Nitrogen limitation in mycorrhizal Norway spruce (Picea abies) seedlings induced mycelial foraging for ammonium: implications for Ca and Mg uptake |
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Authors: | Jentschke Georg Godbold Douglas L. Brandes Bettina |
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Affiliation: | (1) School of Agricultural and Forest Sciences, University of Wales Bangor, Bangor, Gwynedd, LL57 2UW, UK;(2) Forest Ecosystem Research Center, Institute of Forest Botany, University of Göttingen, Büsgenweg 2, D-37077 Göttingen, Germany |
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Abstract: | Although many studies support the importance of the external mycelium for nutrient acquisition of ectomycorrhizal plants, direct evidence for a significant contribution to host nitrogen nutrition is still scarce. We grew nonmycorrhizal seedlings and seedlings mycorrhizal with Paxillus involutus (Batsch) Fr. in a sand culture system with two compartments separated by a 45-m Nylon mesh. Hyphae, but not roots, can penetrate this net. Nutrient solutions were designed to limit seedling growth by nitrogen. Hyphal density in the hyphal compartment, host N status and shoot growth of mycorrhizal seedlings significantly increased in response to NH4+ addition to the hyphal compartment. Labeling the compartment only accessible to hyphae with 15NH4+ showed that the increase in N uptake in the mycorrhizal seedlings was a result of hyphal N acquisition from the hyphal compartment. These results indicate that hyphae of P. involutus may actively forage into N-rich patches and improve host N status and growth. In the mycorrhizal seedlings, which received additional NH4+ via their external mycelium, the increase in NH4+ supply less negatively affected Ca and Mg uptake than in nonmycorrhizal seedlings, where the additional NH4+ was directly supplied to the roots. This was most likely due to the close link of NH4+ uptake and H+ extrusion, which, in the nonmycorrhizal seedlings, lead to a strong acidification in the root compartment, and subsequently reduced Ca and Mg uptake, whereas in the mycorrhizal seedlings the site of intensive NH4+ uptake and acidification was in the hyphal and not in the root compartment. Our data support the idea that the ectomycorrhizal mycelium connected to an N-deficient host may actively forage for N. The mycelium may also be important as a biological buffer system ameliorating negative influence of high NH4+ supply on cation uptake. |
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Keywords: | calcium ectomycorrhiza hyphal transport magnesium nitrogen nutrition Paxillus involutus Picea abies |
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