Abstract：
OBJECTIVE: The earliest diverging orchid lineage Apostasioideae consists only of two genera: Apostasia and Neuwiedia. Previous report of Apostasia nipponica indicated a symbiotic association with an ectomycorrhiza-forming Ceratobasidiaceae clade and partial utilization of fungal carbon during the adult stage. However, the trophic strategy of Neuwiedia throughout its development remains unidentified. To further improve our understanding of mycoheterotrophy in the Apostasioideae, this study focused on Neuwiedia malipoensis examining both the mycorrhizal association and the physiological ecology of this orchid species across various development stages.
METHODS: We identified the major mycorrhizal fungi of N. malipoensis protocorm, leafy seedling and adult stages using molecular barcoding. To reveal nutritional resources utilized by N. malipoensis, we compared stable isotope natural abundance (δ13C, δ15N, δ2H, δ18O) of different developmental stages to autotrophic reference plants.
RESULTS: Protocorms exhibited an association with saprotrophic Ceratobasidiaceae rather than ectomycorrhiza-forming Ceratobasidiaceae and 13C signature was characteristic of their fully mycoheterotrophic nutrition.Seedlings and adults predominantly associated with saprotrophic fungi belonging to the Tulasnellaceae. While 13C and 2H stable isotope data revealed partial mycoheterotrophy of seedlings, it is unclear to what extent the fungal carbon supply is reduced in adult N. malipoensis. However, the 15N enrichment of mature N. malipoensis suggests partially mycoheterotrophic nutrition.Our data indicated a transition in mycorrhizal partners during ontogenetic development with decreasing dependency of N. malipoensis on fungal nitrogen and carbon.
CONCLUSIONS: The divergence in mycorrhizal partners between N. malipoensis and A. nipponica indicates different resource acquisition strategies and allows for various habitat options in the earliest diverging orchid lineage Apostasioideae. While A. nipponica relies on the heterotrophic C gain from its ectomycorrhizal fungal partner and thus on forest habitats, N. malipoensis rather relies on own photosynthetic C gain as adult allowing it to establish in habitats as widely distributed as those where Rhizoctonia fungi occur.
METHODS: We identified the major mycorrhizal fungi of N. malipoensis protocorm, leafy seedling and adult stages using molecular barcoding. To reveal nutritional resources utilized by N. malipoensis, we compared stable isotope natural abundance (δ13C, δ15N, δ2H, δ18O) of different developmental stages to autotrophic reference plants.
RESULTS: Protocorms exhibited an association with saprotrophic Ceratobasidiaceae rather than ectomycorrhiza-forming Ceratobasidiaceae and 13C signature was characteristic of their fully mycoheterotrophic nutrition.Seedlings and adults predominantly associated with saprotrophic fungi belonging to the Tulasnellaceae. While 13C and 2H stable isotope data revealed partial mycoheterotrophy of seedlings, it is unclear to what extent the fungal carbon supply is reduced in adult N. malipoensis. However, the 15N enrichment of mature N. malipoensis suggests partially mycoheterotrophic nutrition.Our data indicated a transition in mycorrhizal partners during ontogenetic development with decreasing dependency of N. malipoensis on fungal nitrogen and carbon.
CONCLUSIONS: The divergence in mycorrhizal partners between N. malipoensis and A. nipponica indicates different resource acquisition strategies and allows for various habitat options in the earliest diverging orchid lineage Apostasioideae. While A. nipponica relies on the heterotrophic C gain from its ectomycorrhizal fungal partner and thus on forest habitats, N. malipoensis rather relies on own photosynthetic C gain as adult allowing it to establish in habitats as widely distributed as those where Rhizoctonia fungi occur.
摘要：
目的：最早的兰花谱系异位子科仅由两个属组成：异位子和Neuwiedia。先前的日本无位症报告表明，在成年阶段，与形成外生菌根的Ceratobasidiaceae进化枝和部分利用真菌碳的共生关系。然而,Neuwiedia在其整个发展过程中的营养策略仍未确定。为了进一步提高我们对Apostasioideae中的杂种病的认识，这项研究的重点是Neuwiediamalipoensis，研究了该兰花物种在各个发育阶段的菌根关联和生理生态。
方法：我们确定了马氏原球茎的主要菌根真菌，使用分子条形码的多叶幼苗和成虫阶段。为了揭示马立马利用的营养资源，我们比较了稳定同位素自然丰度(δ13C，δ15N,δ2H,自养参考植物不同发育阶段的δ18O）。
结果：原球茎表现出与腐生角果科的关联，而不是外生菌根形成的角果科，13C特征是其完全异养营养的特征。幼苗和成虫主要与属于Tulasnellaceae的腐生真菌有关。虽然13C和2H稳定同位素数据显示幼苗部分杂菌萎缩，目前尚不清楚成虫N.malipoensis的真菌碳供应减少到什么程度。然而,成熟N.malipoensis的15N富集表明部分真菌异养营养。我们的数据表明，在个体发育过程中，菌根伴侣发生了转变，而马氏N.malipoensis对真菌氮和碳的依赖性降低。
结论：马拉伯氏菌和日本A.之间菌根伴侣的差异表明了不同的资源获取策略，并允许在最早发散的兰花谱系Aposasioideae中进行各种栖息地选择。虽然日本扁桃依赖于其外生菌根真菌伴侣的异养C增益，因此依赖于森林栖息地，N.malipoensis相当依赖自身的光合C增益作为成年人，使其能够在与发生根瘤菌真菌一样广泛分布的栖息地中建立。
方法：我们确定了马氏原球茎的主要菌根真菌，使用分子条形码的多叶幼苗和成虫阶段。为了揭示马立马利用的营养资源，我们比较了稳定同位素自然丰度(δ13C，δ15N,δ2H,自养参考植物不同发育阶段的δ18O）。
结果：原球茎表现出与腐生角果科的关联，而不是外生菌根形成的角果科，13C特征是其完全异养营养的特征。幼苗和成虫主要与属于Tulasnellaceae的腐生真菌有关。虽然13C和2H稳定同位素数据显示幼苗部分杂菌萎缩，目前尚不清楚成虫N.malipoensis的真菌碳供应减少到什么程度。然而,成熟N.malipoensis的15N富集表明部分真菌异养营养。我们的数据表明，在个体发育过程中，菌根伴侣发生了转变，而马氏N.malipoensis对真菌氮和碳的依赖性降低。
结论：马拉伯氏菌和日本A.之间菌根伴侣的差异表明了不同的资源获取策略，并允许在最早发散的兰花谱系Aposasioideae中进行各种栖息地选择。虽然日本扁桃依赖于其外生菌根真菌伴侣的异养C增益，因此依赖于森林栖息地，N.malipoensis相当依赖自身的光合C增益作为成年人，使其能够在与发生根瘤菌真菌一样广泛分布的栖息地中建立。
