Zahn Franziska E, Jiang Hong, Lee Yung-I, Gebauer Gerhard
Laboratory of Isotope Biogeochemistry, Bayreuth Center of Ecology and Environmental (BayCEER), University of Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany.
Yunnan Laboratory for Conservation of Rare, Endangered & Endemic Forest Plants, National Forestry and Grassland Administration, Yunnan Academy of Forestry and Grassland, Kunming 650201, Yunnan, People's Republic of China.
Ann Bot. 2024 Aug 22;134(3):511-520. doi: 10.1093/aob/mcae097.
The earliest-diverging orchid lineage, Apostasioideae, consists only of two genera: Apostasia and Neuwiedia. Previous reports 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.
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 abundances (δ13C, δ15N, δ2H, δ18O) of different developmental stages with those of autotrophic reference plants.
Protocorms exhibited an association with saprotrophic Ceratobasidiaceae rather than ectomycorrhiza-forming Ceratobasidiaceae and the 13C signature was characteristic of their fully mycoheterotrophic nutrition. Seedlings and adults were 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.
The divergence in mycorrhizal partners between N. malipoensis and A. nipponica indicates different resource acquisition strategies and allows various habitat options in the earliest-diverging orchid lineage, Apostasioideae. While A. nipponica relies on the heterotrophic carbon gain from its ectomycorrhizal fungal partner and thus on forest habitats, N. malipoensis rather relies on own photosynthetic carbon gain as an adult, allowing it to establish in habitats as widely distributed as those where Rhizoctonia fungi occur.
最早期分化的兰花谱系——拟兰亚科，仅由两个属组成：拟兰属和三蕊兰属。先前关于日本拟兰的报道表明其与形成外生菌根的角担菌科分支存在共生关系，且在成年阶段部分利用真菌碳源。然而，三蕊兰在其整个发育过程中的营养策略仍不明确。为了进一步加深我们对拟兰亚科中菌根异养现象的理解，本研究聚焦于麻栗坡三蕊兰，研究了该兰花物种在不同发育阶段的菌根关联及生理生态学。
我们使用分子条形码鉴定了麻栗坡三蕊兰原球茎、带叶幼苗和成株阶段的主要菌根真菌。为了揭示麻栗坡三蕊兰所利用的营养资源，我们将不同发育阶段的稳定同位素自然丰度（δ13C、δ15N、δ2H、δ18O）与自养参考植物的进行了比较。
原球茎与腐生的角担菌科相关联，而非形成外生菌根的角担菌科，其13C特征表明其完全菌根异养营养。幼苗和成株主要与属于丝核菌科的腐生真菌相关联。虽然13C和2H稳定同位素数据显示幼苗存在部分菌根异养现象，但尚不清楚成年麻栗坡三蕊兰中真菌碳供应减少的程度。然而，成熟麻栗坡三蕊兰的15N富集表明其存在部分菌根异养营养。我们的数据表明，在个体发育过程中菌根伙伴发生了转变，麻栗坡三蕊兰对真菌氮和碳的依赖性降低。
麻栗坡三蕊兰和日本拟兰在菌根伙伴上的差异表明了不同的资源获取策略，并使得最早期分化的兰花谱系——拟兰亚科能够选择多种栖息地。日本拟兰依赖于其外生菌根真菌伙伴获取异养碳，因此依赖森林栖息地，而麻栗坡三蕊兰成年后更依赖自身光合作用获取碳，使其能够在与丝核菌属真菌分布范围一样广泛的栖息地中生存。
