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)