Faculty of Agriculture, Saga University, Saga, Japan.
Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany.
Mol Ecol. 2018 Mar;27(5):1324-1337. doi: 10.1111/mec.14524. Epub 2018 Mar 6.
The climbing orchid Erythrorchis altissima is the largest mycoheterotroph in the world. Although previous in vitro work suggests that E. altissima has a unique symbiosis with wood-decaying fungi, little is known about how this giant orchid meets its carbon and nutrient demands exclusively via mycorrhizal fungi. In this study, the mycorrhizal fungi of E. altissima were molecularly identified using root samples from 26 individuals. Furthermore, in vitro symbiotic germination with five fungi and stable isotope compositions in five E. altissima at one site were examined. In total, 37 fungal operational taxonomic units (OTUs) belonging to nine orders in Basidiomycota were identified from the orchid roots. Most of the fungal OTUs were wood-decaying fungi, but underground roots had ectomycorrhizal Russula. Two fungal isolates from mycorrhizal roots induced seed germination and subsequent seedling development in vitro. Measurement of carbon and nitrogen stable isotope abundances revealed that E. altissima is a full mycoheterotroph whose carbon originates mainly from wood-decaying fungi. All of the results show that E. altissima is associated with a wide range of wood- and soil-inhabiting fungi, the majority of which are wood-decaying taxa. This generalist association enables E. altissima to access a large carbon pool in woody debris and has been key to the evolution of such a large mycoheterotroph.
攀援石豆兰 Erythrorchis altissima 是世界上最大的菌根异养植物。尽管之前的体外研究表明，E. altissima 与木质腐朽真菌存在独特的共生关系，但对于这种巨型兰花如何仅通过菌根真菌来满足其碳和营养需求知之甚少。在这项研究中，使用来自 26 个个体的根样本，对 E. altissima 的菌根真菌进行了分子鉴定。此外，还对五个真菌的体外共生萌发以及一个地点的五个 E. altissima 的稳定同位素组成进行了研究。总共从兰花根中鉴定出了 37 个属于担子菌门九个目、属于 37 个菌根真菌操作分类单位（OTU）的真菌。大多数真菌 OTU 是木质腐朽真菌，但地下根系有外生菌根 Russula。从菌根根中分离出的两个真菌分离物在体外诱导种子萌发和随后的幼苗发育。碳和氮稳定同位素丰度的测量表明，E. altissima 是一种完全菌根异养植物，其碳主要来源于木质腐朽真菌。所有结果均表明，E. altissima 与广泛存在于木质部和土壤中的真菌有关，其中大多数为木质腐朽真菌。这种广义的关联使 E. altissima 能够利用木质残体中的大量碳库，这是形成如此大型菌根异养植物的关键。
