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.
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。