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Root and Nodule Respiration in Relation to Acetylene Reduction in Intact Nodulated Peas ¹

^a Prairie Regional Laboratory, National Research Council of Canada, Saskatoon, Saskatchewan, Canada S7N OW9

Inoculated pea plants (Pisum sativum L.) were grown with N-free nutrients in a controlled environment room and rates of respiratory CO₂ evolution and C₂H₂ reduction by the intact nodulated roots were determined. Experiments followed changes related to diurnal cycles, light and dark treatments, partial defoliation, aging of plants and NH₄NO₃ addition. In all experiments, changes in C₂H₂ reduction were associated with parallel changes in the respiration rate, although in all but the defoliation experiment there was a basal level of respiration which was independent of the rate of C₂H₂ reduction. In conditions which affected growth or plant size as well as C₂H₂ reduction, respiration changed by an average of 0.42 mg CO₂ (µmol C₂H₂ reduced)^–1. However, some treatments decreased C₂H₂ reduction without greatly changing the growth and in these conditions respiration was decreased by an average of 0.27 mg CO₂ (µmol C₂H₂ reduced)^–1. While this value may also include some respiration associated with other processes, it is proposed that it more closely estimates respiration directly associated with energy utilization for acetylene reduction; whereas the higher value includes respiration related to maintenance and growth processes as well.