Frankia growth and activity as influenced by water potential

Growth responses of Frankia isolates to decreasing water potential were monitored in systems where potentials were controlled by KCl, NaCl and Polyethylene glycol. The highest potential tested was — 2 bar (basal medium). The general pattern emerging was that isolates from Alnus glutinosa, A. viridis and Comptonia peregrina showed declining growth at potentials below — 2 to — 5 bar. A Myrica gale isolate showed declining growth with decreasing potential. All isolates were more sensitive to decreases in potential in a matric controlled than an osmotic controlled system. They all showed approximately 50 percent growth reduction at — 5 to — 8 bar, and meagre growth at — 16 bar after 35 days. The Comptonia isolate was the most vigorous at low potentials. Nitrogen fixation ability was monitored for two isolates. Highest specific activities were observed between — 3 and — 5 bar for the Myrica isolate and between — 5 and — 7.5 bar for the A. glutinosa isolate.