title: Plant delta 15N correlates with the transpiration efficiency of nitrogen acquisition in tropical trees.
abstract: Based upon considerations of a theoretical model of (15)N/(14)N fractionation during steady-state nitrate uptake from soil, we hypothesized that, for plants grown in a common soil environment, whole-plant delta(15)N (deltaP) should vary as a function of the transpiration efficiency of nitrogen acquisition (F(N)/v) and the difference between deltaP and root delta(15)N (deltaP - deltaR). We tested these hypotheses with measurements of several tropical tree and liana species. Consistent with theoretical expectations, both F(N)/v and deltaP - deltaR were significant sources of variation in deltaP, and the relationship between deltaP and F(N)/v differed between non-N(2)-fixing and N(2)-fixing species. We interpret the correlation between deltaP and F(N)/v as resulting from variation in mineral nitrogen efflux-to-influx ratios across plasma membranes of root cells. These results provide a simple explanation of variation in delta(15)N of terrestrial plants and have implications for understanding nitrogen cycling in ecosystems.
authors.affiliation: Smithsonian Tropical Research Institute, Balboa, Ancon, Republic of Panama. lucas.cernusak@cdu.edu.au
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Cernusak
authors.forename: Klaus
authors.initials: K
authors.lastname: Winter
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Turner
mesh_terms: D008954:Models, Biological; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018526:Plant Transpiration; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012044:Regression Analysis; D012987:Soil / Q000032:analysis*; D014197:Trees / Q000378:metabolism*; D014329:Tropical Climate
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D012987:Soil; D009584:Nitrogen