The world’s forests are vital in the fight against climate change, as they absorb around a quarter of the greenhouse gases released into the atmosphere. Trees need carbon atoms to grow and thus provide us humans with an ecosystem service by absorbing large amounts of carbon dioxide from the air.
When greenhouse gas concentrations rise, trees and other plants can also contribute further by stepping up their photosynthesis. Thanks to this increase in production in the photosynthetic factory, trees can thus grow faster than normal by storing even more carbon. This phenomenon is known as carbon dioxide fertilisation.
In a new study, researchers have investigated the effects of carbon dioxide fertilisation and the extent to which this effect could help in reducing greenhouse gas levels in the atmosphere into the future.
“For carbon dioxide fertilisation to work, trees need nutrients such as phosphorus and nitrogen from the soil,” says Benjamin Smith, professor of ecosystem science at the Department of Earth and Environmental Sciences, Lund University, and one of the researchers behind the study.
More difficult for the forest
The results point to unexpected complexity in the balance between the various processes involved. In the computer simulations, the trees demonstrate an ability to switch between phases where growth accelerates due to carbon dioxide fertilisation and phosphorus fertilisation, respectively. However, more phosphorus does not in itself lead to stronger carbon dioxide fertilisation, which surprised the researchers.
This means that in many forests a continued increase in the uptake of greenhouse gases in the coming decades is unlikely. Large swathes of the forests in the tropics and in dry regions around the world are believed to be phosphorus-limited, meaning that these extensive areas naturally suffer from a lack of phosphorus in the soil.
– Ultimately, it is even more important for the global community to tackle emissions. We cannot rely on forests to prevent excessively high levels of greenhouse gases and ever-increasing global warming,” says Benjamin Smith.
The study has recently been published in the scientific journal Proceedings of the National Academy of Sciences:
“Phosphorus enrichment does not enlarge the predicted CO2 fertilisation effect on forest carbon sequestration”