Particulate organic nitrogen decomposition

Lee, C., and C. Cronin. 1982. The vertical flux of particulate organic nitrogen in the sea decomposition of amino acids in the Peru upweUing area of the equatorial Atlantic. Journal of Marine Research 40 227-251. 

Figure 2 Stepwise decomposition of particulate organic nitrogen (PON) in arbitrary units versus time during a dark incubation. Nitrogen is transformed, first to NH4+ by bacterial ammonification and finally to NOa and NOs by the two-step process of bacterial nitrification. These same processes are responsible for the global ocean formation of NOs in the deep sea. These data are the idealized results of pioneering nitrogen cycle investigators, T. von Brand and N. Rakestraw, who unraveled these processes more than 50 years ago.

Figure 23.2 Conceptual model showing the possible fates of seagrass-hound nitrogen. Nitrogen temporarily immobilized in plant tissue can become available through exudation from live tissue, remineralization through decomposition, and grazing and subsequent excretion. Some material may be removed from the system through burial or export as dissolved or particulate organic matter.

Apparently, the particulate organic matter is oxidized, even in deep waters, but at a very slow rate. This modification of organic matter tends to the formation of very inert substances, more aliphatic molecules, refractory to further decomposition. The organic matter first loses nitrogen, phosphorus and oxygen since the activation energies for cleav e of the C—C and C—H bonds are several kcal mole" higher than those of the C—N, C—P or C—O bonds (Toth and Lerman, 1977). 

Fig. 5. A. Decomposition pattern of algal cell carbon under aerobic conditions D = dissolved organic, M = mineralised and R = residual as particulate. B. Idem for algal cell nitrogen. (After Otsuki and Hanya, 1972.)...

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