In order to use nitrogen, the element must be fixed in the soil with the help of microorganisms. This biological binding occurs in natural ecosystems, but also on agricultural land. “While this process has been significantly overestimated in nature, it has increased by 75 percent over the past 20 years due to agriculture,” Bettina Weber, biologist at the University of Graz, summarises the findings of a publication from earlier this year.
A new study based on these results now shows that existing calculations on nitrogen fixation in certain Earth System models, which are used, among other things, in the World Climate Report, have been revised. This is the conclusion of the new study, which has been published on 24 November in the scientific journal PNAS.
The publication was led by Sian Kou-Giesbrecht from Simon Fraser University in Burnaby, Canada, as part of a working group on biological nitrogen fixation, of which Bettina Weber is a member. The working group is supported by the U.S. Geological Survey (USGS) John Wesley Powell Centre for Analysis and Synthesis.
“We compared different Earth System models with current nitrogen fixation values and found that they overestimate the nitrogen fixation rate on natural surfaces by about 50 per cent,” Weber explains. Overall, this overestimation of biological nitrogen fixation leads to a reduction in the CO2 fertilisation effect of about 11 per cent.
Weber therefore advocates revising the Earth System models in order to better assess developments. “This is because gases such as nitrogen oxides and nitrous oxide are produced as part of the nitrogen cycle. These can be released into the atmosphere through conversion processes and alter or disrupt climate processes.”