title: Influence of N doses and form on ¹⁵N natural abundance of pepper plants: considerations for using δ¹⁵N values as indicator of N source.
abstract: BACKGROUND
  The aim of this study was to ascertain the effect of the N form (NO(3) (-) , NH(4) (+) and organic N) and N concentration on plant isotopic fractionation and on the contribution of the different N sources to the plant N budget, in order to evaluate the feasibility of using plant δ(15) N values for discriminating between conventional and organic crops. To this end, different N concentrations (applied as NO(3) (-) ), N forms (NO(3) (-) versus NH(4) (+) ), and increasing NO(3) (-) applications to an organic N-based fertilization regime were studied.
  
  
  RESULTS
  When using NO(3) (-) as N source, intra-plant fractionation was significant and tended to increase when NO(3) (-) concentration increased in the root medium. However, negligible net isotopic fractionation was observed when comparing theoretical and measured plant δ(15) N values. On the other hand, when plants are fertilized with a mixture of NO(3) (-) and NH(4) (+) , differences in uptake patterns for both salts could result in variation in plant δ(15) N regarding to the expected value. Finally, the application of NO(3) (-) to plants was detected when it was combined with high levels of organic N sources, from 99:1 organic:inorganic N ratio.
  
  
  CONCLUSIONS
  Under certain conditions and following some considerations concerning sampling, δ(15) N values can be considered to be a potential tool to guarantee the authenticity of organic products.
authors.affiliation: Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario, La Alberca, Murcia 30150, Spain. mpilar.flores@carm.es
authors.forename: Pilar
authors.initials: P
authors.lastname: Flores
authors.forename: Phil J
authors.initials: PJ
authors.lastname: Murray
authors.forename: Pilar
authors.initials: P
authors.lastname: Hellín
authors.forename: Jose
authors.initials: J
authors.lastname: Fenoll
mesh_terms: D000465:Algorithms; D002212:Capsicum / Q000254:growth & development* / Q000378:metabolism*; D005240:Feasibility Studies; D005308:Fertilizers; D005513:Food Inspection / Q000379:methods*; D058870:Food, Organic / Q000032:analysis*; D005638:Fruit / Q000378:metabolism*; D008372:Manure; D009566:Nitrates / Q000378:metabolism; D009574:Nitro Compounds / Q000378:metabolism; D017672:Nitrogen Compounds / Q000378:metabolism; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
chemical_list: D005308:Fertilizers; D008372:Manure; D009566:Nitrates; D009574:Nitro Compounds; D017672:Nitrogen Compounds; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds