Nodulation and N2-fixation by Calliandra calothyrsus and Sesbania sesban grown at different root temperatures

Calliandra calothyrsus and Sesbania sesban were grown in controlled environment cabinets at range of controlled root and shoot temperatures. For C. calothyrsus nodulation was delayed until 13 days after inoculation at 20 and 24°C and no nodules formed at 40°C. Nodules formed most rapidly at 28 and 32°C, and were visible by 10 days. S. sesban nodulated earlier than C. calothyrsus. Nodules were formed by 6 days after inoculation at 28–36°C but at 20°C were delayed until 10 days. Remarkably, nodulation still occurred at a root temperature of 40°C. S. sesban was also grown at a root temperature of 32-28°C (day-night) for 3 wk before being transferred to root temperatures of 22-18°C, 32-28°C, 36-32°C and 40-36°C (day-night). The maximum shoot dry mass occurred with day root temperatures of 32 and 36°C. Shoot and nodule dry mass declined significantly at 40°C, but nitrogenase activity was still present 4 wk after transfer.