ABSCISIC-ACID IN SOILS - WHAT IS ITS FUNCTION AND WHICH FACTORS AND MECHANISMS INFLUENCE ITS CONCENTRATION

Abscisic acid (ABA) was detected in aqueous extracts of a range of dif ferent soils, beneath a range of crops, pasture and forest species. As suming that all the ABA is dissolved in the soil solution concentratio ns ranged from 0.6-2.8 nM. This is in the range which computer simulat ions predict is required in soils in order to prevent ABA release from the root hair zones of plant roots. The concentration of ABA in the s oil solution was highest in acid soils and in soils with reduced moist ure, and was lowest in moist, neutral and moderately alkaline soils. A BA in the soil solution of maize fields increased during the vegetativ e period. After incubation in soil for 72 h, radioactive ABA was degra ded by 30-40%. Tetcyclacis, an inhibitor of the oxidative breakdown of ABA, completely prevented the degradation of ABA in the soil solution . Acid conditions and high salt concentrations significantly retarded ABA breakdown.