Was shoot growth rate determined by root soluble N reserve content or VSP concentration?
The correlations between N reserves and shoot growth reported in this study were confirmed by previous results obtained under field conditions. In a field experiment where variations in N and C reserve levels were induced by genetics or variation in crop management, Avice et al. reported that shoot regrowth was linearly related to both taproot soluble protein and VSP contents on the day of defoliation (Avice et al., 1997b). By contrast, no relationship was detected between shoot regrowth and initial starch or N taproot contents. These authors suggested that root protein and VSP are key organic reserves for alfalfa shoot regrowth after cutting; nevertheless they did not determine the relative importance of soluble protein versus VSP reserves on shoot regrowth. In order to increase the soluble protein pool, alfalfa plants could increase root biomass, the concentration of root proteins (especially VSP) without changing RDM, or increase both factors. In this experiment and others (Avice et
