title: Genotypic variation in nitrogen isotope discrimination in Populus balsamifera L. clones grown with either nitrate or ammonium.
abstract: Intraspecific variability in nitrogen use has not been comprehensively assessed in a natural poplar species. Here, a nitrogen isotope mass balance approach was used to assess variability in nitrogen uptake, assimilation and allocation traits in 25 genotypes from five climatically dispersed provenances of Populus balsamifera L. grown hydroponically with either nitrate or ammonium. Balsam poplar was able to grow well with either ammonium or nitrate as the sole nitrogen source. Variation within provenances exceeded significant provenance level variation. Interestingly, genotypes with rapid growth on nitrate achieved similar growth with ammonium. In most cases, the root:shoot ratio was greater in plants grown with ammonium. However, there were genotypes where root:shoot ratio was lower for some genotypes grown with ammonium compared to nitrate. Tissue nitrogen concentration was greater in the leaves and stems but not the roots for plants grown with ammonium compared to nitrate. There was extensive genotypic variation in organ-level nitrogen isotope composition. Root nitrogen isotope discrimination was greater under nitrate than ammonium, but leaf nitrogen isotope discrimination was not significantly different between plants on different sources. This can indicate variation in partitioning of nitrogen assimilation, efflux/influx (E/I) and root or leaf assimilation rates. The proportion of nitrogen assimilated in roots was lower under nitrate than ammonium. E/I was lower for nitrate than ammonium. With the exception of E/I, genotype-level variations in nitrogen-use traits for nitrate were correlated with the same traits when grown with ammonium. Using the nitrogen isotope mass balance model, a high degree of genotypic variation in nitrogen use traits was identified at both the provenance and, more extensively, the genotypic level.
authors.affiliation: Department of Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada; Department of Horticulture, College of Agriculture and Natural Resource Sciences, Washington State University, Pullman, WA, United States; Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA, United States.
authors.forename: Lee A
authors.initials: LA
authors.lastname: Kalcsits
authors.affiliation: Department of Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada. Electronic address: rob.guy@ubc.ca.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Guy
mesh_terms: D064751:Ammonium Compounds / Q000494:pharmacology*; D018533:Biomass; D002999:Clone Cells; D014644:Genetic Variation; D005838:Genotype; D009566:Nitrates / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism; D009587:Nitrogen Isotopes; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D018547:Plant Stems / Q000187:drug effects / Q000378:metabolism; D032107:Populus / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D009587:Nitrogen Isotopes; D009584:Nitrogen
keywords: Intraspecific variation; Nitrogen assimilation; Nitrogen fluxes; Nitrogen partitioning