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considerably for different soils (Korom, 2008), suggesting that additional factors may
also be involved and may be more controlling than temperature alone.
While a wide variety of studies show denitrification is effective across a range of
temperatures, it is clear that the lower the temperature the lower is the feasibility of the
occurrence of denitrification; this is one of the reasons why many research studies place
samples in a reduced temperature environment for storage and transport from field to the
lab for analysis.
1.2.5. pH
The pH range preferred by heterotrophic denitrifiers is generally between 5.5 and 8.0
(Rust et al., 2000). The pH range reported in soils showing denitrification by Fukada et
al., (2003) have a much narrower range of 7.1 – 7.9. Brettar and Hofle (2002) reported
the occurrence of denitrification in soils ranging from 7.5 – 8.5. Barkle et al. (2007)
demonstrated the capacity for denitrification in soils with pH ranging from 5.1 – 6.8.
Tiedje et al. (1982) however observe the occurrence of denitrification in soils with a wide
range of pH. Their data demonstrate the occurrence of denitrification in soils with pH
ranging from 4.0 to 7.1, thus showing that denitrification is possible in acidic
environments. In addition once denitrification begins it can increase pH by releasing CO2
and hydroxide (OH - ). Normally these combine to yield HCO3 - , but if the production of
OH - exceeds that of CO2, the pH can rise (Simek and Cooper, 2002).
At low concentrations of
However at
−
NO 3 soil acidity has little influence on the N2O/N2 ratio.
−
NO 3 concentrations above 10 ppm, the more acidic the soil the greater the
amount of N2O produced (Firestone et al., 1980, Glass and Silverstein, 1998). pH values
outside the range of 4.0 - 7.1 may hinder the denitrification process, but the optimal pH is
site-specific because of the effects of acclimation and adaptation of the microbes to the
ecosystem (Simek et al., 2002).
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