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MATERIALS AND METHODS Grazing animals prefer some plants to others. These choices are Cultivars and Experimental Design likely related to physical and chemical factors such as energy-dense The eight endophyte-free tall fescue cultivars included in carbohydrates contained in plants. This study quantified the nonstructhis study were 'Barcel', 'Kenhy', 'Kentucky-31' (KY-31), tural carbohydrate fractions in each of eight vegetatively growing, 'Missouri-96' (MO-96), 'Mozark', 'Stargrazer', and the experiendophyte-free, tall fescue cultivars (Festuca arundinacea Schreb.) mental selections C-1 and HiMag (Mayland and Sleper, 1993). and relates their sugar concentrations to cattle grazing preferences. On 20 Sept. 1991, these grasses were seeded in rows into The experimental area consisted of eight cultivar plots replicated three an irrigated, Portneuf silt loam loess soil (Durinodic Xeric times in each of three pastures. Within each pasture, forage was Haplocalcid) near Kimberly, in south-central Idaho (42Њ30Ј sampled between 0830 and 1000 h mountain daylight time (MDT) N, 114Њ08Ј W, elevation 1200 m). The experimental design during each of four seasons and 2 yr. Freeze-dried forage samples was a randomized complete block with three pastures (blocks), were extracted with hot water and an amylase (Clarase) solution. three replications nested within blocks, eight entries (main Sugars were quantified colorimetrically using potassium-ferricyanide plots), and six rows per main plot. Rows were 0.56 m apart and glucose-oxidase methods. Cattle grazing preferences among these and main plots were 3.35 by 6.7 m. tall fescue cultivars were related to the concentrations of total nonstructural carbohydrates (TNC) (r 2 ϭ 0.49, P Ͻ 0.05). Other sugar Harvesting and Sample Preparation fractions were not significantly related to grazing preference in this study. The nonstructural carbohydrate concentrations averaged over Vegetatively growing forage was clipped at a stubble height the entire study were glucose, 14; fructose, 5; sucrose, 40; fructan, 23; of 8 cm from randomly located 0.6-m sections of Rows 3 and insoluble starch, 24; and TNC, 129 g kg Ϫ1 . A forage selection criterion 4 in each plot. The forage in Block 1 was clipped on d 131, should include measures of the TNC because of their close relationship 165, 221, and 256 of 1993 and d 129, 164, 220, and 262 of 1994. to animal grazing preference.

Summary• An analysis of fructan structures, to increase the understanding of biosynthetic pathways and enzymology of fructan synthesis in root and leaf tissues of Lolium perenne is reported.• Fructan extracted from stubble of L. perenne plants was analyzed by high performance anion exchange chromatography and pulsed amperometric detection (HPAEC-PAD) using a new desalting technique. Structures of fructan isomers, separated up to DP16 (DP, degree of polymerization), were established by chromatographic elution times or by GC-MS.• Fructans of DP8 belonged essentially to three series: inulin series, inulin neoseries and the levan neoseries, which is/are different in glucose (terminal or internal) and linked fructose residues. High DP fructans (DP > 8) comprised 75% molecules with an internal glucose residue. They had some branch points although 1 and 6 kestotetraose could not be detected and the β (2 -6) linked fructose residues were 70 times more abundant than the β (2 -1) linked fructose residues. Roots, sheaths, leaf blades and elongating leaves accumulated similar fructans although amounts of both low and high, and types of low, DP fructans, differed.• It is proposed that fructans in L. perenne are synthesized via four enzymes: 1-SST (1-sucrose-sucrosefructosyl transferase), 1-FFT (1-fructan-fructanfructosyl transferase), 6G-FT (6-glucose-fructosyl transferase) and 6-FFT (6-fructanfructanfructosyl transferase) or 6-SFT (6-sucrose-fructanfructosyl transferase).

The savannas (cerrado) of south-central Brazil are currently subjected to frequent anthropogenic burning, causing widespread reduction in tree density. Increasing concentrations of atmospheric CO could reduce the impact of such frequent burning by increasing the availability of nonstructural carbohydrate, which is necessary for resprouting. We tested the hypotheses that elevated CO stimulates resprouting and accelerates replenishment of carbohydrate reserves. Using a factorial experiment, seedlings of a common Brazilian savanna tree, Keilmeyera coriacea, were grown at 350 ppm and 700 ppm CO and at two nutrient levels. To simulate burning, the plants were either clipped at 15 weeks or were left unclipped. Among unclipped plants, CO and nutrients both stimulated growth, with no significant interaction between nutrient and CO effects. Among clipped plants, both CO and nutrients stimulated resprouting. However, there was a strong interaction between CO and nutrient effects, with CO having a significant effect only in the presence of high nutrient availability. Under elevated CO, carbohydrate reserves remained at higher levels following clipping. Root total nonstructural carbohydrate remained above 36% in all treatments, so carbohydrate reserves did not limit regrowth. These results indicate that under elevated CO this species may be better able to endure the high frequency of anthropogenic burning in the Brazilian savannas.