Simultaneous Measurement of Acetylene Reduction and Respiratory Gas Exchange of Attached Root Nodules

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Abstract
A method was developed for the simultaneous measurement of acetylene reduction, CO2 evolution and O2 uptake by individual root nodules [inoculated with Frankia sp.] of intact N2-fixing plants (Alnus rubra Bong.). The nodules were enclosed in a temperature-controlled leak-tight cuvette. Assay gas mixtures were passed through the cuvette at a constant, known flow rate and gas exchange was measured by the difference between inlet and outlet gas compositions. Gas concentrations were assayed by a combination of an automated gas chromatograph and a programmable electronic integrator. CO2 and ethylene evolution were determined with a coefficient of variation which was < 2%, whereas the coefficient of variation for O2 uptake measurements was < 5%. Nodules subjected to repeated removal from and reinsertion into the cuvette and to long exposures of 10% vol/vol acetylene showed no irreversible decline in respiration or acetylene reduction. This system offers long-term stability and freedom from disturbance artifacts plus the ability to monitor continuously, rapidly and specifically the changes in root nodule activity caused by environmental perturbation.