Root Respiration Associated with Nitrogenase Activity (C2H2) of Soybean, and a Comparison of Estimates

Root respiration associated with symbiotic fixation in soybean (Glycine max [L.] Merr.) was estimated by four methods.Averaged over the life of the plant, the root respires 5.8 milligrams C per milligram N accumulated from fixation. When nitrogenase (C(2)H(2)) activity and root respiration were decreased by treating roots briefly with 1.0 atmosphere O(2), the respiration associated with nitrogenase was estimated as 2.10 micromoles CO(2) per micromole C(2)H(4).When nitrogenase activity and respiration were decreased by addition of nitrate, the respiration associated with fixation was calculated as 2.90 micromoles CO(2) per micromole C(2)H(4). Removing nodules from roots decreased fixation and root respiration, and the ratio was 4.08 micromoles CO(2) per micromole C(2)H(4). When soybean plants were kept in prolonged darkness, then returned to light, the associated drop and recovery of respiration and nitrogenase activity had a ratio of 4.36 micromoles CO(2) per micromole C(2)H(2).