Understanding the functional basis of orchid mycorrhiza - associations

兰花的许多品种是所有植物中最稀有的，但由于缺乏对其基本生物学的基本了解，保护工作变得更加困难。兰花是最新和发展最快的植物之一，是世界上最大的植物家族，拥有超过20,000种。兰花大量的种子产量促进了兰花的快速多样化，一株植物每年通常释放超过25,000颗种子。这种多产的繁殖只有通过最小化种子大小才有可能，而兰花的种子是如此的小，以至于它们没有足够的储备来允许自己发芽和建立。相反，这些植物与土壤真菌形成了一种共生联盟（共同生活），以提供从种子开始生长所需的资源。幼苗发育的第一阶段是形成一个最初无叶的植物，称为原球茎，其中生长所需的所有碳和矿物质营养都由其真菌伴侣提供。大多数其他植物也与土壤真菌（称为菌根，字面意思是“真菌根”）形成共生关系，但在大多数情况下，植物通过光合作用将碳固定给真菌，以换取从土壤中吸收的矿物质营养。这是一种互利共生的关系，双方都从关系中获益。兰花和真菌共生的不寻常之处在于，真菌为幼苗提供营养和碳，但对自己没有任何明显的好处。为什么真菌会允许自己明显地以这种方式寄生？我最近的研究揭示了兰花和真菌之间的相互作用。利用富含这些元素特定同位素的碳、氮和磷源，我已经能够解开围绕这种不寻常的共生关系的一些谜团，第一次回答了两个关键问题；表明真菌可以，在一个物种中，从这种共生关系中受益，并且成年兰花继续从这种共生关系中受益。尽管在一种兰花上取得了重大突破，但我们还不知道其他绿色兰花是否也有这种行为，碳和营养物质是如何在植物和真菌之间转移的，以及是否能够从真菌中获得碳，使得一些成年兰花能够在弱光条件下生活，在这种条件下，它们无法将足够的碳固定成糖来满足它们的需要，并有效地作为真菌的寄生虫生活。该项目旨在解决这些关键领域，这些领域对兰花-真菌共生的基本生物学缺乏根本的了解。

Many species of orchid are amongst the rarest of all plants yet conservation efforts are made more difficult by a fundamental lack of knowledge into their basic biology. Orchids are amongst the newest and most rapidly evolving plants, comprising the largest plant family with over 20,000 species worldwide. Rapid diversification of orchids is facilitated by their vast seed production, a single plant typically releasing over 25,000 seeds per year. Such prolific reproduction is only possible by minimising seed size, and orchid seeds are so reduced that they contain insufficient reserves to permit germination and establishment on their own. Instead, these plants have forged a symbiotic alliance (living together) with soil fungi to provide the resources required to establish from seed. The first stage of seedling development is the formation of an initially leafless plantlet called a protocorm in which all of the carbon and mineral nutrients required to grow are supplied by its fungus partner. Most other plants also form symbiotic associations with soil fungi (termed mycorrhizas, literally meaning 'fungus root'), but in the majority of these cases the plant supplies carbon, which it has fixed through photosynthesis, to the fungus in return for mineral nutrients taken up from soil. This is a mutualistic symbiosis where both partners derive a benefit the relationship. What is unusual about the orchid-fungal symbiosis is that the fungus supplies both nutrients and carbon to the young plants without any obvious benefit to itself. Why does the fungus allow itself to be apparently parasitised in this way? My recent studies have shed light on the interactions between orchid and fungus. Using carbon, nitrogen and phosphorus sources enriched with specific isotopes of these elements, I have been able to unravel some of the mysteries surrounding this unusual symbiosis, answering two key questions for the first time; showing that the fungus can, in one species, benefit from this symbiosis and that the adult orchid continues to benefit from this symbiosis. Despite this major breakthrough with one species of orchid, we do not yet know whether any other green orchids behave in this way, how the carbon and nutrients are transferred between plant and fungus and whether being able to acquire carbon from a fungus has enabled some adult orchids to live in low light conditions where they are unable to fix enough carbon into sugars to meet their needs and effectively live as a parasite on the fungus. This project aims to address these key areas where there is a fundamental lack of understanding of the basic biology of orchid-fungus symbioses.