Abstract
The occurrence and the dynamics of phototrophic purple nonsulphur bacteria (PPNSB) as well as Azospirillum, Azotobacter, Clostridium, and cyanobacteria at different rice growth stages were studied in two ricefields, at Kafr-El-Shiekh and Al-Fayoum in Egypt. The PPNSB existed in the both rice fields examined, but their numbers varied according to field conditions, habitat and rice growth stage. After transplanting, the number of PPNSB increased gradually, reached its maximum at maximum tillering stage, and thereafter declined toward harvest time. Numbers of PPNSB were generally comparable with that of the heterotrophic N2-fixers namely Azospirillum, Azotobacter, Clostridium and cyanobacteria, while that of phototrophic purple and green sulphur bacteria were relatively lower. The highest PPNSB numbers were generally found in rhizosphere (103–106 per g−1 dw soil) followed by soil (103–105 per g−1 dw soil) and floodwater (10–102 per ml). Rice plants showed a positive rhizosphere effect on PPNSB, clostridia, Azotobacter and Azospirillum, negative rhizosphere effect on cyanobacteria and green sulphur bacteria, and no effect on purple sulphur bacteria.
Published Version
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