Changes in stubble carbohydrate content during regrowth of defoliated perennial ryegrass (Lolium perenne L.) on two nitrogen levels

Changes in stubble carbohydrate content during the regrowth of ryegrass (Lolium perenne L.) grown under hydroponic conditions at two nitrogen levels were studied as a function of time by high-performance liquid chromatography. Experimental data showed that regrowth at a non-limiting nitrogen level (1·0 mol m−3 NH4NO3) involved two different physiological periods. The first occurred during the first 6 d and was characterized by the mobilization of 60 to 90% of the soluble carbohydrates (i.e. glucose, fructose, sucrose, oligofructans and polyfructans). During the second period (6.28 d of regrowth) carbohydrate contents rose to the values observed prior to cutting (20% of dry matter at the 28th d of regrowth). The effect of low nitrogen conditions (0·2 mol m−3 NH4NO3) was observed only during the second phase. Plants regrown in a nitrogen-starved medium accumulated 2·3-fold more polyfructans than plants regrown in a non-limiting nitrogen medium. Their fructose and glucose contents remained at 2% of dry matter from the end of the first phase of mobilization. The experimental results are interpreted and discussed in terms of the existence of two distinct fructan synthetic pathways.