Ráðunautafundur - 15.02.2002, Blaðsíða 280

278
Tognetti o.fl. 1990). Sykrusöfnun sem tengist flutningi grasanna frá hærri hita til lægri getur
einnig tengst minna næmi ljóstillífunar en vaxtarferla fyrir hitastigslækkun (Levitt 1980,
Wagner o.fl. 1983).
Hugsanlega er meginhlutverk frúktananna að virka sem geymsluform fyrir kolefni á
tímabilum tímabundins offramboðs ljóstillífunarafurða. Á þessum forsendum má gera ráð
fyrir að æskilegt sé ffá gæðasjónarmiði að uppskera grösin á svölum dögum frernur en hlýjum
og fremur að kvöldi en morgni (Fisher o.fl. 1999). í þessu efni getur verið marktækur munur á
grasstofnum.
ÞAKKIR
Phil A. Harrison og N. Jerry Chatterton við USDA Agricultural Research Service, Forage and Range Research
Laboratory, Utah State University, Logan, UT 84322-6300, USA fá bestu þakkir fyrir aðstoð og aðstöðu við
vinnu þessa rannsóknarverkefnis, sem fór fram í Logan vorið og sumarið 2000.
HEIMILDIR
Chatterton, N.J. & Harrison, P.A., 1997. Fructan oligomers in Poa ampla. New Phytologisl 136: 3-10.
Chatterton, N.J., Harrison, P.A., Bennett, J.H. & Asay, K.H., 1989. Carbohydrate partitioning in 185 accessions
of Gramineae grown under warm and cool temperatures. Journal of Plant Physiology 134: 169-179.
Fisher, D.S., Mayland, H.F. & Bums, J.C., 1999. Variation in ruminant's preference for tall fescue hays cut at
sundown or sunup. Journal of Animal Science 77: 762-768.
Gudmundsson, B. & Thorsteinsson, B., 1999. The effect of wilting and ammonium tetraformiat (ATF) additive
on big bale second cut grass fermentation and subsequent lamb feeding intake and performance í: Proceedings
of the Xllth International Silage Conferenc, July 5-9, Uppsala, Sweden (ritstj. Pauli, T.), 183-184. ISBN 91 576
5678 9.
Levitt, ]., 1980. Plants Response to Environmenta! Stresses. Vol 1.2. útg. Academic Press, New York
Pollock, C.J., 1981. Pattems of tumover fructans in leaves of Dactylis glomerata L. New Phytologist 90: 645-
650.
Pollock, C.J., 1986. Fructans and the metabolism of sucrose in vascular plants. New Phytologist 104:1-24.
Pollock, C.J. & Caims, A.J., 1991. Fructan metabolism in grasses and cereals. Annual Review of Plant Physio-
logy and Plant Molecular Biology 42: 77-101.
Smith, D., 1973. The nonstructural carbohydrates. í: Chemistry and Biochemistry of Herhage, (ritstj. Butler,
G.W. & Bailey, R.W). Academic Press, 105-155.
Suzuki, M. & Nass, H.G., 1988. Fructan in winter wheat, triticale and fall rye cultivars of varying cold hardi-
ness. Canadian Journal of Botany 66: 1723-1728.
Thorsteinsson, B., Gudmundsson, B. & Brynjolfsson, R., 1996.Grass carbohydrates and silage quality. í: Pro-
ceedings of the XI International Silage Conference Aberystwyth (ritstj. Jones o.fl.), 50-51. ISBN 0 7084 0573 8
Thorsteinsson, B. & Tillberg, J.-E., 1990. Changes in photosynthesis/respiration ratio and levels of few
carbohydrates in leaves of nutrient depleted barley and pea. Journal of Plant Physiology 136: 532-537.
Tognetti, J.A., Salemo, G.L. & Crespi, M.D., 1990. Sucrose and frnctan metabolism of different wheat cultivars
at chilling temperatures. Physiologia Plantarum 78: 554-559.
Wagner, W., Keller, F. & Wiemken, A., 1983. Fructan metabolism in cereals: Induction in leaves and compart-
mentation in protoplasts and vacuoles. Zeitschrift fur Pflanzenphysiologie 112: 359-372.