title: Seasonal changes in photosynthesis, nitrogen content and nitrogen partitioning in Lindera umbellata leaves grown in high or low irradiance.
abstract: Seasonal changes in photosynthetic capacity, leaf nitrogen (N) content and N partitioning were studied from before leaf maturation (spring) until death (autumn) in high- and low-light-exposed leaves of a deciduous shrub, Lindera umbellata var. membranacea (Maxim.) Momiyama growing in a natural forest in northeast Japan. In spring, light-saturated photosynthetic rate (Pmax) was low despite high leaf N and Rubisco contents, indicating that the photosynthetic apparatus was not yet functionally developed. Rubisco seemed to be only partially active. In summer and autumn, Pmax per unit leaf N increased and changes in Pmax were correlated with changes in leaf N and two photosynthetic components, Rubisco and chlorophyll. Changes in these components paralleled the changes in leaf N. During leaf senescence, about 70% of leaf N was resorbed. Metabolic proteins that accounted for the majority of leaf N in summer were highly degradable and more than sufficient to explain the high N-resorption efficiency. Structural proteins represented only a small part of leaf N and were relatively resistant to degradation and thus contributed little to N resorption. Leaf N partitioning between metabolic and structural proteins determined the amount of retranslocatable N, but did not strictly determine the N content of a dead leaf or N-resorption efficiency.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Sendai 980-8578, Japan. yukes@affrc.go.jp
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yasumura
authors.forename: Kouki
authors.initials: K
authors.lastname: Hikosaka
authors.forename: Tadaki
authors.initials: T
authors.lastname: Hirose
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D027443:Lindera / Q000502:physiology*; D017672:Nitrogen Compounds / Q000378:metabolism*; D010788:Photosynthesis / Q000528:radiation effects; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D010940:Plant Proteins / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D012621:Seasons; D013472:Sunlight; D014197:Trees / Q000502:physiology*
chemical_list: D017672:Nitrogen Compounds; D010940:Plant Proteins; D002734:Chlorophyll; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase