Soil physical conditions affecting seedling root growth

Abstract

The lengths, fresh weights, and dry weights of pea seedling roots grown for 48 hours in loose-soil columns were progressively less as oxygen partial pressures of the soil atmosphere varied from 0.16 to 0 atm. The roots were thicker at intermediate oxygen levels than in either 0 or 0.21 atm oxygen. The number of vacuolated cells per root were the same in 0.21 and 0.08 atm oxygen indicating that rate of cell division was the same. Therefore over this range decrease in cell elongation and increased cell breadth were responsible for the shorter, thicker roots. Rate of cell division was reduced at 0.03 atm oxygen. The utilisation of the seedling metabolite decreased from 0.10 to 0.03 atm oxygen and the hyperbolic relationship for oxygen uptake by excised pea roots suggests a causal relationship between growth, cell development, and oxygen availability. On this assumption pea root elongation was calibrated at different mechanical impedance and oxygen levels in order to predict the oxygen concentration at the surface of pea roots growing in poorly aerated soils.