🌱 Climate: plants may absorb less carbon than expected

Considered natural allies against climate change due to their absorption of carbon dioxide, plants may however offer more limited help than expected. The cause: an essential element: nitrogen.

Indeed, when CO2 increases in the atmosphere, it can stimulate plant growth, a phenomenon called the fertilization effect. However, this growth requires nitrogen, a key nutrient that plants must draw from the soil. Without sufficient supply, their development is limited, which reduces their ability to capture carbon. Consequently, the climate benefit of plants closely depends on the availability of this element.


Published in PNAS, an international study reveals that climate models have overestimated natural nitrogen fixation. This process, where microorganisms transform atmospheric nitrogen into a form usable by plants, is fundamental to the ecosystem. Researchers compared several Earth system models with current data, discovering an overestimation of about 50%.

This overestimation has direct consequences on climate forecasts. It leads to a reduction of about 11% in the CO2 fertilization effect, meaning that plants would absorb less carbon than expected. Consequently, projections on the slowing of warming could be too optimistic, requiring adjustments in the models used to assess trends.

The proposed revisions are important because they affect gases such as nitrogen oxides, which can influence the climate. By improving the accuracy of models, scientists hope to better understand the interactions between carbon and nitrogen cycles. This would allow refining strategies to mitigate climate changes, taking into account the real limits of ecosystems.

This research highlights the importance of accurate nutrient data in climate models. With more accurate information on nitrogen fixation, forecasts could become more reliable.

The nitrogen cycle

Nitrogen is an abundant element in the atmosphere, but in a form that plants cannot use directly. To become available, it must be fixed by bacteria or other microorganisms present in the soil or associated with certain plants. This biological fixation process transforms gaseous nitrogen into compounds such as ammonia, which are absorbable by plants.

Once in the soil, nitrogen follows a cycle involving the decomposition of organic matter and transformation by microbes. Plants absorb it through their roots to support their growth, particularly in the production of proteins and chlorophyll. After their death, nitrogen returns to the soil, completing the cycle and maintaining ecosystem fertility.

This cycle is essential for the productivity of natural and agricultural ecosystems. Any disturbance can affect plant growth and their ability to sequester carbon.