Rising CO2 is starving boreal forests of nitrogen, study finds
A 57-year study of Swedish forests reveals that higher atmospheric carbon dioxide is reducing nitrogen availability in trees—a finding that could reshape how companies and governments assess forest productivity and carbon sequestration potential. The discovery challenges assumptions about how forests will respond to climate change and may require new strategies for forestry management.
Originaltitel: Rising atmospheric CO2 reduces nitrogen availability in boreal forests
Abstract Anthropogenic nitrogen (N) pollution is a cause of eutrophication globally 1 . However, recent datasets indicate that some ecosystems may be experiencing widespread oligotrophication—declining N availability—which is suggested to be a response to elevated atmospheric carbon dioxide (CO 2 ) 2 . Plant N isotope (δ 15 N) chronologies have served as primary evidence for oligotrophication, but there is wide disagreement whether rising CO 2 or temporal changes in N deposition explain these patterns 3–6 . Here we construct δ 15 N tree-ring chronologies using archived samples from Sweden’s 23.5-million-hectare forest area from 1961 to 2018. The study area spans a 1,500-km latitudinal distance where N deposition varies fourfold, but where rising CO 2 is spatially uniform. Our data show declining δ 15 N chronologies throughout Sweden, including forests in the far north where atmospheric N deposition rates are very low. Linear mixed-effects models showed that rising CO 2 is the strongest predictor of δ 15 N values, whereas N deposition variables, temperature and forest basal area had lower explanatory power. Our findings suggest that elevated atmospheric CO 2 is causing oligotrophication in boreal forests, which has implications for predicting their future role as sinks in the global carbon cycle 7–9 .