title: Photosynthetic downregulation in leaves of the Japanese white birch grown under elevated CO(2)  concentration does not change their temperature-dependent susceptibility to photoinhibition.
abstract: To determine the effects of elevated CO(2) concentration ([CO(2)]) on the temperature-dependent photosynthetic properties, we measured gas exchange and chlorophyll fluorescence at various leaf temperatures (15, 20, 25, 30, 35 and 40°C) in 1-year-old seedlings of the Japanese white birch (Betula platyphylla var. japonica), grown in a phytotron under natural daylight at two [CO(2)] levels (ambient: 400 µmol mol(-1) and elevated: 800 µmol mol(-1)) and limited N availability (90 mg N plant(-1)). Plants grown under elevated [CO(2)] exhibited photosynthetic downregulation, indicated by a decrease in the carboxylation capacity of Rubisco. At temperatures above 30°C, the net photosynthetic rates of elevated-CO(2)-grown plants exceeded those grown under ambient [CO(2)] when compared at their growth [CO(2)]. Electron transport rates were significantly lower in elevated-CO(2)-grown plants than ambient-CO(2)-grown ones at temperatures below 25°C. However, no significant difference was observed in the fraction of excess light energy [(1 - q(P))× F(v)'/F(m)'] between CO(2) treatments across the temperature range. The quantum yield of regulated non-photochemical energy loss was significantly higher in elevated-CO(2)-grown plants than ambient, when compared at their respective growth [CO(2)] below 25°C. These results suggest that elevated-CO(2)-induced downregulation might not exacerbate the temperature-dependent susceptibility to photoinhibition, because reduced energy consumption by electron transport was compensated for by increased thermal energy dissipation at low temperatures.
authors.affiliation: Department of Plant Ecology, Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba 305-8687, Japan.
authors.forename: Masabumi
authors.initials: M
authors.lastname: Komatsu
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tobita
authors.forename: Makoto
authors.initials: M
authors.lastname: Watanabe
authors.forename: Kenichi
authors.initials: K
authors.lastname: Yazaki
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Koike
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Kitao
mesh_terms: D029662:Betula / Q000201:enzymology / Q000502:physiology*; D002241:Carbohydrates / Q000032:analysis; D002245:Carbon Dioxide / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism; D015536:Down-Regulation; D009584:Nitrogen / Q000032:analysis; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000737:chemistry / Q000502:physiology; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013696:Temperature
chemical_list: D002241:Carbohydrates; D002734:Chlorophyll; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen