title: Contrasting effects of elevated CO2 and warming on nitrogen cycling in a semiarid grassland.
abstract: *Simulation models indicate that the nitrogen (N) cycle plays a key role in how other ecosystem processes such as plant productivity and carbon (C) sequestration respond to elevated CO(2) and warming. However, combined effects of elevated CO(2) and warming on N cycling have rarely been tested in the field. *Here, we studied N cycling under ambient and elevated CO(2) concentrations (600 micromol mol(-1)), and ambient and elevated temperature (1.5 : 3.0 degrees C warmer day:night) in a full factorial semiarid grassland field experiment in Wyoming, USA. We measured soil inorganic N, plant and microbial N pool sizes and NO(3)(-) uptake (using a (15)N tracer). *Soil inorganic N significantly decreased under elevated CO(2), probably because of increased microbial N immobilization, while soil inorganic N and plant N pool sizes significantly increased with warming, probably because of increased N supply. We observed no CO(2 )x warming interaction effects on soil inorganic N, N pool sizes or NO(3)(-) uptake in plants and microbes. *Our results indicate a more closed N cycle under elevated CO(2) and a more open N cycle with warming, which could affect long-term N retention, plant productivity, and C sequestration in this semiarid grassland.
authors.affiliation: Rangeland Resources Research Unit, USDA-ARS, Crops Research Laboratory, 1701 Centre Ave, Fort Collins, CO 80526, USA.
authors.forename: Feike A
authors.initials: FA
authors.lastname: Dijkstra
authors.affiliation: Rangeland Resources Research Unit, USDA-ARS, Crops Research Laboratory, 1701 Centre Ave, Fort Collins, CO 80526, USA.
authors.forename: Dana
authors.initials: D
authors.lastname: Blumenthal
authors.affiliation: Rangeland Resources Research Unit, USDA-ARS, Crops Research Laboratory, 1701 Centre Ave, Fort Collins, CO 80526, USA.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Morgan
authors.affiliation: Department of Botany and Program in Ecology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Elise
authors.initials: E
authors.lastname: Pendall
authors.affiliation: Department of Botany and Program in Ecology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Yolima
authors.initials: Y
authors.lastname: Carrillo
authors.affiliation: Soil, Plant, and Nutrient Research Unit, USDA-ARS, 2150 Centre Ave, Fort Collins, CO 80526, USA.
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Follett
mesh_terms: D001419:Bacteria / Q000187:drug effects / Q000254:growth & development; D018533:Biomass; D002245:Carbon Dioxide / Q000494:pharmacology*; D003889:Desert Climate; D057232:Global Warming; D007553:Isotope Labeling; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D006109:Poaceae / Q000187:drug effects* / Q000378:metabolism*; D012987:Soil / Q000032:analysis; D013696:Temperature; D014867:Water / Q000378:metabolism
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D014867:Water; D002245:Carbon Dioxide; D009584:Nitrogen