title: Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies.
abstract: Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (< 1 week after 15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3-18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C:N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N x ha(-1) x yr(-1) above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.
authors.affiliation: Department of Biology, Boston University, 5 Cummington Street, Boston, Massachusetts 02215, USA. ptempler@bu.edu
authors.forename: P H
authors.initials: PH
authors.lastname: Templer
authors.forename: M C
authors.initials: MC
authors.lastname: Mack
authors.forename: F S
authors.initials: FS
authors.lastname: Chapin
authors.forename: L M
authors.initials: LM
authors.lastname: Christenson
authors.forename: J E
authors.initials: JE
authors.lastname: Compton
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authors.initials: HD
authors.lastname: Crook
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authors.lastname: Currie
authors.forename: C J
authors.initials: CJ
authors.lastname: Curtis
authors.forename: D B
authors.initials: DB
authors.lastname: Dail
authors.forename: C M
authors.initials: CM
authors.lastname: D'Antonio
authors.forename: B A
authors.initials: BA
authors.lastname: Emmett
authors.forename: H E
authors.initials: HE
authors.lastname: Epstein
authors.forename: C L
authors.initials: CL
authors.lastname: Goodale
authors.forename: P
authors.initials: P
authors.lastname: Gundersen
authors.forename: S E
authors.initials: SE
authors.lastname: Hobbie
authors.forename: K
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authors.lastname: Holland
authors.forename: D U
authors.initials: DU
authors.lastname: Hooper
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authors.initials: BA
authors.lastname: Hungate
authors.forename: S
authors.initials: S
authors.lastname: Lamontagne
authors.forename: K J
authors.initials: KJ
authors.lastname: Nadelhoffer
authors.forename: C W
authors.initials: CW
authors.lastname: Osenberg
authors.forename: S S
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authors.lastname: Perakis
authors.forename: P
authors.initials: P
authors.lastname: Schleppi
authors.forename: J
authors.initials: J
authors.lastname: Schimel
authors.forename: I K
authors.initials: IK
authors.lastname: Schmidt
authors.forename: M
authors.initials: M
authors.lastname: Sommerkorn
authors.forename: J
authors.initials: J
authors.lastname: Spoelstra
authors.forename: A
authors.initials: A
authors.lastname: Tietema
authors.forename: W W
authors.initials: WW
authors.lastname: Wessel
authors.forename: D R
authors.initials: DR
authors.lastname: Zak
mesh_terms: D000531:Altitude; D000641:Ammonia / Q000737:chemistry; D055884:Chemical Hazard Release; D017753:Ecosystem; D009566:Nitrates / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry*; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes; D011891:Rain; D013696:Temperature
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D000641:Ammonia; D009584:Nitrogen