Experimental evidence shows minor contribution of nitrogen deposition to global forest carbon sequestration

Lena F. Schulte-Uebbing*, Gerard H. Ros, Wim de Vries

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

14 Citations (Scopus)

Abstract

Human activities have drastically increased nitrogen (N) deposition onto forests globally. This may have alleviated N limitation and thus stimulated productivity and carbon (C) sequestration in aboveground woody biomass (AGWB), a stable C pool with long turnover times. This ‘carbon bonus’ of human N use partly offsets the climate impact of human-induced N2O emissions, but its magnitude and spatial variation are uncertain. Here we used a meta-regression approach to identify sources of heterogeneity in tree biomass C-N response (additional C stored per unit of N) based on data from fertilization experiments in global forests. We identified important drivers of spatial variation in forest biomass C-N response related to climate (potential evapotranspiration), soil fertility (N content) and tree characteristics (stand age), and used these relationships to quantify global spatial variation in N-induced forest biomass C sequestration. Results show that N deposition enhances biomass C sequestration in only one-third of global forests, mainly in the boreal region, while N reduces C sequestration in 5% of forests, mainly in the tropics. In the remaining 59% of global forests, N addition has no impact on biomass C sequestration. Average C-N responses were 11 (4–21) kg C per kg N for boreal forests, 4 (0–8) kg C per kg N for temperate forests and 0 (−4 to 5) kg C per kg N for tropical forests. Our global estimate of the N-induced forest biomass C sink of 41 (−53 to 159) Tg C yr−1 is substantially lower than previous estimates, mainly due to the absence of any response in most tropical forests (accounting for 58% of the global forest area). Overall, the N-induced C sink in AGWB only offsets ~5% of the climate impact of N2O emissions (in terms of 100-year global warming potential), and contributes ~1% to the gross forest C sink.

Original languageEnglish
Pages (from-to)899-917
JournalGlobal Change Biology
Volume28
Issue number3
Early online date26 Oct 2021
DOIs
Publication statusPublished - 2022

Keywords

  • aboveground woody biomass
  • C-N response
  • climate footprint
  • forest carbon sink
  • global warming potential
  • meta-regression
  • NO emissions
  • nitrogen deposition
  • spatial variation

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