Oxalic acid and Agaricus

[Jessie Micales]

I recently had a mushroom producer contact me about oxalic acid formation 
by Agaricus.  He says that about 20% of the carbon content of the compost 
is lost to oxalic acid formation rather than the production of mycelium.  
Has anyone here done any work with oxalic acid production by Agaricus or 
other commercial fungi or has made similar observations?  Brown-rot wood 
decay fungi also make a lot of oxalic acid.  I wonder whether these are 
related phenomena or totally different aspects of similar 
physiology. 

Any ideas, references, or passing thoughts appreciated!

Jessie A. Micales (jmicales at facstaff.wisc.edu)