Arbuscular mycorrhizal (AM) fungi play a positive role in plant water relations, and the AM symbiosis is often cited as beneficial for overcoming drought stress of host plants. Nevertheless, water uptake via mycorrhizal hyphal networks has been little addressed experimentally, especially so through isotope tracing. In a greenhouse study conducted in two-compartment rhizoboxes, Medicago truncatula was planted in the primary compartment (PC), either inoculated with Rhizophagus irregularis or left uninoculated. Plant roots were either allowed to enter the secondary compartment (SC) or were restricted to the PC by root-excluding mesh. Substrate moisture was manipulated in the PC such that the plants were grown either in high moisture (15% of gravimetric water content, GWC) or low moisture (8% GWC). Meanwhile, the SC was maintained at 15% GWC throughout and served as a water source accessible (or not) by roots and/or hyphae. Water in the SC was labeled with deuterium (D) to quantify water uptake by the plants from the SC. Significantly, increased D incorporation into plants indicated higher water uptake by mycorrhizal plants when roots had access to the D source, but this was mainly explained by generally larger mycorrhizal root systems in proximity to the D source. On the other hand, AM fungal hyphae with access to the D source increased D incorporation into plants more than twofold compared to non-mycorrhizal plants. Despite this strong effect, water transport via AM fungal hyphae was low compared to the transpiration demand of the plants.

中文翻译：

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丛枝菌根真菌促进植物水分的吸收：根和菌丝的高第氏结。

丛枝菌根（AM）真菌在植物水分关系中起着积极作用，而且AM共生常被认为对克服寄主植物的干旱胁迫有益。然而，通过菌根菌丝网络吸收水的实验很少，尤其是通过同位素示踪法。在一个两室的根瘤菌箱进行的温室研究中，将截叶苜蓿种植在主要室（PC）中，接种了不规则的根瘤菌或不接种。允许植物根部进入次生区室（SC）或通过根系不包含网眼限制在PC上。在PC中处理基质水分，使植物在高水分（按重量计水分含量为15％，GWC）或低水分（为GWC 8％）下生长。同时，SC始终保持在15％GWC的水平，并且可以作为根部和/或菌丝可访问（或不可访问）的水源。SC中的水用氘（D）标记，以量化植物从SC中吸收的水分。值得注意的是，当根部进入D源时，增加的D掺入植物表明菌根植物对水分的吸收更高，但这主要是由于D根附近的菌根根系通常较大。另一方面，与非菌根植物相比，可利用D来源的AM真菌菌丝将D掺入植物的比例增加了两倍以上。尽管有这种强大的作用，但与植物的蒸腾需求相比，通过AM真菌菌丝的水运输仍然很低。