal cell density(ECD)of the two canopy epiphytic trees responded significantly to light change. The canopy epiphytic herbs had the largest SA and the smallest SD among all the studied epiphytes. The response of the SD and ECD of epiphytic trees to light change was consistent with those of terrestrial plants, while epiphytic herbs showed interspecific variations.(2)The stomatal and epidermal cell characteristics, and phenotype plasticity of epiphytes showed no significant differences between herbs and trees, evergreen and deciduous plants, and canopy and trunk epiphytes.(3)Their plasticity indexes of stomatal and epidermal cell characteristics were lower than those of terrestrial plants. Our results indicate that epiphytes have relatively weak adaptability to light change in subtropical forests. Epiphytes are able to adapt to high light intensity by increasing SD and ECD with different degrees, and to cope with low light stress by increasing potential photosynthetic capacity with trade-offs between SD and SA.