title: Modification of yield and chlorophyll content in leaf lettuce by HPS radiation and nitrogen treatments.
abstract: This study evaluated the potential of high photosynthetic photon flux (PPF) from high-pressure sodium (HPS) lamps, alone or in combination with metal halide (MH) plus quartz iodide (QI) incandescent lamps, to support lettuce growth, with or without N supplementation.  Varying exposures to radiation from combined HPS, MH, and QI lamps influenced dry weight gain and photosynthetic pigment content of hydroponically grown  Black-Seeded Simpson' lettuce (Lactuca sativa L.) seedlings.  Cumulative leaf dry weight declined with increasing exposure, up to 20 hours per day, to 660 micromoles m-2 s-1 of photosynthetically active radiation (PAR) from HPS lamps concomitant with constant 20 hours per day of 400 micromoles m-2 s-1 from MH + QI lamps.  Leaves progressively yellowed with increasing exposure to radiation from the three-lamp combination, corresponding to lower specific chlorophyll content but not to specific carotenoid content.  Lettuce grown under 20-hour photoperiods of 400, 473, or 668 micromoles m-2 s-1 from HPS radiation alone had the highest leaf dry weight at a PPF of 473 micromoles m-2 s-1.  Chlorophyll, but not carotenoid specific content, decreased with each incremental increase in PPF from HPS lamps.  Doubling the level of N in nutrient solution and supplying it as a combination of NH4+ and NO3- partially ameliorated adverse effects of high PPF on growth and pigment content relative to treatments using single-strength N as NO3-.
authors.affiliation: Center for Plant Environmental Stress Physiology, Department of Horticulture, Purdue University, West Lafayette, IN 47907.
authors.forename: C A
authors.initials: CA
authors.lastname: Mitchell
authors.forename: T
authors.initials: T
authors.lastname: Leakakos
authors.forename: T L
authors.initials: TL
authors.lastname: Ford
mesh_terms: D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D005069:Evaluation Studies as Topic; D008027:Light; D008029:Lighting; D009584:Nitrogen / Q000494:pharmacology*; D010788:Photosynthesis; D014675:Vegetables / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects
chemical_list: D002734:Chlorophyll; D002338:Carotenoids; D009584:Nitrogen