title: Increasing plant use of organic nitrogen with elevation is reflected in nitrogen uptake rates and ecosystem delta15N.
abstract: It is hypothesized that decreasing mean annual temperature and rates of nitrogen (N) cycling causes plants to switch from inorganic to organic forms of N as the primary mode of N nutrition. To test this hypothesis, we conducted field experiments and collected natural-abundance delta15N signatures of foliage, soils, and ectomycorrhizal sporocarps along a steep elevation-climate gradient in the White Mountains, New Hampshire, USA. Here we show that with increasing elevation organic forms of N became the dominant source of N taken up by hardwood and coniferous tree species based on dual-labeled glycine uptake analysis, an important confirmation of an emerging theory for the biogeochemistry of the N cycle. Variation in natural abundance foliar delta15N with elevation was also consistent with increasing organic N uptake, though a simple, mass balance model demonstrated that the uptake of delta15N depleted inorganic N, rather than fractionation upon transfer of N from mycorrhizal fungi, best explains variations in foliar delta15N with elevation.
authors.affiliation: Department of Biology, Boston University, 5 Cummington Street, Boston, Massachusetts 02215, USA. colin.averill@gmail.com
authors.forename: Colin
authors.initials: C
authors.lastname: Averill
authors.forename: Adrien
authors.initials: A
authors.lastname: Finzi
mesh_terms: D000531:Altitude; D017753:Ecosystem; D038821:Mycorrhizae; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000737:chemistry / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry; D010944:Plants / Q000378:metabolism*; D012987:Soil / Q000737:chemistry
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D009584:Nitrogen