Cellulase Activity in Physically Isolated Fractions of a Paddy Soil

Specific location of extracellular enzymes within the soil matrix was related to soil organic matter (SOM) quality and carbon turnover. A physical fractionation procedure was used to investigate whether soil carbon was spatially isolated from degradative enzymes in a paddy soil. In POM fractions of this study, high C concentrations are found because they are derived from inputs of recent plant materials with high C-to-N ratios and low mineral content. Total nitrogen was highest in the clay-sized fraction and lowest in the silt-sized fraction. The C-to-N ratios were decreased with decreasing particle size, lowest in the clay-sized fraction, greatest in the POM fractions, and inter-mediate in the bulk soil and silt-sized fractions. Different distribution trend in physically isolated fractions indicated that there was fundamental difference in the factors determining their location. The absolute activity of carboxymethyl cellulase activity was greatest in coarse POM fractions and generally decreased from the coarse POM fractions to the silt-size fraction, following a decrease of Corg as well as an increase in bio-stability of the organic material, as indicated by a decrease in the C-to-N ratio.