Laboratory of Forest Pathology and Mycology, Graduate School of Bioresources, Mie University, Japan.
Am J Bot. 2012 Jul;99(7):1177-88. doi: 10.3732/ajb.1100546. Epub 2012 Jun 27.
Mixotrophy is a strategy whereby plants acquire carbon both through photosynthesis and heterotrophic exploitation of mycorrhizal fungi. In Euro-American Pyroleae species studied hitherto, heterotrophy levels vary according to species, sites of study, and possibly light conditions. We investigated mycorrhizal association and mixotrophy in the Asiatic forest species Pyrola japonica, and their plasticity under different light conditions.
Pyrola japonica was sampled bimonthly in sunny and shaded conditions from a deciduous broadleaf forest. We microscopically assessed the rate of fungal colonization and sequenced the ITS to identify the mycorrhizal fungi. We measured (13)C and (15)N isotopic abundances in P. japonica as compared with neighboring autotrophic and mycoheterotrophic plants, to evaluate P. japonica's heterotrophy level.
Pyrola japonica formed arbutoid mycorrhizas devoid of fungal mantles, with intracellular hyphal coils and a Hartig net. It tended to be more colonized by mycorrhizal fungi in spring and summer. Most associated fungi belonged to ectomycorrhizal taxa, and 84% of identified fungi were Russula spp. Rate of mycorrhizal colonization and Russula frequency tended to be higher in shaded conditions. Both δ(13)C and δ(15)N values of P. japonica were significantly higher in autotrophic plants, showing that about half of the carbon on average was received from mycorrhizal fungi. Both isotopic values negatively correlated with light availability, suggesting higher heterotrophy levels in shaded conditions.
The mixotrophic P. japonica undergoes changes in mycorrhizal symbionts and carbon nutrition according to light availability. Our results suggest that during Pyroleae evolution, a tendency to increased heterotrophy emerged in the Pyrola/Orthilia clade.
混养是一种策略，通过这种策略，植物既可以通过光合作用，也可以通过利用菌根真菌的异养方式获取碳。在迄今为止研究过的欧美 Pyroleae 物种中，异养水平因物种、研究地点和可能的光照条件而异。我们调查了亚洲森林物种 Pyrola japonica 的菌根共生和混养，并研究了它们在不同光照条件下的可塑性。
在落叶阔叶林的阳光和阴影条件下，每两个月对 Pyrola japonica 进行一次采样。我们通过显微镜评估真菌定殖率，并对 ITS 进行测序以鉴定菌根真菌。我们测量了 P. japonica 与相邻自养和菌异养植物的 (13)C 和 (15)N 同位素丰度，以评估 P. japonica 的异养水平。
Pyrola japonica 形成缺少真菌套的石楠型菌根，具有细胞内菌丝线圈和 Hartig 网。它在春季和夏季往往更容易被菌根真菌定殖。大多数相关真菌属于外生菌根类群，84%鉴定出的真菌属于 Russula 属。在阴影条件下，菌根定殖率和 Russula 频率往往更高。P. japonica 的 δ(13)C 和 δ(15)N 值在自养植物中显著较高，表明平均约有一半的碳来自菌根真菌。这两个同位素值与光照可用性呈负相关，表明在阴影条件下具有更高的异养水平。
混养的 P. japonica 根据光照可用性改变菌根共生体和碳营养。我们的结果表明，在 Pyroleae 进化过程中，Pyrola/Orthilia 分支出现了异养倾向增加的趋势。
