gen, lead to increasingly poor recovery and even death in various grass species, regardless of the most favourable An experiment was designed to evaluate the role of climatic and soil environment (Davies, 1965; Richards, N and C reserves on regrowth of Lolium perenne cv. 1993). Bravo following defoliation. By using two nitrogen fert- Growth following defoliation depends first of all on ilization levels together with three photoperiodic con- the development of a photosynthetic surface (Richards, ditions, plants with variable contents of water-soluble 1993). A critical role of carbohydrate and N reserves as carbohydrates (43‐216 mg g’1 DW in stubble) and substrates for refoliation has been advocated long ago contrasting amounts of nitrogen (7‐49 mg g’1 DW) (Graber et al., 1927; Sullivan and Sprague, 1943). The were obtained. Plants were severely defoliated and hypothesis has been advanced that ‘new top growths are regrowth was followed for 28 d under the same envir- initiated and developed largely at the expense of previonmental conditions. The yield of leaf dry matter at ously accumulated organic reserves, and that their quantthe end of the regrowth period was not related to the ity and availability limit the amount of growth that will initial level of carbohydrate reserves. However, levels occur’ (Graber et al., 1927). Indeed, extensive mobilizaof fructan in leaf sheaths and in elongating leaf bases tion of non-structural carbohydrates and nitrogenous strongly influenced the shoot yield during the first 2 d compounds (Alberda, 1957; Volenec, 1986; Ourry et al., following defoliation. Fructan exohydrolase activity 1989; Prud’homme et al., 1992) occurred in the residual increased 2‐3-fold in sheaths and 3.5‐5-fold in elong- parts of defoliated plants. However, it has been pointed ating leaf bases, suggesting that not only fructans from out that a decrease in the amount of non-structural sheaths but also fructans from immature cells may be carbohydrates did not necessarily imply a causal role for used as substrates for growth. In contrast, no direct these reserves in initiating and aVecting regrowth (May, relationship was found between shoot production and 1960). In experiments in which the level of carbohydrates nitrogen or soluble protein accumulation in source have been modified by short-term exposures to darkness organs during early regrowth. A significant correlation and raised temperatures, it has been shown that the yield existed with the initial amount of soluble proteins in of leaf material after cutting was related to the percentage sheaths and in elongating leaf bases after only 6 d of of soluble carbohydrates in the stubble at the time of regrowth. cutting and that once growth was fully established, the rate became independent of the pretreatments applied