title: Root-zone temperature and nitrogen affect the yield and secondary metabolite concentration of fall- and spring-grown, high-density leaf lettuce.
abstract: BACKGROUND
  Understanding the effects of temperature and nitrogen levels on key variables, particularly under field conditions during cool seasons of temperate climates, is important. Here, we document the impact of root-zone heating and nitrogen (N) fertility on the accumulation and composition of fall- and spring-grown lettuce biomass. A novel, scalable field system was employed.
  
  
  RESULTS
  Direct-seeded plots containing a uniform, semi-solid, and nearly stable rooting medium were established outdoors in 2009 and 2010; each contained one of eight combinations of root-zone heating (-/+) and N fertility (0, 72, 144, and 576 mg day(-1)). Root-zone heating increased but withholding N decreased biomass accumulation in both years. Low N supplies were also associated with greater anthocyanin and total antioxidant power but lower N and phosphorus levels. Tissue chlorophyll a and vitamin C levels tracked root-zone temperature and N fertility more closely in 2009 and 2010, respectively.
  
  
  CONCLUSIONS
  Experimentally imposed root-zone temperature and N levels influenced the amount and properties of fall- and spring-grown lettuce tissue. Ambient conditions, however, dictated which of these factors exerted the greatest effect on the variables measured. Collectively, the results point to the potential for gains in system sustainability and productivity, including with respect to supplying human nutritional units.
authors.affiliation: The Ohio State University-OARDC, Horticulture and Crop Science, Wooster, OH 44691 USA.
authors.forename: Natalie R
authors.initials: NR
authors.lastname: Bumgarner
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Scheerens
authors.forename: Robert W
authors.initials: RW
authors.lastname: Mullen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Bennett
authors.forename: Peter P
authors.initials: PP
authors.lastname: Ling
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Kleinhenz
mesh_terms: D000872:Anthocyanins / Q000378:metabolism; D000975:Antioxidants / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism; D018533:Biomass; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D005308:Fertilizers; D006801:Humans; D018545:Lactuca / Q000254:growth & development / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots; D012621:Seasons; D012987:Soil; D013696:Temperature
chemical_list: D000872:Anthocyanins; D000975:Antioxidants; D005308:Fertilizers; D012987:Soil; D002734:Chlorophyll; D010758:Phosphorus; D009584:Nitrogen; D001205:Ascorbic Acid; D000077194:Chlorophyll A