Regulators of Nitrate Reduction

Oxygen content of the soil has no effect on anabolic nitrate reduction, as aerobes use nitrate as nutrient source and reduce it to ammonia during cell synthesis. The assimilative nitrate reductases are soluble proteins and are repressed by high ammonia levels. 

Presence of nitrogen oxides Nitrate reduction in wetlands is often limited by the availability of nitrogen oxides including nitrate. Sources of nitrate in wetlands are point and nonpoint sources from adjacent watersheds, groundwater inputs, atmospheric deposition, nitrification of ammonium in aerobic zones, and nitrification of ammonium released from anaerobic soil layers either by diffusion, advection, or bioturbation. Nitrate loading to most wetlands 

FIGURE 8.43 Effect of oxygen concentration on denitrification rates. (Modified from Tiedje, 1988.) 

In interior wetland areas, the source of nitrate is primarily nitrification, and denitrification rates in these areas are limited by nitrate availability. Several studies have shown that denitrification rates increase with an increase in nitrate concentration. Half-saturation constants (one of the Michaelis-Menton kinetics parameter) reported for denitrification range from 27 to 344 pM for lake and marine sediments (Seitzinger, 1988) and 130 to 1,200 pM for soils (Firestone, 1982). Low half-saturation constants probably reflect carbon limitation in soil or diffusion of nitrate from aerobic sites to anaerobic sites. 

Nitrate reduction rates have been shown to be highly correlated to soil organic matter and soluble or available organic carbon (determined as extractable organic carbon) in soils. Several studies have shown a strong relationship between nitrate reduction and available carbon in soils (Buford and Bremner, 1975 Reddy et al., 1982). Nitrate reduction in wetland soils can be coupled to organic matter mineralization (see Chapter 5), as facultative bacteria use 

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