Data from: Limitations on orchid recruitment: not a simple picture

Mycorrhizal fungi have substantial potential to influence plant distribution, especially in specialized orchids and mycoheterotrophic plants. However, little is known about environmental factors that influence the distribution of mycorrhizal fungi. Previous studies using seed packets have been unable to distinguish whether germination patterns resulted from the distribution of appropriate edaphic conditions or the distribution of host fungi, as these cannot be separated using seed packets alone. We used a combination of organic amendments, seed packets, and molecular assessment of soil fungi required by three terrestrial orchid species to separate direct and indirect effects of fungi and environmental conditions on both seed germination and subsequent protocorm development. We found that locations with abundant mycorrhizal fungi were most likely to support seed germination and greater growth for all three orchids. Organic amendments affected germination primarily by affecting the abundance of appropriate mycorrhizal fungi. However, fungi associated with the three orchid species were affected differently by the organic amendments and by forest successional stage. The results of this study help contextualize the importance of fungal distribution and abundance to the population dynamics of plants with specific mycorrhizal requirements. Such phenomena may also be important for plants with more general mycorrhizal associations.

菌根真菌（mycorrhizal fungi）对植物分布具有显著调控潜力，尤其对于特化兰科植物与菌异养植物（mycoheterotrophic plants）而言。然而目前学界对影响菌根真菌分布的环境因子仍知之甚少。既往采用种子包（seed packets）开展的研究无法区分，种子萌发模式究竟是由适宜土壤生境条件还是宿主真菌分布所导致，因为仅依靠种子包实验无法将二者有效分离。本研究结合有机改良剂（organic amendments）、种子包实验与三种陆生兰科植物所需土壤真菌的分子检测手段，旨在厘清真菌与环境条件对种子萌发及后续原球茎（protocorm）发育的直接与间接效应。研究发现，菌根真菌丰度较高的生境，最利于三种兰科植物的种子萌发与植株生长。有机改良剂主要通过调控适宜菌根真菌的丰度来影响种子萌发，但针对三种兰科植物的共生真菌而言，有机改良剂与森林演替阶段对其的影响存在显著差异。本研究结果有助于明确真菌分布与丰度对具有特定菌根依赖特性植物的种群动态的重要意义。此类现象对于具备广谱菌根关联模式的植物而言，同样具有重要研究价值。