Michael Gundale receives large Wallenberg grant for research on declining nitrogen supply in forests
Michael Gundale has been awarded SEK 26 million by the Knut and Alice Wallenberg Foundation to investigate whether nitrogen deficiency is impairing forests' ability to store carbon. He recently showed that nitrogen availability in boreal forests decreases as atmospheric carbon dioxide levels rise.
Knut and Alice Wallenberg Foundation is awarding SEK 900 million to 30 research projects that have been judged innovative and at the forefront of international research.
One of the funded projects is titled “Progressive nitrogen limitation as a driver of the boreal forest carbon sink” and has been awarded SEK 26 million over five years. The principal investigator is Michael Gundale, Professor of Forest Vegetation Ecology at the Swedish University of Agricultural Sciences (SLU) in Umeå. Co-applicants are Professor Björn Lindahl from SLU in Uppsala and Senior Lecturer Thomas Pugh from Lund University.
Can we rely on forests in climate change mitigation?
Boreal forests—blanketing the Northern Hemisphere with spruce and pine—have long helped mitigate global warming by absorbing and storing the carbon dioxide emitted by humans. We have grown accustomed to relying on these forests to continue acting as carbon sinks, but new research indicates that we can no longer take this for granted.
The major issue is nitrogen availability. Trees require nitrogen for growth, and the supply of nitrogen influences the amount of carbon dioxide forests can absorb. For decades, researchers assumed that nitrogen deposition and rising temperatures would increase nitrogen availability in our forests—thereby boosting carbon sequestration—but we are now seeing that nitrogen appears to be in short supply. A groundbreaking study by Michael Gundale’s research group reveals that the availability of the specific type of nitrogen trees use as a nutrient is steadily declining as atmospheric carbon dioxide levels rise.
Although it is unclear whether declining nitrogen availability is currently affecting tree growth, the long-term consequence could be a weakened carbon sink that fails to keep pace with rising atmospheric carbon dioxide levels. Investigating whether nitrogen deficiency is impairing the forests' capacity to store carbon is therefore a matter of great importance.
The answer may lie in the soil
Michael Gundale suggests that the answer to the question may lie in the soil, where a multitude of fungi and bacteria work feverishly to break down old trees and plants, converting them into new nutrients within the cycle of life. Beneath the soil surface, trees rely on symbiotic interactions with fungi—specifically, ectomycorrhizae. Among these are fungal species that efficiently break down organic matter to release nitrogen; however, this process also releases stored carbon. To sustain growth as nitrogen levels decline, trees turn to these fungi, fostering them at the expense of soil carbon. This presents a problem, given that boreal soils store five times as much carbon as the trees themselves. Alternatively, tree growth can also be sustained by nitrogen-fixing bacteria that introduce biologically active nitrogen from the atmosphere into the forest ecosystem, yet our understanding of how this process is affected by declining nitrogen levels remains very limited.
Collaboration with leading researchers
In the NitroLimit project, Gundale, Lindahl, and Pugh will collaborate to investigate how nitrogen availability affects boreal forests in Sweden, as well as in other parts of Scandinavia, Alaska, Canada, and China. Using nitrogen isotope analysis—a method that detects chemical signatures in wood—the team will map nitrogen availability across different forest types. They will combine this data with DNA sequencing and computer models to understand how reduced nitrogen availability impacts soil-dwelling bacteria and fungi.
“By clarifying the link between carbon and nitrogen in our forests and integrating this into today’s leading climate models, the project will provide a clearer picture of the forests' future capacity to sequester carbon. This will, in turn, enable us to make more accurate climate projections,” says Michael Gundale.
Link to press release from the Knut and Alice Wallenberg Foundation
The article in Nature
Bassett, K.R., Hupperts, S.F., Jämtgård, S. et al. Rising atmospheric CO2 reduces nitrogen availability in boreal forests. Nature 650, 629–635 (2026). https://www.nature.com/articles/s41586-025-10039-5
Contact details
Michael Gundale, Professor
Department of Forest Ecology and Management
Swedish University of Agricultural Sciences, Umeå
michael.gundale@slu.se, +46706186946, +46907868427