THE ARRHENIUS EQUATION AS A MODEL FOR EXPLAINING PLANT-RESPONSES TO TEMPERATURE AND WATER STRESSES

The Arrhenius equation describes the response of biological processes to temperature. This study was conducted to examine the applicability of the Arrhenius equation to whole plant processes and to explore the application of the Arrhenius equation as a basis for characterizing plant responses to water stress. Rates of growth of leaf area and shoot dry mass of spring wheat seedlings were measured at combinations of five soil water potentials (-0.03, -0.06, -0.10, -0.17 and -0.25 MPa) and seven root temperatures (12, 14, 17, 22, 27, 29 and 32 °C). A non-linear least square procedure was used to fit the modified Arrhenius equation to experimental observations. Adequate distribution of experimental observations with respect to temperature reduces the uncertainties in parameter evaluations. The standard error of the estimate of optimum temperature for leaf area growth increased from 1.4 °C to 6.3 °C when one of the data points was omitted. The optimum temperature and the enthalpy of denaturalization of enzyme systems were independent of soil water potential. A linear relation was found between the rate constant and the activation energy:. lnka(ψ)=lnko+B(ψ)/ToThe Arrhenius equation was modified using this linear relation, leaving the activation energy as the only parameter affected by water stress. The activation energy increased linearly as soil water potential decreased, with slopes of -27.18 × 103 and -28.09 × 102 K MPa-1 for the rates of growth of leaf area and shoot dry mass, respectively. These slopes could be used as indicators of the sensitivity of plant processes to water stress. © 1990 Annals of Botany Company.