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 sit...1. 兰科植物可产生粉尘状种子，其早期发育阶段依赖菌根真菌（mycorrhizal fungi）供给有机碳。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：从初始的菌异养转向自养或部分菌异养。然而，依托现有研究方法，学界仍难以明确部分菌异养兰科植物从菌根真菌中获取碳的具体程度。 2. 本研究提出一种全新方法：借助完全菌异养（fully mycoheterotrophic，FMH）实生苗的稳定同位素特征，通过线性双源混合模型，量化与丝核菌（Rhizoctonia）菌根共生的成熟具叶绿素兰科植株的真菌源性有机碳获取量。 3. 本研究针对7种兰科植物开展野外萌发实验，测定了成熟兰科植株、地下实生苗以及自养参照组的碳、氮、氢天然稳定同位素丰度与氮元素浓度。 4. 经原位……