Suetsugu Kenji, Matsubayashi Jun, Tayasu Ichiro
Department of Biology, Graduate School of Science, Kobe University, Kobe, Hyogo, 657-8501, Japan.
Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, 237-0061, Japan.
New Phytol. 2020 Sep;227(5):1519-1529. doi: 10.1111/nph.16409. Epub 2020 Feb 3.
Mycoheterotrophic plants depend entirely on fungal associations for organic nutrients. While most mycoheterotrophic plants are associated with the mycorrhizal partners of surrounding green plants, some mycoheterotrophs are believed to obtain carbon from decaying litter or dead wood by parasitising saprotrophic fungi, based on culture experiments and C and N isotopic signatures. The carbon age (the time since carbon was fixed from atmospheric CO by photosynthesis) can be estimated by measuring the concentration of C arising from the bomb tests of the 1950s and 1960s. Given that mycorrhizal fungi obtain photosynthate from their plant partners, and saprotrophic wood-decaying fungi obtain carbon from older sources, radiocarbon could represent a new and powerful tool to investigate carbon sources of mycoheterotrophic plants. We showed that the Δ C values of mycoheterotrophs exploiting ectomycorrhizal fungi were close to 0‰, similar to those of autotrophic plants. By contrast, the Δ C values of mycoheterotrophs exploiting saprotrophic fungi ranged from 110.7‰ to 324.8‰, due to the C-enriched bomb carbon from dead wood via saprotrophic fungi. Our study provides evidence supporting that some mycoheterotrophic orchids depend on forest woody debris. Our study also indicates that radiocarbon could be used to predict the trophic strategies of mycoheterotroph-associated fungal symbionts.
菌根异养植物完全依赖真菌共生关系获取有机养分。虽然大多数菌根异养植物与周围绿色植物的菌根伙伴相关联，但基于培养实验以及碳和氮同位素特征，一些菌根异养植物被认为是通过寄生腐生真菌从腐烂的凋落物或枯木中获取碳。碳年龄（自碳通过光合作用从大气二氧化碳中固定以来的时间）可以通过测量20世纪50年代和60年代核弹试验产生的碳的浓度来估算。鉴于菌根真菌从其植物伙伴那里获取光合产物，而腐生木材腐朽真菌从较老的来源获取碳，放射性碳可能是研究菌根异养植物碳源的一种新的有力工具。我们发现，利用外生菌根真菌的菌根异养植物的δ¹³C值接近0‰，与自养植物的δ¹³C值相似。相比之下，利用腐生真菌的菌根异养植物的δ¹³C值在110.7‰至324.8‰之间，这是由于来自枯木的富含¹³C的核弹碳通过腐生真菌所致。我们的研究提供了证据支持一些菌根异养兰花依赖森林木质残体。我们的研究还表明，放射性碳可用于预测与菌根异养植物相关的真菌共生体的营养策略。
