Direct nocturnal water transfer from oaks to their mycorrhizal symbionts during severe soil drying
Direct nocturnal water transfer from oaks to their mycorrhizal symbionts during severe soil drying
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DOI：
10.1007/s00442-002-1078-2
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发表时间：
2003-01-01
期刊：
影响因子：
2.7
通讯作者：
Allen, MF
中科院分区：
文献类型：
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作者：
Querejeta, JI;Egerton-Warburton, LM;Allen, MF
共生菌根真菌在大多数植物对土壤养分和水分的吸收中起着重要作用。有人认为，在干旱条件下，水力举升的水可以保持外部菌根菌丝体的完整性。我们在专门的菌根物种，海岸活橡树（Quercus agrifolia）中测试了这一假设，使用一个微观系统，将根部的液压提升效应与外部菌丝体的液压提升效应分开。菌根栎树幼苗建立在由三个独立隔间组成的微环境中：(1)上部根，(2)主根，(3)外部真菌菌丝体。种植8个月后，开始干旱处理：停止对上根和真菌室的灌溉，只维持对主根室的灌溉。干旱3、12、30、50、70和80天后，黄昏时将示踪剂注入主根室。次日黎明，用示踪剂广泛标记上根室和真菌室的菌根菌丝（EM和AM）和孢子（AM）。相比之下，当白天将示踪剂注射到主根室时，没有观察到标记。夜间从植物到菌根真菌的水分转运与液压升降机有关。微生物中的腐养/寄生真菌没有被标记，这表明水分直接从植物转移到它们的菌根共生菌，而不是土壤中的其他真菌。即使在长期干旱（70-80天）后，菌根菌丝在水势值低至-20 MPa的土壤中仍然存在。在肥沃的上层土壤干燥时，通过直接水分转运维持菌根活性可能会改善深根植物的营养状况。
Symbiotic mycorrhizal fungi play an important role in the absorption of soil nutrients and water by most plants. It has been suggested that hydraulically lifted water might maintain the integrity of the external mycorrhizal mycelium during drought. We tested this hypothesis in the obligately mycorrhizal species, coast live oak (Quercus agrifolia), using a microcosm system that separated the effects of hydraulic lift in roots from those in the external mycelium. Mycorrhizal oak seedlings were established in microcosms comprising three discrete compartments for (1) upper roots, (2) tap roots, and (3) external fungal mycelium. Eight months after planting, a drought treatment was initiated: irrigation to the upper root and fungal chambers was terminated and only irrigation to the taproot compartment was maintained. After 3, 12, 30, 50, 70 and 80 days of drought, tracers were injected into the taproot compartment at dusk. At dawn the following morning, mycorrhizal hyphae (EM and AM) and spores (AM) in upper root and fungal compartments were extensively labeled with the tracers. In contrast, no labeling was observed when tracers were injected into the taproot compartment during daytime. Nocturnal water translocation from plant to mycorrhizal fungi occurred in association with hydraulic lift. Saprotrophic/parasitic fungi in the microcosms were not labeled, suggesting a direct water transfer from plants to their mycorrhizal mutualists and not to other fungi in the soil. Even after prolonged drought (70-80 days), mycorrhizal hyphae persisted in soils with water potential values as low as -20 MPa. Maintaining mycorrhizal activity through direct water translocation could potentially improve the nutrient status of deep-rooted plants during periods when the fertile upper soil is dry.