It is believed that resource exchange, which is responsible for intensified growth of ectomycorrhizal plants, occurs in the fungus-plant interface. However, increasing evidence indicates that such intensified plant growth, especially root growth promotion, may be independent of root colonization. Nevertheless, the molecular adjustments in low-colonized plants remain poorly understood. Here, we analyzed the metabolome of Populus × canescens microcuttings characterized by significantly increased growth triggered by inoculation with Paxillus involutus, which successfully colonized only 2.1 ± 0.3% of root tips. High-throughput metabolomic analyses of leaves, stems and roots of Populus × canescens microcuttings supplemented with leaf proteome data were performed to determine ECM-triggered changes in N-, P- and C-compounds. The molecular adjustments were relatively low in low-colonized (M) plants. Nevertheless, the levels of foliar phenolic compounds were significantly increased in M plants. Increases of total soluble carbohydrates, starch as well as P concentrations were also observed in M leaves along with the increased abundance of the majority of glycerophosphocholines detected in M roots. However, compared with the leaves of the non-inoculated controls, M leaves presented lower concentrations of both N and most photosynthesis-related proteins and all individual mono- and disaccharides. In M stems, only a few compounds with different abundances were detected, including a decrease in carbohydrates, which was also detected in M roots. Thus, these results suggest that the growth improvement of low-colonized poplar trees is independent of an increased photosynthesis rate, massively increased resource (C:N) exchange and delivery of most nutrients to leaves. The mechanism responsible for poplar growth promotion remains unknown but may be related to increased P uptake, subtle leaf pigment changes, the abundance of certain photosynthetic proteins, slight increases in stem and root amino acid levels and the increase in flavonoids (increasing the antioxidant capacity in poplar), all of which improve the fitness of low-colonized poplars.

中文翻译：

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尽管根部定植率很低，但外生根瘤菌强烈促进了外生菌根杨的代谢组调节。

据认为，引起真菌菌根植物界面生长的资源交换是导致外生菌根植物生长加快的原因。但是，越来越多的证据表明，这种强化的植物生长，尤其是促进根系生长，可能与根系定植无关。然而，对低定殖植物的分子调节仍然知之甚少。在这里，我们分析了胡杨×canescens微切屑的代谢组，其特征在于接种渐开性Paxillus involutus可以显着增加生长，该菌仅成功定植了根的2.1±0.3％。杨树，茎叶和根的高通量代谢组学分析进行了带有叶蛋白质组数据补充的微切割，以确定ECM触发的N，P和C化合物的变化。在低定植的（M）植物中，分子调节相对较低。然而，M植物中叶酚类化合物的含量显着增加。在M叶片中还观察到总可溶性碳水化合物，淀粉以及P浓度的增加，以及在M根中检测到的大多数甘油磷酸胆碱含量的增加。但是，与未接种对照的叶片相比，M叶片的N和大多数与光合作用相关的蛋白质以及所有单个单糖和双糖的浓度均较低。在M茎中，仅检测到几种具有不同丰度的化合物，包括碳水化合物的减少，这在M根中也检测到。因此，这些结果表明，低殖民化杨树的生长改善与光合作用速率的提高，资源（C：N）的大量交换以及大多数养分向叶片的输送无关。促进杨树生长的机制尚不清楚，但可能与增加的P吸收，细微的叶子色素变化，某些光合蛋白的丰度，茎和根氨基酸含量的轻微升高和黄酮的增加有关（增加了抗氧化能力。杨树），所有这些都提高了低殖民地杨树的健康度。