The biotic and abiotic net change of bioavailable carbon was measured as water extractable organic carbon (EOC) near the interface of soil and lignocellulose. The influence on EOC of growth and interaction of a white rot fungus and the indigenous soil microorganisms was studied. During decomposition of straw by Pleurotus sp. or Dichomitus squalens, EOC in straw increased from 18 to 39-83 mg g(-1). Nevertheless, only low amounts of EOC were translocated into the adjacent soil. When sterile straw was brought into contact with nonsterile soil, consumption of EOC by the soil microorganisms in the straw was higher than the EOC flux from straw into soil. During simultaneous growth of white rot fungi and soil organisms, propagation of soil bacteria in straw and growth of the fungal mycelia in soil were partially inhibited. However, the accumulation of EOC in straw by the fungi continued in the presence of soil microbiota.