Physical Environment and Symbiotic Nitrogen Fixation. IV. Faotors Affecting the Early Stages of Nodulation

Abstract

The influence of root temperature on the initial nodulation of Trifolium subterraneum L. was examined, and observations were made on the effect of light period and shoot temperature on this character. The maximum constant root temperature at which nodules would form was 33�0, and the minimum was in the vicinity of 7�0. The most rapid initial nodulation (2-3 days after inoculation) was observed at 30�0, and plants growing at this temperature had the highest rate of nodule appearance. Below 22�0, there was a marked increase in the "time to first visible nodule" and a general decline in the rate at which they appeared. Differences were observed in the time to first visible nodule, and in the rate of nodule appearance, between different cultivars of T. 8ubterraneum. There was an indication of a temperature X cultivar interaction for these characters. With the three strains of Rh. trifolii used, no differences in their ability to form nodules were observed, although it was known that their subsequent symbiotic behaviour differed under certain root temperature conditions.