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In addition, wood decomposing fungi produce large amounts of oxalic acids when degrading wood \citep{Dutton_1996}, which may have secondary effects on phosphorous release from the soil \citep{Fransson_2004}.    It is not clear if organic acid release and acidification is a primary mechanism to release nutrients from soil minerals, or a secondary effect related to the way microorganisms are growing in the soil.  \citet{van_Scholl_2006a} studied organic acid production in relation to nutrient availabily for several mycorrhizal fungi growing in vitro or in symbiosis with a host tree.  Protons are exuded in response to uptake of positively charged ions regardless of if minerals are present or not, and exudation of organic acids can occur in response to many different factors such as pathogenesis and detoxification of heavy metals \cite{Dutton_1996}.  Furthermore, concentrations of \citep{chadwick_changing_1999}.\citet{van_Scholl_2006a} studied  organic acids acid production  in soil solution \citep{van_Hees_2000} seldom reach levels that have significant effects relation to nutrient availabily for several mycorrhizal fungi growing *in vitro* or in symbiosis with a host tree. There was no clear trend in responses among the different species  on mineral dissolution \citep{chadwick_changing_1999}. different nutrient levels.  Furthermore, concentrations of organic acids in soil solution \citep{van_Hees_2000} seldom reach levels that have significant effects on mineral dissolution.  On the other hand, fungal hyphae attach to surfaces to be able to grow and proliferate through the soil, which may affect the surface of the minerals both physically and chemically \citep{McMaster_2008}.   When attached to the surfaces, fungi form a layer of extracellular polyermic substances (EPS) around the hyphae. \citet{Balogh_Brunstad_2008} suggested that organic acids may accumulate under such biolayers to sufficient concentrations to affect mineral dissolution. Although these authors call for more experiments to confirm this possible effect.