Fixation of Dinitrogen-15 Associated with Rice Plants

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Rice plants (IR26 and Latisail) obtained at near heading stage from a wetland field were transferred to water culture and exposed to 15N2 in a gas-tight growth chamber for 7 days to measure N2-fixing activities associated with the rice. The activities measured varied from 6.5 to 11.6 μmol of N2 fixed per hill per day. The outer leaf sheath had about 2.5 times higher N2-fixing activities per unit weight than the root. Slight activities were also found in the basal node and inner leaf sheath. Wrapping basal parts of the stem with aluminum foil did not decrease the activities of N2 fixation in these parts. Thus, the outer leaf sheath as well as the root are N2-fixing sites in rice plants. N2 fixation found in above-ground parts is not due to photoautotrophic organisms. Less than 10% of the fixed nitrogen was translocated from the fixing sites to the leaf blades and the young panicles.

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