Time course of acetylene reduction in nodules of five actinorhizal genera.

The rate of acetylene reduction was measured as a function of time after addition of 10% acetylene in Alnus, Casuarina, Ceanothus, Datisca, and Myrica. The maximum rate occurred after 45 to 60 seconds and was maintained for an additional 0.5 to 4 minutes before a decline in rate to 30 to 90% of the maximum. The rate then recovered to a value of 63 to 98% of the maximum. Removal of the shoot and lower roots did not affect nodule activity.