title: Morning reduction of photosynthetic capacity before midday depression.
abstract: Midday depression of photosynthesis has important consequences for ecosystem carbon exchange. Recent studies of forest trees have demonstrated that latent reduction of photosynthetic capacity can begin in the early morning, preceding the midday depression. We investigated whether such early morning reduction also occurs in an herbaceous species, Oenothera biennis. Diurnal changes of the photosynthetic light response curve (measured using a light-emitting diode) and incident sunlight intensity were measured under field conditions. The following results were obtained: (1) the light-saturated photosynthetic rate decreased beginning at sunrise; (2) the incident sunlight intensity on the leaves increased from sunrise; and (3) combining (1) and (2), the net photosynthetic rate under natural sunlight intensity increased from sunrise, reached a maximum at mid-morning, and then showed midday depression. Our results demonstrate that the latent morning reduction of photosynthetic capacity begins at sunrise, preceding the apparent midday depression, in agreement with previous studies of forest trees.
authors.affiliation: 1] Department of Life Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan [2] Department of Environmental Science, Ishikawa Prefectural University, Nonoichi, Ishikawa 921-8836, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Koyama
authors.affiliation: The University of Tokyo Tanashi Forest, Graduate School of Agricultural & Life Sciences, 1-1-8 Midoricho, Nishitokyo, Tokyo 188-0002, Japan.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Takemoto
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D017753:Ecosystem; D031665:Oenothera biennis / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D018515:Plant Leaves / Q000502:physiology* / Q000528:radiation effects; D012621:Seasons; D013472:Sunlight
chemical_list: D002245:Carbon Dioxide