Evaluation of some methods for enumeration of nitrogen fixing blue green algae in soil

Othman R.; Wollum A. G. II

Studies were conducted to investigate the effect of shaking time, medium pH value, and medium composition on the total number and diversity of nitrogen-fixing blue-green algae present in soils. The algal populations were enumerated from surface soil (0-2 cm) using a most-probable-number (MPN) procedure. The different shaking times used included: 5, 15, 30, and 45 min. Five medium acidity levels were included also and were: pH 5.0, 5.5, 6.0, 6.5, and 7.0, while the four N-free media were Bold Basal, Gorham, BG-II, and Watanabe. Shaking time had no influence on the total algal population. However, significantly higher algal counts were observed at medium of pH 6.0 as compared to the other acidity levels studied. Enumeration using the Bold Basal medium resulted in the greatest numbers of algae determined. The diversity of the species composition was affected also by variations in the cultural conditions studied. Nostoc was the most common genus encountered and was apparently the most tolerant to changes in medium pH value and composition of any of the different algae observed. Standardizing the cultural conditions for determining algal populations would permit valid comparisons of population dynamics within a site.