Regrowth Kinetics of Dactylis glomerata Following Root Excision

The growth kinetics of Dactylis glomerata following a root excision were studied in order to characterize the process of partitioning of carbon assimilates between shoots and roots. Plants were grown hydroponically, in constant environments. The variations with time of shoot and root fresh weights during regrowth were measured using a nondestructive method. The effect of root excision on shoot and root water contents was also determined from complementary experiments. Immediately after cutting, the specific growth rate increased markedly for roots and decreased slightly for shoots, but this decrease can be at least partly accounted for by the variation of the shoot water content. At the end of the perturbed phase, the specific growth rates and the root fraction had almost returned to the values measured immediately before cutting. The experimental regrowth kinetics were analysed in terms of a kinetic model which calculates shoot and root growth as the difference between the carbon provided by photosynthesi s and carbon losses associated with respiration. A satisfactory description of the regrowth kinetics was obtained by assuming that the partitioning of carbon substrates between shoots and roots is not modified by cutting, and that the partitioning coefficient remains constant during regrowth. According to this analysis, the stimulation of root growth after cutting can be mainly attributed to the reduction in the part of carbon substrates utilized in roots for maintenance requirements.