Morin, C., Bélanger, G., Tremblay, G. F., Bertrand, A., Castonguay, Y., Drapeau, R., Michaud, R., Berthiaume, R. and Allard, G. 2012. Short Communication: Diurnal variations of nonstructural carbohydrates and nutritive value in timothy. Can. J. Plant Sci. 92: 883–887. Nonstructural carbohydrate (NSC) concentration in timothy (Phleum pratense L.) increased during the day by 16 to 41 g kg−1 DM (+23 to 137%) in spring and summer growth cycles and reached a maximum value between 12.8 and 13.2 h after sunrise in an area with 15 to 16 h of day length. This increase in NSC concentration was generally accompanied by a decrease in concentrations of neutral detergent fiber (−2 to 6%), acid detergent fiber (−1 to 7%), and N (−6 to 11%).

Bélanger, G., Savoie, P., Parent, G., Claessens, A., Bertrand, A., Tremblay, G. F., Massé, D., Gilbert, Y. and Babineau, D. 2012. Switchgrass silage for methane production as affected by date of harvest. Can. J. Plant Sci. 92: 1187–1197. Switchgrass (Panicum virgatum L.) is a warm-season grass recognized as a potential biomass crop for energy production in North America, but little information exists on the effect of harvest date on forage and silage characteristics of switchgrass grown in eastern Canada. Our objectives were to determine how harvest date affects several forage and silage characteristics of switchgrass and to relate these to specific methane yield from anaerobically digested switchgrass silage. Switchgrass, seeded in 2002 and 2006, was harvested and ensiled as a one-cut system on three dates in 2007: late July, early September, and early October. The regrowth from the late July harvest was also harvested in early October as a two-cut system. Silage quality parameters [pH, and concentrations of N, N-NH3, total amino acids (TAA), and volatile fatty acids (VFA)] indicated adequate fermentation of all silage samples. In a one-cut system, delaying harvest from late July to early September increased forage dry matter (DM) yield from 9.0 to 11.5 Mg ha−1, forage soluble carbohydrate (SC) concentration from 51 to 85 g kg−1 DM, and silage SC concentration from 13 to 25 g kg−1 DM; delaying harvest from late July to early October decreased forage in vitro true digestibility (IVTD) from 720 to 582 g kg−1 DM, forage in vitro digestibility of the neutral detergent fibre (dNDF) from 590 to 409 g kg−1 DM, and silage acetate concentration from 7.7 to 2.6 g kg−1 DM. The regrowth had higher IVTD and dNDF, lower acid detergent fibre concentration, and higher silage lactate and acetate concentrations than a single harvest taken in early September or early October. The two-cut system and the single harvest in early September produced the highest seasonal forage DM yields (11.5 and 11.9 Mg ha−1). High specific methane yield was (i) correlated with low forage fibre concentration and high DM digestibility and (ii) more correlated to silage concentrations of lactate and acetate than to silage SC concentration.

Elevated CO2 increases soybean growth and photosynthesis, and the resulting additional supply of photosynthates stimulates nodule activity. To characterize its biochemical response to both CO2 and bradyrhizobial strains, soybean inoculated with three strains of Bradyrhizobium japonicum was grown in growth chambers under ambient (400 µmol·mol–1) or elevated (800 µmol·mol–1) CO2. Soluble sugars were generally more abundant in leaves and nodules under elevated CO2, while starch and pinitol were depleted, indicating that additional photosynthates were rapidly used, in particular for nodule growth (dry mass increased by 65%). Ureides (allantoin and allantoic acid) increased under elevated CO2 in leaves, while this increase was not significant in nodules. The indigenous strain 12NS14 induced the highest ureides concentration in nodules under elevated CO2 along with the highest nitrogenase activity and increase in shoot dry mass, indicating a positive-feedback stimulation: soybean mobilized energy reserves to support more nodules, and in return nodules synthesized more ureides to support plant growth. In contrast, the commercial strain 532c resulted in the highest ureide concentrations in leaves, coupled with the lowest nitrogenase activity and nodules yield, suggesting a feedback inhibition of nodule activity. Our results show that selection of B. japonicum strains better adapted to elevated CO2 could improve soybean performance.

The present study documents the changes in carbon and nitrogen metabolites occurring in apical buds and previous year stems of white spruce seedlings (Picea glauca [Moench] Voss) with contrasting growth phenotypes (tall vs. small) after transfer to short day (SD; 8 h) photoperiod to induce bud formation. Concentrations of total nonstructural carbohydrates markedly increased in the developing buds within the days after transfer to SD, mainly as a result of increased concentrations of monosaccharides such as glucose, fructose, and pinitol. At the same time, starch levels declined, with the resulting carbohydrates presumably used to meet early carbon requirements of the SD-induced apical bud. Concentrations of glutamine, glutamic acid and proline also decreased immediately after transfer to SD in both organs. Later stages of SDinduced bud formation were characterized by an increase in starch, sucrose, and glutamine concentrations in previous year stems, concomitant with an increase in the steady-state levels of UDP-glucose pyrophosphorylase and glutamine synthetase protein. In contrast, arginine levels increased after 2 weeks of SD exposure, indicating a transition in arginine metabolism at the time of initiation of shoot stem primordia and bud elongation. Higher accumulation of total nonstructural carbohydrates and total amino acids in previous year stems of small trees could indicate lower sink strength of apical bud during its development, which could in turn impact subsequent tree growth.Résumé : La présente étude présente les changements se produisant au niveau des métabolites carbonés et azotés dans le bourgeon terminal et la tige de l'année précédente d'épinettes blanches (Picea glauca [Moench] Voss) ayant des phénotypes de croissance contrastés (petits versus grands arbres), après avoir été transférées en conditions de jours courts (JC ; 8 heures) de manière à induire la formation des bourgeons. Les concentrations en hydrates de carbone non structuraux augmentent de manière marquée dans les bourgeons en développement immédiatement après le transfert en JC, principalement en raison de l'augmentation des concentrations en monosaccharides tels que le glucose, le fructose et le pinitol. Au même moment, les niveaux d'amidon diminuent en faveur de l'augmentation des sucres solubles indispensables à la demande en carbone reliée à formation des bourgeons terminaux induite en JC. Les concentrations en glutamine, acide glutamique et proline diminuent également immédiatement après le transfert des épinettes en JC dans les deux organes. Les stades plus avancés de la formation des bourgeons terminaux induite en JC sont caractérisés par une augmentation des concentrations en amidon, en saccharose et en glutamine dans les tiges de l'année précédente, en concomitance avec une augmentation des niveaux d'UDPglucose pyrophosphorylase et de glutamine synthase. En revanche, les concentrations en arginine augmentent après 2 semaines d'exposition aux JC, suggérant qu'une transition au niveau du métabolisme de l'arginine se produit...