| 1. |
- van Breemen, Nico, et al.
(författare)
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Do plants drive podzolization via rock-eating mycorrizhal fungi?
- 2000
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 94:2-4, s. 163-171
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Tidskriftsartikel (refereegranskat)abstract
- Weathering and supply of nutrients derived from minerals to plants is known to be stimulated by plant symbiotic mycorrhizal fungi. Nutrients are generally thought to pass the bulk soil solution before plant uptake. Jongmans et al. [Jongmans, A.G., van Breemen, N., Lundstrom, U.S., van Hees, P.A.W., Finlay, R.D., Srinivasan M., Unestam, T., Giesler, R., Melkerud, P.-A., Olsson, M., 1997. Rock-eating fungi. Nature, 389, 682-683] showed that (ectomycorrhizal) fungi drill innumerable narrow cylindrical pores (diameter 3-10 μm) into weatherable minerals in podzol E horizons. The fungi probably form micropores by exuding strongly complexing low-molecular weight organic acids at their hyphal tips, causing highly local dissolution of Al silicates. Micropores occurred in all thin sections of podzols under Pinus sylvestris and Picea abies available from Sweden (3), Finland (2), Switzerland (2), Denmark (2) and the Netherlands (3), but not in the few available thin sections of non-podzolic soils under broadleaves. Many weatherable minerals in the podzol E horizon appeared to be perforated, as opposed to few if any in the abruptly underlying B horizon, suggesting a link to podzolization. High concentrations of Al and Si in organic surface horizons under boreal and temperate conifers can be explained by transfer by hypha of weathering products from the minerals to mycorrhizal roots in the O horizon, followed by release of weathering products that are not taken up by the plants. Rock-eating ectomycorrhizal fungi suggest a more direct role for plants in podzolization than hitherto realized, providing tight coupling between podzolization and mineral weathering. Preliminary observations, however, indicate that mycorrhizal fungi do not play a role in podzolization under Kauri (Agathis australis) in New Zealand. (C) 2000 Elsevier Science B.V.
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| 2. |
- van Breemen, Nico, et al.
(författare)
-
Mycorrhizal weathering : A true case of mineral nutrition?
- 2000
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Ingår i: Biogeochemistry. - 0168-2563 .- 1573-515X. ; 49:1, s. 53-67
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Tidskriftsartikel (refereegranskat)abstract
- Weatherable minerals in all podzol surface soils and shallow granitic rock under European coniferous forests studied hitherto are criss-crossed by numerous open, tubular pores, 3-10 μm in width. We hypothesize that these pores were formed by complex-forming, low-molecular weight organic acids exuded by or formed in association with mycorrhizal fungi. It is well known that ectomycorrhizal mycelium represents a greatly extended, and better distributed, surface area for the absorption of nutrients. However, there have been few investigations of how the whereabouts of individual hypha affect nutrient uptake. The results presented here provide direct evidence that the mycelium is able to penetrate, and most probably create, microsites which are inaccessible to plant roots and isolated from bulk soil solution phenomena. Dissolved products could be translocated to the host plant roots, bypassing the soil solution with often toxic concentration of Al3+ from acid rain, and bypassing competition for nutrient uptake by other organisms. Furthermore, there is strong evidence that 'rock-eating' mycorrhizal fungi play a role in the formation of podzol E horizons. The partly speculative interpretations presented here challenge conventional ideas about (1) the importance of nutrient uptake from the bulk soil solution (2) criteria for critical loads of acid atmospheric deposition for forests, and (3) the process of podzolization.
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