Decomposition: Particulate Organic Matter

Abstract

Decomposition completes the biogeochemical cycles that photosynthesis initiates. Thus, complete decomposition results in the conversion of the organic (reduced) products of photosynthesis back into the inorganic (generally oxidized) constituents used as the reactants for photosynthesis (see Exercise 14). The major biogeochemical cycles affected by decomposition are those of C, N, P, S, and O, although it is important to realize that all of the minor constituents of biomass (cations, trace metals, etc.) also are released (mineralized) by decomposition. When plants or animals senesce and die, both dissolved (DOM) and particulate (POM) organic matter are available for degradation. Leakage of DOM from dying cells and autolysis of the tissue increase during senescence and reach maximum levels soon after death. The DOM thus produced is leached readily from the tissue into the aquatic environment and can constitute as much as 30% of the total amount of combined particulate and dissolved organic matter in lake water. This detrital DOM is available as an energy source for microflora in the sediments and waters adjacent to particulate detritus. The rate of degradation is dependent on both the enzymatic capabilities of the microflora and the environmental conditions (see Exercise 20). Some compounds of the DOM are more stable than others, but warmer temperatures and increased availability of oxygen reduce their resistence to oxidation (recalcitrance) to some extent (Godshalk and Wetzel, 1978a).