SOIL-WATER CONTENT, SOIL STRENGTH AND THE GROWTH OF ELM ROOT SUCKERS

The elongation rate of root suckers of Dutch elm (Ulmus x hollandica Mill.) increased with increasing age of the sucker, soil water content and net growth pressure (the excess of turgor pressure over soil restraining pressure) and it decreased with increasing soil strength. The increase in the rate of sucker elongation with age was probably the result of a decrease in osmotic potential causing an increase in the turgor pressure. Increasing soil strength increased the rate of osmotic adjustment. The increase in the rate of sucker elongation with increasing soil water content was probably due to an increase in the water potential of the sucker and a decrease in soil strength associated with increasing soil water content.