期刊
PLANT CELL AND ENVIRONMENT
卷 28, 期 10, 页码 1247-1254出版社
WILEY
DOI: 10.1111/j.1365-3040.2005.01360.x
关键词
ammonia; arbuscular mycorrhiza; external mycelium; fungal cell wall; hyphal transport; internal mycelium; nitrate; nitrification; nitrogen nutrition; symbiosis
Arbuscular mycorrhizal fungi can enhance nutrient acquisition by a plant via their extraradical hyphae. This is particularly true for phosphorus, but the case for nitrogen (N) has been less clear. In our growth systems there was a small air-gap between root and hyphal compartments, which eliminated diffusion of nutrients between compartments. Moreover, our methods allowed us to distinguish between nitrate and ammonium. We found that N transfer to Zea maize L. depends on the sources fed to the hyphae of Glomus aggregatum Schenck & Smith. In experiment 1, despite the fact that plant demand for N was already met, plants received 10 times as much N-15 from ammonium than from nitrate. In experiment 2, 74% of shoot-N was derived from the slow-release urea added to the hyphal compartment while only 2.9% was derived from the nitrate-N. Intraradical hyphae isolated from roots contained a considerable amount of N-15 in the cell wall even when N-15-nitrate was the source. We conclude that the mycorrhizal fungus can rapidly deliver ammonium-N to the plants, and that while the fungus can absorb nitrate, it apparently lacks the capacity to transfer it to the plant.
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