Lallemand Félix, Puttsepp Ülle, Lang Mait, Luud Aarne, Courty Pierre-Emmanuel, Palancade Cécile, Selosse Marc-André
Institut de Systématique, Évolution, Biodiversité (ISYEB), UMR 7205 CNRS MNHN UPMC EPHE, Muséum national d'Histoire naturelle, Sorbonne Universités, 57 rue Cuvier, CP39, 75005 Paris, France.
Master BioSciences, Département de Biologie, École Normale Supérieure de Lyon, Université de Lyon, UCB Lyon1, 46 Allée d'Italie, Lyon, France.
Ann Bot. 2017 Sep 1;120(3):361-371. doi: 10.1093/aob/mcx054.
In temperate forests, some green plants, namely pyroloids (Pyroleae, Ericaceae) and some orchids, independently evolved a mode of nutrition mixing photosynthates and carbon gained from their mycorrhizal fungi (mixotrophy). Fungal carbon is more enriched in 13C than photosynthates, allowing estimation of the proportion of carbon acquired heterotrophically from fungi in plant biomass. Based on 13C enrichment, mixotrophic orchids have previously been shown to increase shoot autotrophy level over the growth season and with environmental light availability. But little is known about the plasticity of use of photosynthetic versus fungal carbon in pyroloids.
Plasticity of mixotrophy with leaf age or light level (estimated from canopy openness) was investigated in pyroloids from three Estonian boreal forests. Bulk leaf 13C enrichment of five pyroloid species was compared with that of control autotrophic plants along temporal series (over one growth season) and environmental light gradients (n=405 samples).
Mixotrophic 13C enrichment was detected at studied sites for Pyrola chlorantha and Orthilia secunda (except at one site for the latter), but not for Chimaphila umbellata, Pyrola rotundifolia and Moneses uniflora. Enrichment with 13C did not vary over the growth season or between leaves from current and previous years. Finally, although one co-occurring mixotrophic orchid showed 13C depletion with increasing light availability, as expected for mixotrophs, all pyroloids responded identically to autotrophic control plants along light gradients.
A phylogenetic trend previously observed is further supported: mixotrophy is rarely supported by 13C enrichment in the Chimaphila + Moneses clade, whereas it is frequent in the Pyrola + Orthilia clade. Moreover, pyroloid mixotrophy does not respond plastically to ageing or to light level. This contrasts with the usual view of a convergent evolution with orchids, and casts doubt on the way pyroloids use the carbon gained from their mycorrhizal fungi, especially to replace photosynthetic carbon.
在温带森林中，一些绿色植物，即鹿蹄草类植物（鹿蹄草科，杜鹃花科）和一些兰花，独立进化出了一种营养模式，将光合产物与从菌根真菌获得的碳混合（混合营养）。真菌碳的13C比光合产物更富集，这使得能够估计植物生物量中从真菌异养获取的碳的比例。基于13C富集，此前已表明混合营养型兰花在生长季节和随着环境光照可利用性增加其地上部分自养水平会提高。但关于鹿蹄草类植物光合碳与真菌碳利用的可塑性知之甚少。
在爱沙尼亚三个北方森林的鹿蹄草类植物中，研究了混合营养随叶龄或光照水平（由林冠开阔度估计）的可塑性。沿着时间序列（一个生长季节）和环境光照梯度（n = 405个样本），将五种鹿蹄草类植物叶片的总13C富集与对照自养植物进行了比较。
在所研究的地点检测到了白花鹿蹄草和单侧花的混合营养13C富集（后者在一个地点除外），但对于伞形梅笠草、圆叶鹿蹄草和单花独丽花则未检测到。13C富集在生长季节或当年与上年叶片之间没有变化。最后，尽管一种共生的混合营养型兰花随着光照可利用性增加表现出13C贫化，这是混合营养型植物预期的情况，但所有鹿蹄草类植物在光照梯度下对自养对照植物的反应相同。
先前观察到的系统发育趋势得到了进一步支持：在伞形梅笠草 + 单花独丽花分支中，混合营养很少得到13C富集的支持，而在鹿蹄草 + 单侧花分支中则很常见。此外，鹿蹄草类植物的混合营养对衰老或光照水平没有可塑性反应。这与通常认为的与兰花趋同进化的观点形成对比，并对鹿蹄草类植物利用从菌根真菌获得的碳的方式，特别是替代光合碳的方式提出了质疑。
