title: Photosynthetic acclimation in relation to nitrogen allocation in cucumber leaves in response to changes in irradiance.
abstract: Leaves deep in canopies can suddenly be exposed to increased irradiances following e.g. gap formation in forests or pruning in crops. Studies on the acclimation of photosynthesis to increased irradiance have mainly focused on the changes in photosynthetic capacity (A(max)), although actual irradiance often remains below saturating level. We investigated the effect of changes in irradiance on the photosynthesis irradiance response and on nitrogen allocation in fully grown leaves of Cucumis sativus. Leaves that fully developed under low (50 µmol m⁻² s⁻¹) or moderate (200 µmol m⁻² s⁻¹) irradiance were subsequently exposed to, respectively, moderate (LM-leaves) or low (ML-leaves) irradiance or kept at constant irradiance level (LL- and MM-leaves). Acclimation of photosynthesis occurred within 7 days with final A(max) highest in MM-leaves, lowest in LL-leaves and intermediate in ML- and LM-leaves, whereas full acclimation of thylakoid processes underlying photosystem II (PSII) efficiency and non-photochemical quenching occurred in ML- and LM-leaves. Dark respiration correlated with irradiance level, but not with A(max). Light-limited quantum efficiency was similar in all leaves. The increase in photosynthesis at moderate irradiance in LM-leaves was primarily driven by nitrogen import, and nitrogen remained allocated in a similar ratio to Rubisco and bioenergetics, while allocation to light harvesting relatively decreased. A contrary response of nitrogen was associated with the decrease in photosynthesis in ML-leaves. Net assimilation of LM-leaves under moderate irradiance remained lower than in MM-leaves, revealing the importance of photosynthetic acclimation during the leaf developmental phase for crop productivity in scenarios with realistic, moderate fluctuations in irradiance that leaves can be exposed to.
authors.affiliation: Department of Plant Sciences, Horticultural Supply Chains Group, Wageningen University, Wageningen, The Netherlands.
authors.forename: Govert
authors.initials: G
authors.lastname: Trouwborst
authors.forename: Sander W
authors.initials: SW
authors.lastname: Hogewoning
authors.forename: Jeremy
authors.initials: J
authors.lastname: Harbinson
authors.forename: Wim
authors.initials: W
authors.lastname: van Ieperen
mesh_terms: D000064:Acclimatization; D001692:Biological Transport; D018553:Cucumis sativus / Q000502:physiology* / Q000528:radiation effects*; D007700:Kinetics; D008027:Light; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000528:radiation effects; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D020524:Thylakoids / Q000528:radiation effects; D013997:Time Factors
chemical_list: D045332:Photosystem II Protein Complex; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen