ORGANIC MATTER DECOMPOSITION, GREENHOUSE GASES, MICROBIAL BIOMASS IN SOIL AND COMPOST
Decomposition of organic matter involves four component processes: photo-oxidation, leaching, comminution, and mineralization. Arthropods are key factors influencing comminution and mineralization. Decomposition most commonly is measured as respiration rate, as the ratio of litter input to litter standing crop, or as the rate of litter disappearance. Isotopic tracers also provide data on decomposition rate. Decomposition rate typically is higher in mesic than in arid ecosystems. Decomposition generally can be modeled as a multiple negative exponential decay function over time, with decay constants proportional to the quality of litter components. Detritivores affect decomposition through comminution, effects on microbial biomass, and effects on mineralization. Comminution increases detrital surface area and facilitates colonization and decay by microflora. Not all organic material is converted to CO2. The low oxygen concentrations characterizing warm, humid termite colonies favor incomplete reduction of organic molecules to methane and other trace gases. Detritivores often increase mineralization of nitrogen, but nitrogen released from detritus may be immobilized quickly by microorganisms. Burrowers affect soil development by redistributing soil and organic matter. Ants and termites, in particular, excavate large volumes of soil and accumulate organic material in their centralized nests, mixing soil with organic material and influencing the distribution of soil nutrients and organic matter. Surrounding soils may become depleted in soil carbon and nutrients. Detritivore and burrower effects on mineralization and soil composition can increase plant growth, alter vegetation structure, and increase herbivory.