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author = {R. J. Howard and M. A. Ferrari and D. H. Roach and N. P. Money},
title = {Penetration of hard substrates by a fungus employing enormous turgor pressures.},
journal = {Proceedings of the National Academy of Sciences}
}" data-bib-key="Howard_1991" contenteditable="false">
Howard 1991, and also to widen existing cracks in mineral grains and rock fragments. The results of physical weathering is an increase in mineral surface area exposed to the soil solution.
Less visible is the chemical alteration or dissolution of minerals. Although in principle most primary minerals dissolve in soil solution, certain compounds accelerate the process. The most common, and by far quantitatively most important weathering agents are protons. Protons, and also hydroxide under alkaline conditions, attack the ion bindings in the mineral crystal lattice. This process is called hydrolysis (or carbonation when carbonic acid is the main proton donor). Biotic processes have a strong influence on the soil solution pH via the exudation of protons in exchange of positively charges nutrients as NH4+ and K+, the exudation of organic acids and the release of CO2 into the soil solution.
Organic acids like oxalic acid and citric acid, not only contribute to proton-driven weathering. Their deprotonated anions (in this case oxalate and citrate) interact in a similar way as protons and hydroxide with the mineral crystal lattice. In fact, many of the deprotonated anions of organic acids are stronger weathering agents than protons and hydroxide. They behave as strong complexants with metals including Al3+, a central element in most mineral crystal lattices.
Another set of organic compounds with metal-complexing properties are siderophores. This type of molecules form strong bindings with especially Fe3+.
To
To understand the effect impact of mycorrhizal fungi, we first need to determine what is the limiting step in the dissolution process.
process. Generally, the soil solution is far from equilibrium in respect to the primary minerals.
Close to equilibrium: saprolith, big rock fragments.
class="ltx_title_section">Fungal weathering in the lab
From lab to field
Conclusions