title: Soil temperature and intermittent frost modulate the rate of recovery of photosynthesis in Scots pine under simulated spring conditions.
abstract: An earlier onset of photosynthesis in spring for boreal forest trees is predicted as the climate warms, yet the importance of soil vs air temperatures for spring recovery remains to be determined. Effects of various soil- and air-temperature conditions on spring recovery of photosynthesis in Scots pine (Pinus sylvestris) seedlings were assessed under controlled environmental conditions. Using winter-acclimated seedlings, photosynthetic responses were followed after transfer to different simulated spring conditions. Recovery rates for photosynthetic electron transport and net CO(2) uptake were slower in plants from cold or frozen soil compared with controls. In addition, a greater fraction of light absorbed was not used photochemically, but was dissipated thermally via xanthophyll cycle pigments. Intermittent frost events decreased photosynthetic capacity and increased thermal energy dissipation. Within a few days after frost events, photosynthetic capacity recovered to prefrost levels. After 18 d under spring conditions, no difference in the optimum quantum yield of photosynthesis was observed between seedlings that had been exposed to intermittent frost and control plants. These results show that, if air temperatures remain favourable and spells of subfreezing air temperatures are only of short duration, intermittent frost events delay but do not severely inhibit photosynthetic recovery in evergreen conifers during spring. Cold and/or frozen soils exert much stronger inhibitory effects on the recovery process, but they do not totally inhibit it.
authors.affiliation: Max-Planck-Institut für Biogeochemie, Hans-Knöll-Straße 10, 07745 Jena, Germany.|Present address: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Golm, Germany and Institut für Forstbotanik und Baumphysiologie, Universität Freiburg, 79110 Freiburg, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Ensminger
authors.affiliation: Max-Planck-Institut für Biogeochemie, Hans-Knöll-Straße 10, 07745 Jena, Germany.
authors.forename: Lilian
authors.initials: L
authors.lastname: Schmidt
authors.affiliation: Earth and Biosphere Institute, School of Geography, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Jon
authors.initials: J
authors.lastname: Lloyd
mesh_terms: D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D005453:Fluorescence; D005615:Freezing; D020869:Gene Expression Profiling; D010788:Photosynthesis / Q000502:physiology*; D010860:Pigments, Biological; D041605:Pinus sylvestris / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012621:Seasons; D012987:Soil; D013696:Temperature; D014867:Water / Q000378:metabolism
chemical_list: D010860:Pigments, Biological; D010940:Plant Proteins; D012987:Soil; D014867:Water; D002245:Carbon Dioxide