Development of actinomycetes in brown semidesert soil under low water pressure

Under laboratory conditions, the spores of a xerotolerant Streptomyces odorifera strain germinated in brown semidesert soil even at extremely low soil water pressure (P = -96.4 MPa, -964 atm, a (w) 0.50); the plantlets increased in length and formed mycelium, on which a new generation of spores was produced (a complete development cycle of the actinomycetes-from a spore to the formation of new spores-passed). The duration of the first cycles of the actinomycetes' development varied from 13 days at P = -27 atm to 57 days at P = -964 atm and was directly proportional to the absolute value of the soil water pressure (P). In the first cycles of the actinomycetes' development, the rate of increase of the concentration of the germinated spores and mycelium, as well as the logarithms of the mycelium-to-germinated spore concentration ratios, was inversely proportional to the logarithm of P. These relationships indicated that the energy state of the water determined its availability to soil biota and, hence, the activity of its physiological and biochemical processes.