Closed system O-2 uptake: a simple technique of nodule oxygen permeability estimation

Regulation of nitrogen fixation in response to various environmental conditions often involves an adjustment in nodule permeability and, because of the importance of nodule permeability in nitrogen fixation, several methods to estimate it have been developed, In the present study, these methods are reviewed and their limitations are highlighted, A simple, rapid and inexpensive technique that can be used to estimate permeability of nodules and respiration of other plant tissues is described, The technique was evaluated by comparing it to the lag-phase technique as an independent and reliable method for estimating nodule permeability, Over a wide range of nodule permeability estimates, the closed system O-2 uptake technique was linearly related to lag-phase permeability estimates. The technique was tested further by studying the response to sub- and supra-ambient pO(2) in the root environment, and the responses agreed well with published reports on the effect of O-2 on nodule permeability, The technique was found to be very satisfactory in estimating nodule permeability and may be used to measure the ability of other plant tissues to take up O-2.