Nitrogen fixation and denitrification in the roots of flooded crops

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Abstract
N2-fixing and denitrifying activities in excised roots of four flooded crops, rice, arrowhead, Job's tear and rush were determined. The highest rate of N2-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· dry root-1, respectively. The lowest rate among the four crops was observed in the roots of Job's tear, whieh 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 N2-fixation and denitrification in the flooded roots of these crops. Two to four N2-fixing bacteria were isolated from each crop root. Isolates from riee showed higher activity under microaerophilic conditions than aerobic conditions. From other crops, different types of isolates which showed higher activity under aerobic conditions than mieroaerophilic conditions were identified.