Ap. Oliveira et Me. Pampulha, Occurrence of nitrogen-fixing activity and aerobic heterotrophic N-2-fixing populations in Portuguese soils, J BASIC MIC, 38(5-6), 1998, pp. 389-393
Nitrogen-fixing activity in three different soil types was measured by the
acetylene reduction method. N-2-fixation ranged from 0.38 to 6.89 nmoles C2
H4 . h(-1) . g(-1) soil dry weight. Activity of nitrogen-fixing microorgani
sms was positively correlated with the moisture content of the soil samples
. Populations of aerobic, heterotrophic, N-2-fixing microorganisms were est
imated by dilution plate counts on three commonly used semisolid media. The
different carbon sources in the media markedly influenced the counts. In g
eneral a multiple carbon source medium gave the highest counts and was chos
en for future work.