New study solves old climate mystery about ecosystems’ nutrient limitation

Forest and sky. Photo.

The ability of global ecosystems to absorb carbon dioxide is regulated to a large extent by the nutrients nitrogen and phosphorus. With lower plant access to these nutrients, greater volumes of carbon dioxide stays in the atmosphere, instead of being absorbed by forests and other ecosystems. A new study has now charted the global patterns of this nitrogen and phosphorus limitation.

Plants need water, sunlight and carbon dioxide in order to grow. They also need nutrients such as nitrogen and phosphorus. With unlimited access to nutrients, plants can grow faster and thereby absorb more carbon dioxide from the atmosphere. In an international study, now published in the research journal Nature Geoscience, the researchers have focused on how nitrogen and phosphorus affect different ecosystems’ carbon dioxide uptake around the world.

“A better understanding of how ecosystems are limited by different nutrients means that we can estimate if today’s carbon dioxide uptake will continue or decline in the future”, says Anders Ahlström, physical geography researcher at Lund University.

By bringing together 171 ecosystem studies that measure how plants resorb nitrogen and phosphorus when their leaves fall in the autumn, or before a dry period, the researchers could go on to map the nitrogen and phosphorus limitation globally. After quantification work and extensive meta-analyses, new nitrogen and phosphorus maps of the world could be drawn. The new study shows that 43 per cent of the world’s ecosystems’ are limited by phosphorus. Only 18 per cent is limited by nitrogen, whereas 39 per cent of the global, forest-related carbon dioxide uptake is limited equally by nitrogen and phosphorus.

World map with red and blue fields. Illustration.
Researchers have created nitrogen and phosphorus maps of the world.
Researchers have created nitrogen and phosphorus maps of the world.

“Phosphorus is a nutrient that is finite and mined. In step with the increasing use of biomass globally, it could be the case that phosphorus becomes an increasingly limiting factor for vegetation carbon dioxide uptake. In the long term, this may contribute to higher levels of carbon dioxide in the atmosphere and a faster rate of climate change”, says Anders Ahlström.

The study was led by researchers at Beijing Normal University and Stanford University with Lund University, Utrecht University and the Chinese Academy of Sciences participating in the work.

The new study was published in the research journal Nature Geoscience.

Study: "Global patterns of terrestrial nitrogen and phosphorus limitation" -