Regrowth Kinetics of Dactylis glomerata Following Root Excision

Abstract

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 photosynthesis 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.

Clothing the Emperor: Dynamic Root–Shoot Allocation Trajectories in Relation to Whole-Plant Growth Rate and in Response to Temperature

“…For example, the species we used in this experiment are common in many grazed habitats in the British Isles, so it would be useful to know how their growth and allocation trajectories might respond to defoliation. This could be done by assuming the almost complete removal of shoot biomass at a certain time ( S → 0) then plotting regrowth trajectories with the same or different r and Y max values as controls (although, in the case of defoliation, Equation (1) would need to be modified because regrowth, fuelled by the consumption of stored assimilates, tends to follow monomolecular rather than logistic trajectories [17,18,43]).…”

“…Often, no temporal information about allocation is collected, so it is not always clear what constitutes ontogenetic drift in allocation as distinct from a genuine response. But if some plants are subjected to a specific treatment at a defined time, and if growth is measured repeatedly before and after that change, and compared with controls, it is possible to say definitively if allocation responds to that treatment; temporal changes in allocation in control plants then reflect ontogenetic drift [16,17,18,19,20,21,22]. A biomass allocation response to the environment can occur only if there is a differential change in rates of biomass production between root and shoot [1].…”