Partial mycoheterotrophy in orchids

在菌根共生中，植物将光合作用产生的碳水化合物交换为真菌从土壤中获得的矿物质营养。这种互利互惠的安排已经被几百种缺乏光合作用能力的菌根植物物种所破坏。这种真菌异养营养的最多的例子是在兰科植物中发现的。虽然不含叶绿素的兰花物种长期以来被认为是真菌异养的，但直到最近，绿色兰花才被认为是完全自养的。最近的数据的C和N的稳定同位素丰度与分子生态学鉴定的真菌在兰花根，但是，提供的证据表明，至少有一些的绿色兰花（i）获得的C和N部分在真菌的成本和（ii）开关真菌的合作伙伴对菌根与外生菌根真菌的林木。该项目旨在加深我们的知识（i）通过包括更广泛的兰花栖息地和分类群体，以及（ii）在这种迄今未知的植物营养模式发生的环境条件（光照气候，氮供应作为限制因素）下，这种部分真菌异养营养在陆生兰花中的分布。

In the mycorrhizal symbiosis, plants exchange carbohydrates from photosynthesis for mineral nutrients acquired by fungi from the soil. This mutualistic arrangement has been subverted by a few hundreds of mycorrhizal plant species that lack the ability to photosynthesize. The most numerous examples of this mycoheterotrophic nutrition are found among the orchid family. Although chlorophyll free orchid species are known since long to be mycoheterotrophic, green orchids have been thought until recently to be fully autotrophic. Recent data of C and N stable isotope abundances together with molecular ecological identification of fungi in orchid roots, however, provide evidence that at least some of the green orchids (i) gain C and N partially at the cost of fungi and (ii) switch the fungal partner towards mycorrhizas with ectomycorrhizal fungi of forest trees. This project aims to deepen our knowledge (i) on the distribution of this partially mycoheterotrophic nutrition among terrestrial orchids by including a broader spectrum of orchid habitats and taxonomic groups and (ii) on the environmental conditions (light climate, nitrogen availability as limiting factors) under which this hitherto unknown plant nutritional mode occurs.