title: A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function.
abstract: Rapid environmental change at high latitudes is predicted to greatly alter the diversity, structure, and function of plant communities, resulting in changes in the pools and fluxes of nutrients. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying warming is known to impact plant diversity and ecosystem function; however, to date, most studies examining Arctic nutrient enrichment focus on the impact of relatively large (>25x estimated naturally occurring N enrichment) doses of nutrients on plant community composition and net primary productivity. To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming-induced fertilization. In addition, we compared our measured ecosystem CO2flux data to a widely used Arctic ecosystem exchange model to investigate the ability to predict the capacity for CO2exchange with nutrient addition. We observed declines in abundance-weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to the model, we found that the model explained roughly 30%-50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization-over an order of magnitude or more than warming-induced rates-significantly alter the capacity for tundra CO2exchange. Overall, our findings highlight the value of measuring and modeling the impacts of a nutrient enrichment gradient, as warming-related nutrient availability may impact ecosystems differently than single-level fertilization experiments.
authors.affiliation: Department of Ecology, Evolution, and Environmental Biology Columbia University New York NY USA.
authors.forename: Case M
authors.identifier: 0000-0001-9198-5586
authors.initials: CM
authors.lastname: Prager
authors.affiliation: Department of Ecology, Evolution, and Environmental Biology Columbia University New York NY USA.
authors.forename: Shahid
authors.initials: S
authors.lastname: Naeem
authors.affiliation: Department of Earth and Environmental Sciences Columbia University New York NY USA; Lamont-Doherty Earth Observatory Columbia University Palisades NY USA.
authors.forename: Natalie T
authors.initials: NT
authors.lastname: Boelman
authors.affiliation: Geospatial Laboratory for Environmental Dynamics Department of Natural Resources and Society University of Idaho Moscow ID USA; McCall Outdoor Science School University of Idaho McCall ID USA.
authors.forename: Jan U H
authors.initials: JU
authors.lastname: Eitel
authors.affiliation: Geospatial Laboratory for Environmental Dynamics Department of Natural Resources and Society University of Idaho Moscow ID USA.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Greaves
authors.affiliation: Ecosystems Center Marine Biological Laboratory Woods Hole MA USA.
authors.forename: Mary A
authors.initials: MA
authors.lastname: Heskel
authors.affiliation: Jet Propulsion Laboratory California Institute of Technology Pasadena CA USA.
authors.forename: Troy S
authors.initials: TS
authors.lastname: Magney
authors.affiliation: Department of Ecology, Evolution, and Environmental Biology Columbia University New York NY USA.
authors.forename: Duncan N L
authors.initials: DN
authors.lastname: Menge
authors.affiliation: Geospatial Laboratory for Environmental Dynamics Department of Natural Resources and Society University of Idaho Moscow ID USA; McCall Outdoor Science School University of Idaho McCall ID USA.
authors.forename: Lee A
authors.initials: LA
authors.lastname: Vierling
authors.affiliation: Department of Ecology, Evolution, and Environmental Biology Columbia University New York NY USA; Department of Earth and Environmental Sciences Columbia University New York NY USA; Lamont-Doherty Earth Observatory Columbia University Palisades NY USA.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Griffin
keywords: Arctic; climate change; ecosystem function; ecosystem respiration; gross primary productivity; net ecosystem CO2 exchange; plant diversity