Review and synthesis of experimental data on organic matter decomposition with respect to the effect of temperature, moisture, and acidity

Abstract

A review and synthesis of experimental decomposition data was performed with the objective of finding parameter values for a decomposition model. Experimental data were retrieved from the literature and included data on mass loss rates, nitrogen mineralization rates, carbon dioxide evolution rates, and growth rates of bacteria and fungi. Environmental variables included in the synthesis were air temperature, soil moisture, and soil acidity (concentration of H+ and Al3+ in soil solution). The variables were assumed to act as separate, multiplicative rate regulating factors on soil microbial processes. The model outline includes four organic matter pools: (i) easily decomposable compounds, (ii) holocellulose, (iii) lignin, and (iv) resistant compounds. It was assumed that the decomposition of the easily decomposable substances can be modeled as the growth rate of bacteria, while the decomposition of lignin and resistant compounds can be modeled as the growth rate of fungi. The decomposition of the substances included in the holocellulose pool was assumed to follow an intermediate function. Results show that enough data are available for the parameterization of a model of the suggested type. The effect of temperature on decomposition rate seems to increase with decreasing nutrient concentration of the substrate. Decomposition rates increase with relative soil moisture saturation. Bacterial growth rates are generally more sensitive to low pH than fungal growth rates. Decomposition of mixed organic material is inhibited in an intermediate fashion. The combined impact of H+ and Al3+ on the growth rates of bacteria and fungi can be modeled with an ion-exchange expression, preferably the Vanselow expression. It was concluded that some additional experiments would be needed for further model development purposes. Such experiments should be set up as mass loss experiments and last for a minimum of 2 weeks.Key words: decomposition, model, acidification, aluminum, pH.