Abstract

The boreal forest is an important global carbon (C) sink. Since low soil nitrogen (N) availability is commonly a key constraint on forest productivity, the prevalent view is that increased N input enhances its C sink-strength. This understanding however relies primarily on observations of increased aboveground tree biomass and soil C stock following N fertilization, whereas empirical data evaluating the effects on the whole ecosystem-scale C balance are lacking. Here we use a unique long-term experiment consisting of paired forest stands with eddy covariance measurements to explore the effect of ecosystem-scale N fertilization on the C balance of a managed boreal pine forest. We find that the annual C uptake (i.e. net ecosystem production, NEP) at the fertilized stand was 16 +/- 2% greater relative to the control stand by the end of the first decade of N addition. Subsequently, the ratio of NEP between the fertilized and control stand remained at a stable level during the following five years with an average NEP to N response of 7 & PLUSMN; 1 g C per g N. Our study reveals that this non-linear response of NEP to long-term N fertilization was the result of a cross-seasonal feedback between the N-induced increases in both growing-season C uptake and subsequent winter C emission. We further find that one decade of N addition altered the sensitivity of ecosystem C fluxes to key environmental drivers resulting in divergent responses to weather patterns. Thus, our study highlights the need to account for ecosystem-scale responses to perturbations to improve our understanding of nitrogen-carbon-climate feedbacks in boreal forests.

Keywords

Boreal forest; Carbon sequestration; Climate change; Eddy covariance; Forest management; Nitrogen fertilization

Published in

Agricultural and Forest Meteorology
2022, Volume: 324, article number: 109112
Publisher: ELSEVIER

SLU Authors

• Zhao, Peng

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Chi, Jinshu

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • The Hong Kong University of Science and Technology (HKUST)

• Nilsson, Mats

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Ottosson Löfvenius, Mikaell

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Högberg, Peter

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Lim, Hyungwoo

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • University of Tartu

• Marshall, John

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Ratcliffe, Joshua

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Näsholm, Torgny

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Lundmark, Tomas

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Linder, Sune

  • Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
    

• Peichl, Matthias

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

Associated SLU-program

SLU Forest Damage Center


UKÄ Subject classification

Climate Research
Forest Science


Publication identifier

DOI: https://doi.org/10.1016/j.agrformet.2022.109112

Permanent link to this page (URI)

https://res.slu.se/id/publ/119258