Kings Park Science, Biodiversity and Conservation Science, Department of Biodiversity, Conservation and Attractions, 2 Kattidj Close, Kings Park, WA, Australia.
School of Biological Sciences, The University of Western Australia, Crawley, Perth, WA, Australia.
Ann Bot. 2022 May 12;129(6):669-678. doi: 10.1093/aob/mcac030.
Many terrestrial orchids have an obligate dependence on their mycorrhizal associations for nutrient acquisition, particularly during germination and early seedling growth. Though important in plant growth and development, phosphorus (P) nutrition studies in mixotrophic orchids have been limited to only a few orchid species and their fungal symbionts. For the first time, we demonstrate the role of a range of fungi in the acquisition and transport of inorganic P to four phylogenetically distinct green-leaved terrestrial orchid species (Diuris magnifica, Disa bracteata, Pterostylis sanguinea and Microtis media subsp. media) that naturally grow in P-impoverished soils.
Mycorrhizal P uptake and transfer to orchids was determined and visualized using agar microcosms with a diffusion barrier between P source (33P orthophosphate) and orchid seedlings, allowing extramatrical hyphae to reach the source.
Extramatrical hyphae of the studied orchid species were effective in capturing and transporting inorganic P into the plant. Following 7 d of exposure, between 0.5 % (D. bracteata) and 47 % (D. magnifica) of the P supplied was transported to the plants (at rates between 0.001 and 0.097 fmol h-1). This experimental approach was capable of distinguishing species based on their P-foraging efficiency, and highlighted the role that fungi play in P nutrition during early seedling development.
Our study shows that orchids occurring naturally on P-impoverished soils can obtain significant amounts of inorganic P from their mycorrhizal partners, and significantly more uptake of P supplied than previously shown in other green-leaved orchids. These results provide support for differences in mycorrhiza-mediated P acquisition between orchid species and fungal symbionts in green-leaved orchids at the seedling stage. The plant-fungus combinations of this study also provide evidence for plant-mediated niche differentiation occurring, with ecological implications in P-limited systems.
许多陆生兰花对其菌根共生体有专性依赖，以获取养分，尤其是在种子萌发和幼苗早期生长过程中。尽管磷（P）营养在植物生长和发育中很重要，但混合营养兰花的 P 营养研究仅限于少数兰花物种及其真菌共生体。我们首次证明了一系列真菌在获取和运输无机 P 方面的作用，供体为 33P 正磷酸盐，实验对象为四个在贫磷土壤中自然生长的、亲缘关系较远的绿叶陆生兰花物种（大距沼兰、棒距沼兰、血叶兰和中肋毛兰）。
采用琼脂微宇宙方法，在 P 源（33P 正磷酸盐）和兰花幼苗之间设置扩散屏障，以确定和可视化菌根对兰花的 P 吸收和转移，从而使外生菌根能够到达 P 源。
研究的兰花物种的外生菌根能够有效地捕获和将无机 P 运输到植物体内。暴露 7 天后，供体中的 0.5%（棒距沼兰）至 47%（大距沼兰）的 P 被转运到植物体内（转运速率为 0.001 至 0.097 fmol h-1）。这种实验方法能够根据物种的 P 觅食效率来区分物种，并突出了真菌在幼苗早期发育过程中在 P 营养方面的作用。
我们的研究表明，在贫磷土壤中自然生长的兰花可以从其菌根伙伴中获得大量的无机 P，并且对所供应 P 的吸收量明显高于其他绿叶兰花中所显示的吸收量。这些结果为兰花物种与绿叶兰花真菌共生体之间在菌根介导的 P 获取方面的差异提供了支持。本研究中的植物-真菌组合也为植物介导的生态位分化提供了证据，这在 P 限制系统中具有生态意义。
