Even as carbon dioxide increases in the atmosphere, mature, nutrient-limited forests will not absorb it, according to a new study. Not only will adult trees not accumulate more carbon, they will return it to the atmosphere. This finding shows that the only strategy to limit climate change is to reduce greenhouse gas emissions.
A higher amount of CO2In the atmosphere does not invariably imply a greater carbon sequestration by trees, thus offsetting part of the increase in carbon dioxide that we produce on Earth, contrary to what was thought up to now. This is demonstrated by a study published in the journalNature, which reveals where that CO will actually go2More than our mature forests will receive.
The international team, led by the Institute for the Environment of Western Sydney University in Hawkesbury (Australia) and which has had Spanish participation, carried out an experiment in a native eucalyptus forest in Australia, artificially increasing the amount of CO2 you usually get.
In particular, the concentration was increased by 150 parts per million, which corresponds to an increase of 38% above the 400 parts per million in today's atmosphere. After this increase in CO2 the scientists monitored the fate of that carbon within the eucalyptus forest.
The results showed that growing and fertilized forest plantations sequester more carbon dioxide to obtain faster growth of young trees. However, the effects are not as positive when the experiment is carried out in mature forests.
In adult trees, this experimental increase in CO2It was not reflected in increased growth or accumulation in trees or in the soil, in the form of organic matter, for example. What did increase was the “respiration” of the soil itself, which resulted in a greater release of previously captured or accumulated carbon.
“An increase in CO2 Atmospheric does not have to result in increased carbon build-up in plants or soil. It could even happen that when the activity of soil communities accelerates due to a greater contribution of sugars by plants, part of the carbon accumulated in the ecosystem is released”, Explains Raúl Ochoa-Hueso, Ramón y Cajal researcher at the University of Cádiz and one of the authors of this research.
Along with him, Teresa E. Gimeno from the Basque Center for Climate Change and Ikerbasque and Juan Piñeiro from the University of West Virginia have participated.
How the soil breathes
Soil respiration is the sum of what all animals, plants, fungi and bacteria, among others, breathe. Many of these organisms live directly or indirectly from the decomposition of organic matter in the soil as well as the contributions of sugars released by the roots of the plants.
The function of these sugars is to promote the growth and activity of microorganisms that help to release nutrients from the soil that are essential for plants, such as phosphorus or nitrogen. These processes of decomposition of organic matter and respiration of sugars release CO2 to the atmosphere.
“Long-term exposure to high levels of carbon dioxide can only increase carbon storage in ecosystems with young trees or very fertile soils.”, Emphasizes Mingkai Jiang, lead author of the work and researcher at the Australian university.
Today we only depend on mature forests to absorb some of the additional carbon dioxide that we are emitting. "Our findings suggest that we have even less time than we think to reduce greenhouse gas emissionsJiang points out.
Although mature forests are an important carbon reservoir at a global level, the results of this study confirm that “the main strategy to limit global warming, within the objectives set out in the Paris Agreement, must be to reduce emissions of greenhouse gases into the atmosphere ”, concludes Ochoa-Hueso.
Mingkai Jiang et al. "The fate of carbon in a mature forest under carbon dioxide enrichment"Nature April 8, 2020.