NITROGEN FIXATION AND DENITRIFICATION IN THE ROOTS OF FLOODED CROPS

概要

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N_2-fixing and denitrifying activities in excised roots of four flooded crops, rice, arrow-head, Job's tear and rush were determined. the highest rate of N_2-fixing activity determined by the acetylene reduction method was observed in the roots of arrowhead with 4.9 μg N・hr^<-1>・g dry root^<-1>. Activities in rice and Job's tear, were 1.9, 1.2 μg N・hr^<-1>・g dry root^<-1>, respectively. The lowest rate was observed in rush with 0.27 μg N・hr^<-1>・g dry root^<-1>. Rates of denitrifying activity determined by the acetylene inhibition method in the roots of rice, rush and arrowhead were 4.8, 4.7 and 5.0 μg N・hr^<-1>・g dry root^<-1>, respectively. The lowest rate among the four crops was observed in the roots of Job's tear, which amounted to 0.9 μg N・hr^<-1>・g dry root^<-1>. It appears that there was no correlation between the rate of activity and the number of bacteria during the process of N_2-fixation and denitrification in the flooded roots of these crops. Two to four N_2-fixing bacteria were isolated from each crop root. Isolates from rice showed higher activity under microaerophilic conditions than aerobic conditions. From other crops, different types of isolates which showed higher activity under aerobic conditions than microaerophilic conditions were identified.
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