Influence of soil pH on the nitrate-reducing microbial populations and their potential to reduce nitrate to NO and N2O
1990
Nagele, W. | Conrad, R.
Slurries of an acid forest soil (pH 4.0) and two slightly alkaline agricultural soils (pH 7.6-7.8) were adjusted to pH values between 3.8 and 7.8 and tested for the nitrate-reducing potential; the percentual production of nitrite, NO, N2O and NH4(+); and the most probable number (MPN) counts of nitrate-reducing bacteria. As a general trend, pH had a 2-fold effect, i.e. nitrate-reducing potentials decreased with pH, whereas the proportions of NO, N2O and NH4(+) production increased. Experiments with chloramphenicol indicated that this behaviour was due to adaptation of the resident bacterial activity rather than to population changes. The relatively high rates of NH4(+) production indicated the presence of nitrate-ammonifying in addition to denitrifying bacteria. The population size of the nitrate-reducing bacteria was similar when MPN culture media with acid or neutral pH were used, but increased by 3 orders of magnitude when slurries of the acid soil were preincubated at neutral pH. The potential of the resident populations for nitrate reduction and growth apparently was limited but not completely precluded by low soil pH. The acid forest soil did not contain a population that was specifically adapted to the low pH in situ.
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