Alghamdi Sameera A
Department of Biological Sciences, Faculty of Sciences, King Abdulaziz University, P.O. Box 42805, Jeddah 21551, Saudi Arabia.
Saudi J Biol Sci. 2019 Mar;26(3):495-502. doi: 10.1016/j.sjbs.2017.10.021. Epub 2017 Oct 13.
Epiphytes constitute over 70% of orchid diversity, but little is known about the functioning of their mycorrhizal associations. Terrestrial orchid seeds germinate symbiotically in soil and leaf litter, whereas epiphytic orchids may be exposed to relatively high light levels from an early stage of development and often produce green seeds. This suggests that seedlings of the two groups of orchids may differ in their responses to light and requirements for mycorrhiza-supplied carbon. The interactive effects of light, exogenous carbon and mycorrhizal status on germination and growth were investigated using axenic agar microcosms for one tropical epiphyte and three geophytic orchid species The geophytic species strongly depended on their mycorrhiza for growth and this could not be substituted by exogenous sucrose, whereas the epiphytic species achieved 95% of the mycorrhizal seedling volume when supplied with exogenous sucrose in the dark. Mycorrhiza status strongly interacted with light exposure, enabling germination. Light inhibited or severely reduced growth, especially for the terrestrial orchids in the absence of mycorrhiza. For the first time, this study showed the parallel ecological importance of mycorrhizal fungi in overcoming light inhibition of seed germination and growth in both terrestrial and epiphytic orchids.
附生植物占兰花多样性的70%以上，但人们对其菌根共生关系的功能了解甚少。地生兰花种子在土壤和落叶层中通过共生方式萌发，而附生兰花在发育早期可能会受到相对较高的光照水平，并且通常产生绿色种子。这表明这两类兰花的幼苗对光的反应以及对菌根提供的碳的需求可能存在差异。利用无菌琼脂微宇宙对一种热带附生兰花和三种地生兰花进行了研究，以探讨光、外源碳和菌根状态对萌发和生长的交互作用。地生兰花种类强烈依赖其菌根进行生长，而这不能被外源蔗糖所替代，而附生兰花种类在黑暗中供应外源蔗糖时，其菌根幼苗体积达到了95%。菌根状态与光照暴露强烈相互作用，促进萌发。光照抑制或严重降低生长，尤其是对于没有菌根的地生兰花。本研究首次表明，菌根真菌在克服光照对陆地和附生兰花种子萌发和生长的抑制方面具有同等的生态重要性。
