REDUCTION OF ACETYLENE BY NODULES OF TRIFOLIUM SUBTERRANEUM AS AFFECTED BY ROOT TEMPERATURE, RHIZOBIUM STRAIN AND HOST CULTIVAR

The nitrogenase activity (measured by reduction of C2H2 to C2H4) of nodules of Trifolium subterraneum grown at root temperatures from 7°C-19°C was broadly correlated with nitrogen fixation. Root temperature did not affect enzyme activity per se but did affect the amount of enzyme formed. Exposure of nodules to 7°C for 24 h did not decrease activity cf. 19°C. Activity was greatest when nodules were about 4 days old, before swollen bacteroid forms were produced, and then declined. The effectiveness of a bacterial strain at a given temperature was related to the amount of enzyme produced and to its persistence. Nitrogenase activity should be measured throughout the plant growth cycle for valid comparisons of strain effectiveness. © 1969 Springer-Verlag.