title: Nitrogen nutrition and temporal effects of enhanced carbon dioxide on soybean growth.
abstract: Plants grown on porous media at elevated CO2 levels generally have low concentrations of tissue N and often appear to require increased levels of external N to maximize growth response.  This study determines if soybean [Glycine max (L.) Merr.  Ransom'] grown hydroponically at elevated CO2 requires increases in external NO3- concentrations beyond levels that are optimal at ambient CO2 to maintain tissue N concentrations and maximize the growth response.  This study also investigates temporal influences of elevated CO2 on growth responses by soybean.  Plants were grown vegetatively for 34 d in hydroponic culture at atmospheric CO2 concentrations of 400, 650, and 900 microliters L-1 and during the final 18 d at NO3- concentrations of 0.5, 1.0, 5.0 and 10.0 mM in the culture solution.  At 650 and 900 microliters L-1 CO2, plants had maximum increases of 31 and 45% in dry weight during the experimental period.  Plant growth at 900 microliters L-1 CO2 was stimulated earlier than at 650 microliters L-1.  During the final 18 d of the experiment, the relative growth rates (RGR) of plants grown at elevated CO2 declined.  Elevated CO2 caused increases in total N and total NO3(-)-N content and leaf area but not leaf number.  Enhancing CO2 levels also caused a decrease in root:shoot ratios.  Stomatal resistance increased by 2.1- and 2.8-fold for plants at the 650 and 900 microliters L-1 CO2, respectively.  Nitrate level in the culture solutions had no effect on growth or on C:N ratios of tissues, nor did increases in CO2 levels cause a decrease in N concentration of plant tissues.  Hence, increases in NO3- concentration of the hydroponic solution were not necessary to maintain the N status of the plants or to maximize the growth response to elevated CO2.
authors.affiliation: Dep. of Plant Sci., Univ. of Manitoba, Winnipeg, Canada.
authors.forename: J K
authors.initials: JK
authors.lastname: Vessey
authors.forename: L T
authors.initials: LT
authors.lastname: Henry
authors.forename: C D
authors.initials: CD
authors.lastname: Raper
mesh_terms: D001692:Biological Transport; D002245:Carbon Dioxide / Q000494:pharmacology*; D005308:Fertilizers; D009566:Nitrates / Q000493:pharmacokinetics*; D009584:Nitrogen / Q000493:pharmacokinetics*; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development; D013025:Glycine max / Q000187:drug effects* / Q000254:growth & development*; D013997:Time Factors
chemical_list: D005308:Fertilizers; D009566:Nitrates; D002245:Carbon Dioxide; D009584:Nitrogen