Relative Death Rate: A Dynamic Parameter Describing Plant Response to Stress

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Abstract
Senescence and death of plant parts are frequently accelerated by various stresses to which plants are subjected. The dynamics of these responses can be investigated by determining the parameter, relative death rate, Rd, defined as the rate of increase in senescent or dead material as a function of the amount of living tissue present. By curve-fitting procedures, instantaneous values of Rd may be determined. Examples taken from the literature illustrate the derivation and changes with time of Rd for Vicia faba under water stress, Lolium perenne and L. multiflorum mixtures with or without the application of N-fertilizer and Agropyron smithii subjected to long-term treatment with SO2 pollution. These examples illustrate the range of primary data which may be used to determine Ra, e.g., numbers of live and dead leaves per plant, weights of live and dead leaves per unit ground area, and live and dead areas of a particular leaf. Mean relative death rates, Ra, over discrete time intervals may be calculated from algebraically derived equations, and may provide a useful measure of plant response to environmental stresses.