title: Respiration rate in maize roots is related to concentration of reduced nitrogen and proliferation of lateral roots.
abstract: The relationship between specific rate of respiration (respiration rate per unit root dry weight) and concentration of reduced nitrogen was examined for maize (Zea mays L.) roots.  Plants with 2 primary nodal root axes were grown for 8 days in a split-root hydroponic system in which NO3- was supplied to both axes at 1.0 mol m-3, to one axis at 1.0 mol m-3 and the other axis at 0.0 mol m-3, or to both axes at 0.0 mol m-3.  Respiration rates and root characteristics were measured at 2-day intervals.  Specific rate of respiration was positively correlated in a nonlinear relationship with concentration of reduced nitrogen.  The lowest specific rates of respiration occurred when neither axis received exogenous NO3- and the concentration of reduced nitrogen in the axes was less than 9 mg g-1.  The greatest rates occurred in axes that were actively absorbing NO3- and contained more than 35 mg g-1 of reduced nitrogen.  At 23 mg g-1 of reduced nitrogen, below which initiation of lateral branches was decreased by 30-50%, specific rate of respiration was 17% greater for roots actively absorbing NO3- than for roots not absorbing NO3-.  Increases in specific rate of respiration associated with concentrations of reduced nitrogen greater than 23 mg g-1 were concluded to be attributable primarily to proliferation of lateral branches.
authors.affiliation: Dept of Soil Science, North Carolina State Univ., Raleigh 27695-7619, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Granato
authors.forename: C D
authors.initials: CD
authors.lastname: Raper
authors.forename: G G
authors.initials: GG
authors.lastname: Wilkerson
mesh_terms: D002245:Carbon Dioxide; D019069:Cell Respiration; D003470:Culture Media; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism*; D003313:Zea mays / Q000254:growth & development / Q000378:metabolism*
chemical_list: D003470:Culture Media; D009566:Nitrates; D002245:Carbon Dioxide; D009584:Nitrogen