The Effect of Temperature on N₂Fixation (C₂H₂Reduction) by Nodules of Legume and Actinomycete-Nodulated Woody Species

Abstract

The effect of temperature on C2H2 reduction by excised root nodules of legume and actinomycete-nodulated woody species was investigated. Nodules were incubated at temperatures from 2 to 44 C, exposed to C2H2 for 1 h, and sampled for C2H4. A surge of activity by nodules of Elaeagnus umbellata Thunb. occurred between 8 and 11 C with maximum activity at 34-36 C. The C2H2 reduction rapidly declined at temperatures above the maximum and stopped at 43 C. Nodules subjected to 0.6 C recovered nitrogenase activity within 1 h when temperature was raised to 27 C, whereas loss of activity was irreversible to 45 C. The activation temperature of Shepherdia argentea Nutt., Robinia pseudoacacia L., Robinia fertilis Ashe. `Arnot,' and Myrica pensylvanica Lois. occurred within a range of 7-10 C, whereas that of Caragana arborescens Lam. was at 3-5 C. The activation point for linear increases in C2H2 reduction may be due to phase changes. The Arrhenius plot for E. umbellata shows a change in activation energy at 9.5 C. The efflux of 3H2O by nodules of E. umbellata was affected by temperature and was greater at 10.5 than at 6.1 C. Greater leakage of total electrolytes from nodules of M. pensylvanica occurred at 20 C than at 2 C.