ABSTRACT
The products of photosynthesis in plants, algae, and some eubacteria are the basic food sources for terrestrial animals, fungi, bacteria, and eukaryotic microorganisms-both aboveground organisms and those in soils (Figure 9.1). Animals are the major feeders on plant materials aboveground, but smaller organisms, including many invertebrate animals, dominate the belowground activity (Mitchell 1988; Killham 1994; Coleman et al. 2004; Bardgett 2005; and a well-illustrated book by Nardi 2007). Living organisms are involved in practically all soil organic matter transformations. Earthworms, ants, termites, and larger animals mix organic detritus into soils, and redistribute organic matter within soils. Then soil microorganisms decompose the organic matter that has not been digested by the animals, or by microorganisms in the digestive tracts of the animals. Microorganisms are essential in breaking the organic matter down to components that can be reused by plants or other soil organisms, rather than allowing all of the organic matter to accumulate in soils. Enzymes of microorganisms are biological catalysts mediating soil organic matter reactions that would be very slow, or not even occur, in an abiotic environment.
