Data from: Stable isotope signatures of underground seedlings reveal the organic matter gained by adult orchids from mycorrhizal fungi

1.Orchids produce dust seeds dependent on the provision of organic carbon by mycorrhizal fungi for their early development stages. Hence, all chlorophyllous orchids experience a dramatic switch in trophic strategies from initial mycoheterotrophy to either autotrophy or partial mycoheterotrophy during ontogeny. Yet, the degree to which partially mycoheterotrophic orchids gain carbon from their mycorrhizal fungi is unclear based on existing approaches.

2.Here, we propose a novel approach to quantify the fungal-derived organic matter gain of chlorophyllous mature orchids mycorrhizal with rhizoctonia fungi using the stable isotope signatures of their fully mycoheterotrophic (FMH) seedlings in a linear two-source mixing model.

3.We conducted a field germination experiment with seven orchid species and measured carbon, nitrogen and hydrogen stable isotope natural abundances and nitrogen concentrations of mature orchids, underground seedlings and autotrophic references.

4.After in situ burial for 19 – 30 months, germination rates varied considerably among five orchid species and failed for two. On average, underground seedlings were enriched in 13C and 15N relative to mature orchids and had higher nitrogen concentrations. Using the mean enrichment factors ε13C and ε2H of seedlings as FMH endpoint, the organic matter gain derived by mature orchids from mycorrhizas was ca. 20%.

5.Chlorophyllous orchids mycorrhizal with rhizoctonias are predisposed to partially mycoheterotrophic nutrition due to their initially mycoheterotrophic seedling stage. We show that the carbon and hydrogen isotope abundances of underground seedlings can be used in an improved mixing-model to identify a significant proportion of fungal-derived organic matter in mature orchids.

1.兰科植物产生粉尘状种子，其早期发育阶段依赖菌根真菌提供有机碳。因此，所有具叶绿素的兰科植物在个体发育过程中，营养策略会发生剧烈转变：从初始的菌异养阶段切换为自养或部分菌异养营养模式。然而，基于现有研究方法，部分菌异养兰科植物从菌根真菌中获取碳的具体比例仍不明确。
2.在此，我们提出一种全新方法，通过线性双源混合模型，利用完全菌异养（FMH）幼苗的稳定同位素特征，量化与丝核菌属真菌形成菌根的具叶绿素成熟兰科植物所获得的真菌源有机质占比。
3.我们针对7种兰科植物开展了野外萌发实验，测定了成熟兰科植物、地下幼苗以及自养参照样本的碳、氮、氢稳定同位素自然丰度与氮元素浓度。
4.经原位埋藏19至30个月后，5种兰科植物的萌发率存在显著差异，剩余2种未成功萌发。平均而言，地下幼苗的13C与15N丰度高于成熟兰科植物，且氮元素浓度也更高。以幼苗的ε13C和ε2H平均富集因子作为完全菌异养终点，成熟兰科植物从菌根中获取的有机质占比约为20%。
5.与丝核菌属真菌形成菌根的具叶绿素兰科植物，由于其幼苗阶段初始为菌异养，因此天然倾向于采用部分菌异养的营养方式。本研究表明，可借助改进的混合模型，利用地下幼苗的碳、氢同位素丰度，鉴定出成熟兰科植物体内占比可观的真菌源有机质。