Date of this Version
Published in Micrometeorology in Agricultural Systems (2005) Agronomy Monograph no. 47. 247-286.
Soil respiration is commonly estimated as the flux of CO2 emitted from the soil surface (Fc). It represents the sum of CO2 produced by root respiration and by heterotrophic decomposition of root exudates, soil organic matter, and plant litter. The influence of CO2 fixation by autotrophic soil microorganisms, as well as nonbiological reactions such as the chemical oxidation of organic molecules and the precipitation or dissolution of soil carbonates, is small in most situations (Suarez, 1999). Root respiration is largely regulated by the root biomass and the rate of photosynthate transfer from plant leaves and often exhibits a strong diurnal pattern. It may represent 10 to 90% of soil respiration (Hanson et al., 2000). Decomposition processes are the result of complex interactions among soil fauna, fungi, actinomycetes, and bacteria. The organisms break down complex molecules such as cellulose, hemi-cellulose, proteins and lignin into low-molecular-weight substances, which are then oxidized to CO2 to produce energy or used to provide C for cell growth. The rate of decomposition is determined by the quantity and quality of organic substrates, the efficiency and population dynamics of various decomposer groups, and the soil’s physico-chemical environment including moisture, temperature, oxygen, acidity, and redox potential (Kilham, 1994; Coleman & Crossley, 1996).