The Effects of Seasonality and Waterlogging on the Root Systems of a Number of Hakea Species

Abstract

Proteoid and non-proteoid roots are produced only during winter-spring under the Mediterranean climatic conditions of south-western Australia. However, dormant roots can be induced to form new root structures in summer, if sufficient water is applied to that part of the root system. The seasonal occurrence of proteoid roots is therefore due to the annual variation in water available for growth of the surface parent roots. Both proteoid and non-proteoid root growth increase as water availability is increased from the permanent wilting point to one to two times field capacity, with a trebling in the proportion of proteoid roots by weight in the root system. This is followed by a steep decline in total root weight and in the proportion of proteoid roots in the root system as water availability is increased from two to three times field capacity. While the size of proteoid roots is greatest under non-waterlogged conditions (redox potential of 450-550 mV), their number per unit total root weight is greatest under moderately waterlogged conditions (redox potential of 120-350 mV).