Mycorrhizal weathering: A true case of mineral plant nutrition?

Weatherable minerals in all podzol surface soils andshallow granitic rock under European coniferousforests studied hitherto are criss-crossed bynumerous open, tubular pores, 3–10 µm in width. Wehypothesize that these pores were formed bycomplex-forming, low-molecular weight organic acidsexuded by or formed in association with mycorrhizalfungi. It is well known that ectomycorrhizal myceliumrepresents a greatly extended, and better distributed,surface area for the absorption of nutrients. However, there have been few investigations of how thewhereabouts of individual hypha affect nutrientuptake. The results presented here provide directevidence that the mycelium is able to penetrate, andmost probably create, microsites which areinaccessible to plant roots and isolated from bulksoil solution phenomena. Dissolved products could betranslocated to the host plant roots, bypassing thesoil solution with often toxic concentration ofAl3+ from acid rain, and bypassing competitionfor nutrient uptake by other organisms. Furthermore,there is strong evidence that ``rock-eating''mycorrhizal fungi play a role in the formation ofpodzol E horizons. The partly speculativeinterpretations presented here challenge conventionalideas about (1) the importance of nutrient uptakefrom the bulk soil solution (2) criteria for criticalloads of acid atmospheric deposition for forests, and(3) the process of podzolization.