Diurnal and seasonal variations in nitrogenase activity (C 2H 2 reduction) of rice roots

Abstract

Diurnal variation of nitrogenase activity associated with rice roots was demonstrated by measuring acetylene reduction by excised roots. Diurnal N 2ase activity varied when the rice was in the early reproductive phase but not during the ripening (grain hardening) phase. These variations could not be explained by fluctuations in soil temperature alone. Seasonal variation in N 2ase activity was observed and activity was at a maximum during the plant's early reproductive phase. Nitrogen (C 2H 2) fixation was linear for a 2 h incubation during the early reproductive phase of the plants, but not during the ripening phase. This study confirms the hypothesis that associative N 2ase activity varies diurnally in rice.