Schiebold Julienne M-I, Bidartondo Martin I, Karasch Peter, Gravendeel Barbara, Gebauer Gerhard
Laboratory of Isotope Biogeochemistry, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, 95440 Bayreuth, Germany.
Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
Ann Bot. 2017 May 1;119(7):1085-1095. doi: 10.1093/aob/mcw265.
Partially mycoheterotrophic plants are enriched in 13 C and 15 N compared to autotrophic plants. Here, it is hypothesized that the type of mycorrhizal fungi found in orchid roots is responsible for variation in 15 N enrichment of leaf tissue in partially mycoheterotrophic orchids.
The genus Epipactis was used as a case study and carbon and nitrogen isotope abundances of eight Epipactis species, fungal sporocarps of four Tuber species and autotrophic references were measured. Mycorrhizal fungi were identified using molecular methods. Stable isotope data of six additional Epipactis taxa and ectomycorrhizal and saprotrophic basidiomycetes were compiled from the literature.
The 15 N enrichment of Epipactis species varied between 3·2 ± 0·8 ‰ ( E. gigantea ; rhizoctonia-associated) and 24·6 ± 1·6 ‰ ( E. neglecta ; associated with ectomycorrhizal ascomycetes). Sporocarps of ectomycorrhizal ascomycetes (10·7 ± 2·2 ‰) were significantly more enriched in 15 N than ectomycorrhizal (5·2 ± 4·0 ‰) and saprotrophic basidiomycetes (3·3 ± 2·1 ‰).
As hypothesized, it is suggested that the observed gradient in 15 N enrichment of Epipactis species is strongly driven by 15 N abundance of their mycorrhizal fungi; i.e. ɛ 15 N in Epipactis spp. associated with rhizoctonias < ɛ 15 N in Epipactis spp. with ectomycorrhizal basidiomycetes < ɛ 15 N in Epipactis spp. with ectomycorrhizal ascomycetes and basidiomycetes < ɛ 15 N in Epipactis spp. with ectomycorrhizal ascomycetes.
与自养植物相比，部分菌根异养植物的碳-13和氮-15含量更高。在此，我们假设在兰花根部发现的菌根真菌类型是导致部分菌根异养兰花叶片组织中氮-15含量变化的原因。
以火烧兰属为案例研究对象，测定了8种火烧兰属植物、4种块菌属真菌子实体及自养对照的碳、氮同位素丰度。利用分子方法鉴定菌根真菌。另外，从文献中收集了6种火烧兰属分类群以及外生菌根和腐生担子菌的稳定同位素数据。
火烧兰属植物的氮-15含量在3.2±0.8‰（大花火烧兰；与丝核菌相关）至24.6±1.6‰（疏花火烧兰；与外生菌根子囊菌相关）之间变化。外生菌根子囊菌的子实体（10.7±2.2‰）的氮-15含量显著高于外生菌根（5.2±4.0‰）和腐生担子菌（3.3±2.1‰）。
正如所假设的那样，火烧兰属植物氮-15含量的观测梯度强烈受其菌根真菌氮-15丰度的驱动；即，与丝核菌相关的火烧兰属植物的δ15N＜与外生菌根担子菌相关的火烧兰属植物的δ15N＜与外生菌根子囊菌和担子菌相关的火烧兰属植物的δ15N＜与外生菌根子囊菌相关的火烧兰属植物的δ15N。
