Forest uptake of carbon dioxide (CO₂) sequesters carbon which mitigates climate change. However, some of this benefit is offset when another greenhouse gas, nitrous oxide (N₂O), is released from soils. The net balance of CO₂ and N₂O gases differs among forests, particularly for nitrogen-fixing trees used widely in reforestation. Researchers used field and modeling studies to compare how nitrogen-fixing and non-fixing trees affect climate mitigation by these two gases. They found that nitrogen-fixing trees best mitigate climate change on infertile soils, because they obtain their own nitrogen to support growth and CO₂ uptake. However, on fertile soils or where background nitrogen levels are high, nitrogen-fixing trees stimulate N₂O release and become less effective at climate mitigation.  These results can guide forest management aimed at climate mitigation by clarifying the benefits of nitrogen-fixing trees and highlighting their risks when grown in regions where nitrogen is abundant in the environment.

Kou-Giesbrecht, S., Funk, J.L., Perakis, S.S., Wolf, A.A., Menge, D.N., 2021, N supply mediates the radiative balance of N₂O emissions and CO₂ sequestration driven by N-fixing vs. non-fixing trees: Ecology, no. e03414, https://doi.org/10.1002/ecy.3414.

(Photo credits, Robinia pseudoacacia: Larry Allain, U.S. Geological Survey)