B. BAR-YOSEF - Institute of Soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
J.R. LAMBERT - Institute of Soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Corn and cotton plants were grown in nutrient solution in acrylic containers constructed of two co-axial cylinders, the annular volume of which was partitioned into six compartments. The root system of a single plant located in the internal cylinder was divided into the compartments, where the solutions differed in osmotic potential, oxygen concentration or nitrate concentration. Root length (L) in each compartment was measured as a function of growth time (t) to study the validity of equation (1) for the various parts of the root system and to determine the relationship between GRC (the specific root growth rate) and the concentration of each of the three variables in the solution.
dL/dt = GRC·L (1)
Evidence is presented for the validity of equation (1) for the growth of various parts of the root system during 20 to 25 days.
While equation (1) held, GRC was affected by the different environmental factors, varying between 0.1 and 0.6 day-1. Nitrate concentration in the range of 0 to 30 meq/liter had little effect on GRC at 24°C, but an increase in GRC with increasing nitrate concentration was observed at a temperature of 35°C.
Increasing the dissolved O2 concentration from 5 to 25 ppm increased GRC, but the response diminished above 10 ppm O2. A difference between GRC of a split and a whole root system was observed only in different osmotic potentials induced by adding carbowax. While in a split root system the minimum GRC was obtained for roots found at a potential of 1.6 bars, whole corn roots showed an almost continuous, though moderate decrease in GRC when the osmotic potential increased from that in the control solution to about 5 bars.
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