Microbial Biomass

In many forest ecosystems, most of the annual nutrient requirement is supplied from the decomposition of soil organic matter. Microorganisms play an essential role in completing the intrasystem nutrient cycle by releasing nutrient elements for plant uptake through the processes of decomposition and mineralization. The main biogeochemical transformations are performed by fungi and bacteria. While the number of individual soil organisms is on the order of 10⁹ per gram of soil, the amount of microbial biomass and the nutrient pools associated with this biomass is relatively small. In most forest ecosystems, soil microbe biomass comprises from 1 to 5% of the total soil organic matter pool. Because of the high concentrations of nutrients contained in microbial tissues (C/N of 10-12; C/P of 40-60), microbial biomass contains a disproportionate amount of the nutrient pool contained within organic matter, especially for nitrogen and phosphorus. As a result, the microbial biomass may contain from 3 to 15% of the nutrient pool contained within the soil organic matter.