Elevated CO2 promotes long‐term nitrogen accumulation only in combination with nitrogen addition. (18th November 2015)

• Record Type: Journal Article
• Authors: Pastore, Melissa A.; Megonigal, J. Patrick; Langley, J. Adam
• Is Part Of: Global change biology. Volume 22:Number 1(2016:Jan.)
• Page Start: 391
• Page End: 403
• Publication Date: 2015-11-18
• Subjects: brackish marsh -- CO2 enrichment -- denitrification -- isotopic biogeochemistry -- nitrogen pollution -- nitrogen retention and loss; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.13112
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Biogeochemical models that incorporate nitrogen (N) limitation indicate that N availability will control the magnitude of ecosystem carbon uptake in response to rising CO2 . Some models, however, suggest that elevated CO2 may promote ecosystem N accumulation, a feedback that in the long term could circumvent N limitation of the CO2 response while mitigating N pollution. We tested this prediction using a nine‐year CO2 xN experiment in a tidal marsh. Although the effects of CO2 are similar between uplands and wetlands in many respects, this experiment offers a greater likelihood of detecting CO2 effects on N retention on a decadal timescale because tidal marshes have a relatively open N cycle and can accrue soil organic matter rapidly. To determine how elevated CO2 affects N dynamics, we assessed the three primary fates of N in a tidal marsh: (1) retention in plants and soil, (2) denitrification to the atmosphere, and (3) tidal export. We assessed changes in N pools and tracked the fate of a 15 N tracer added to each plot in 2006 to quantify the fraction of added N retained in vegetation and soil, and to estimate lateral N movement. Elevated CO2 alone did not increase plant N mass, soil N mass, or 15 N label retention. Unexpectedly, CO2 and N interacted such that the combined N+CO2 treatment increased ecosystem N accumulation despite the stimulation in N losses indicated by reduced 15 N label retention. These findings suggest that in N‐limited ecosystems, elevated CO2 is unlikely to increase long‐term N accumulation and circumvent progressive N limitation without additional N inputs, which may relieve plant–microbe competition and allow for increased plant N uptake.