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Research article2023Peer reviewedOpen access

Components explain, but do eddy fluxes constrain? Carbon budget of a nitrogen-fertilized boreal Scots pine forest

Marshall, John D.; Tarvainen, Lasse; Zhao, Peng; Lim, Hyungwoo; Wallin, Goran; Nasholm, Torgny; Lundmark, Tomas; Linder, Sune; Peichl, Matthias

Abstract

  • Nitrogen (N) fertilization increases biomass and soil organic carbon (SOC) accumulation in boreal pine forests, but the underlying mechanisms remain uncertain. At two Scots pine sites, one undergoing annual N fertilization and the other a reference, we sought to explain these responses.
  • We measured component fluxes, including biomass production, SOC accumulation, and respiration, and summed them into carbon budgets. We compared the resulting summations to ecosystem fluxes measured by eddy covariance.
  • N fertilization increased most component fluxes (P < 0.05), especially SOC accumulation (20×). Only fine-root, mycorrhiza, and exudate production decreased, by 237 (SD = 28) g C m−2 yr−1. Stemwood production increases were ascribed to this partitioning shift, gross primary production (GPP), and carbon-use efficiency, in that order. The methods agreed in their estimates of GPP in both stands (P > 0.05), but the components detected an increase in net ecosystem production (NEP) (190 (54) g C m−2 yr−1; P < 0.01) that eddy covariance did not (19 (62) g C m−2 yr−1; ns).
  • The pairing of plots, the simplicity of the sites, and the strength of response provide a compelling description of N effects on the C budget. However, the disagreement between methods calls for further paired tests of N fertilization effects in simple forest ecosystems.

Keywords

canopy photosynthesis; carbon flux partitioning; carbon sequestration; carbon-use efficiency; eddy covariance; nitrogen fertilization

Published in

New Phytologist
2023, Volume: 239, number: 6, pages: 2166-2179 Publisher: WILEY