Variation in mycorrhizal communities and the level of mycoheterotrophy in grassland and Forest populations of Neottia ovata (Orchidaceae)

Orchid mycorrhiza forms unique symbiotic associations between members of the Orchidaceae and multiple ecological guilds of fungi. Because orchids associate with a wide variety of fungi with different ecological functions, they represent an ideal study system to address fundamental questions about the evolution and ecophysiology of mycorrhizal symbiosis. Although it is well established that shifts in mycorrhizal associations are linked to transitions in plant trophic mode, it remains unclear what ecological drivers promote these evolutionary changes. Here, we investigated mycorrhizal communities and isotope signatures across six populations of the terrestrial orchid Neottia ovata growing under contrasting light conditions in temperate Europe. We hypothesized that plants growing in forests would associate with different mycorrhizal fungi than plants occurring in grasslands and that the limited light availability in forests leads to a higher contribution of fungi to the carbon budget of orchids. Our results showed that N. ovata predominantly associated with rhizoctonia fungi of the family Serendipitaceae in both habitats, but plants in forests also recruited ectomycorrhizal fungi. Root communities highly resembled soil communities and variation in root communities was significantly related to habitat type and edaphic factors. In contrast, isotope signatures (13C, 15N, 2H and 18O) and N concentration showed no significant relationship with habitat type. In addition, both 13C and 2H were not significantly correlated to habitat's light availability. Although it has been suggested that the presence of a wide variety of ectomycorrhizal fungi in root communities of orchids can serve as a precursor for evolutionary shifts to partial mycoheterotrophy (mixotrophy), the presence or absence of ectomycorrhizal fungi did not substantially influence the isotope signatures of N. ovata. These results indicate that rhizoctonia fungi played the major functional role in C and nutrient supply and that ectomycorrhizal fungi did not substantially contribute to the carbon budget of the plants. Read the free Plain Language Summary for this article on the Journal blog. 摘要 兰科植物与菌根真菌形成的一种独特的菌根类型—兰花菌根。因为兰科植物可与多种不同生态型的菌根真菌共生，兰花菌根是研究菌根真菌进化和生理生态等基础科学问题的理想研究体系。尽管菌群变化和植物营养型转变的相关性已为学界熟知，但是驱动这些变化的生态因子仍不明了。. 本研究以地生兰科植物对叶兰为材料，调查其真菌群落和叶片同位素在温带欧洲六种不同生境中的特征。我们假设对叶兰在森林和草原生境中招募不同的真菌群落，低光照的森林生境驱使对叶兰通过菌根真菌获取更多的有机碳。. 我们发现，不同生境中的对叶兰都与典型的兰花真菌—肉丝耳科(Serendipitaceae)共生，但是森林中对叶兰额外招募了更多的外生菌根菌。植物根的菌根菌群与同一生境中的土壤