Nitrogen-fixing trees could exacerbate climate change under elevated nitrogen deposition

Sian Kou-Giesbrecht,Duncan Menge

doi:10.1038/s41467-019-09424-2

Sian Kou-Giesbrecht, Duncan Menge

Open Access

https://doi.org/10.1038/s41467-019-09424-2

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Journal: Nature Communications	Publication Date: Apr 2, 2019
Citations: 43	License type: open-access

Affiliation: Columbia University

Abstract

Biological nitrogen fixation can fuel CO2 sequestration by forests but can also stimulate soil emissions of nitrous oxide (N2O), a potent greenhouse gas. Here we use a theoretical model to suggest that symbiotic nitrogen-fixing trees could either mitigate (CO2 sequestration outweighs soil N2O emissions) or exacerbate (vice versa) climate change relative to non-fixing trees, depending on their nitrogen fixation strategy (the degree to which they regulate nitrogen fixation to balance nitrogen supply and demand) and on nitrogen deposition. The model posits that nitrogen-fixing trees could exacerbate climate change globally relative to non-fixing trees by the radiative equivalent of 0.77 Pg C yr−1 under nitrogen deposition rates projected for 2030. This value is highly uncertain, but its magnitude suggests that this subject requires further study and that improving the representation of biological nitrogen fixation in climate models could substantially decrease estimates of the extent to which forests will mitigate climate change.

Highlights

Biological nitrogen fixation can fuel CO2 sequestration by forests but can stimulate soil emissions of nitrous oxide (N2O), a potent greenhouse gas
Our model suggests that N-fixing trees can either mitigate climate change relative to non-fixing trees or exacerbate climate change relative to non-fixing trees
The main controls that determine this balance are N fixation strategy and N deposition rate (Fig. 1 displays results for tropical forests and Supplementary Figures 1 and 2 display results for temperate and boreal forests respectively; because patterns are analogous between tropical, temperate, and boreal forests we hereafter focus on tropical forests)

Summary

Introduction

Biological nitrogen fixation can fuel CO2 sequestration by forests but can stimulate soil emissions of nitrous oxide (N2O), a potent greenhouse gas. We use a theoretical model to suggest that symbiotic nitrogen-fixing trees could either mitigate (CO2 sequestration outweighs soil N2O emissions) or exacerbate (vice versa) climate change relative to nonfixing trees, depending on their nitrogen fixation strategy (the degree to which they regulate nitrogen fixation to balance nitrogen supply and demand) and on nitrogen deposition. The model posits that nitrogen-fixing trees could exacerbate climate change globally relative to non-fixing trees by the radiative equivalent of 0.77 Pg C yr−1 under nitrogen deposition rates projected for 2030. We use a theoretical modeling approach to ask two main questions: how do N-fixing trees influence the net CO2–N2O effect of forests, i.e. do N-fixing trees mitigate or exacerbate climate change?

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Conclusion