title: Cold acclimation in warmer extended autumns impairs freezing tolerance of perennial ryegrass (Lolium perenne) and timothy (Phleum pratense).
abstract: The effect of variable autumn temperatures in combination with decreasing irradiance and daylength on photosynthesis, growth cessation and freezing tolerance was investigated in northern- and southern-adapted populations of perennial ryegrass (Lolium perenne) and timothy (Phleum pratense) intended for use in regions at northern high latitudes. Plants were subjected to three different acclimation temperatures; 12, 6 and 9/3°C (day/night) for 4 weeks, followed by 1 week of cold acclimation at 2°C under natural light conditions. This experimental setup was repeated at three different periods during autumn with decreasing sums of irradiance and daylengths. Photoacclimation, leaf elongation and freezing tolerance were studied. The results showed that plants cold acclimated during the period with lowest irradiance and shortest day had lowest freezing tolerance, lowest photosynthetic activity, longest leaves and least biomass production. Higher acclimation temperature (12°C) resulted in lower freezing tolerance, lower photosynthetic activity, faster leaf elongation rate and higher biomass compared with the other temperatures. Photochemical mechanisms were predominant in photoacclimation. The northern-adapted populations had a better freezing tolerance than the southern-adapted except when grown during the late autumn period and at the highest temperature; then there were no differences between the populations. Our results indicate that the projected climate change in the north may reduce freezing tolerance in grasses as acclimation will take place at higher temperatures and shorter daylengths with lower irradiance.
authors.affiliation: Department of Grassland and Livestock, Norwegian Institute of Bioeconomy Research, Holt, 9016 Tromsø, Norway.|Department of Plant Sciences, Faculty of Biosciences, Norwegian University of Life Sciences, 1432, Ås.
authors.forename: Sigridur
authors.initials: S
authors.lastname: Dalmannsdottir
authors.affiliation: Department of Grassland and Livestock, Norwegian Institute of Bioeconomy Research, Holt, 9016 Tromsø, Norway.
authors.forename: Marit
authors.initials: M
authors.lastname: Jørgensen
authors.affiliation: Department of Plant Physiology, University of Agriculture in Krakow, 30-239, Krakow, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Rapacz
authors.affiliation: Department of Grassland and Livestock, Norwegian Institute of Bioeconomy Research, Fureneset, 6967, Hellevik i Fjaler, Norway.
authors.forename: Liv
authors.initials: L
authors.lastname: Østrem
authors.affiliation: Graminor AS, Bjørke gård, Hommelstadvegen 60, 2322, Ridabu, Norway.
authors.forename: Arild
authors.initials: A
authors.lastname: Larsen
authors.affiliation: Department of Grassland and Livestock, Norwegian Institute of Bioeconomy Research, Holt, 9016 Tromsø, Norway.|Faculty of Bioscience, Fisheries and Economics, UiT - The Arctic University of Norway, Tromsø, 9037, Norway.
authors.forename: Rolf
authors.initials: R
authors.lastname: Rødven
authors.affiliation: Department of Plant Sciences, Faculty of Biosciences, Norwegian University of Life Sciences, 1432, Ås.
authors.forename: Odd Arne
authors.initials: OA
authors.lastname: Rognli
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D003080:Cold Temperature; D005615:Freezing; D018506:Gene Expression Regulation, Plant; D008129:Lolium / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D031784:Phleum / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins