Vegetation on earth has a key role in mitigating the climate crisis because it reduces the excess CO2 from the atmosphere that we humans emit. Just like when athletes are doped with oxygen, plants also benefit from the large amounts of CO2 that accumulate in the atmosphere. If more CO2 is available, they make more photosynthesis and grow more, which is called the fertilizing effect of CO2. When plants absorb this gas to grow, they remove it from the atmosphere and it is sequestered in the branches, trunk or roots.
An article published in Science, co-directed by the Professor of the Higher Council for Scientific Research at CREAF Josep Peñuelas and Professor Yongguan Zhang of the University of Nanjin, with the participation of CREAF researchers Jordi Sardans and Marcos Fernández, shows that this fertilizing effect of CO2 is decreasing worldwide.
The study, developed by an international team, concludes that the reduction has reached 50% progressively since 1982 due to two key factors: the availability of water and nutrients.
“The formula has no mystery, plants need CO2, water and nutrients to grow. However much the CO2 increases, if the nutrients and water do not increase in parallel, the plants will not be able to take advantage of the increase in this gas,” explains Professor Josep Peñuelas. In fact, three years ago he himself warned in an article in Nature Ecology and Evolution that the fertilizing effect on the soil would not last forever, that plants cannot grow indefinitely because there are other factors that limit them.
If the fertilizing capacity of CO2 in the soil decreases, there will be strong consequences on the carbon cycle and therefore on the climate. Forests have been ‘doped’ with the extra CO2 for decades, sequestering tons of carbon dioxide that allowed them to do more photosynthesis and grow more. In fact, this increased fixation has managed to decrease the accumulated CO2 in the air, but now it is over.
“These unprecedented results indicate that the absorption of carbon by vegetation is beginning to become saturated. This has very important climate implications that must be taken into account in possible strategies and policies to mitigate climate change at the global level. Nature decreases its capacity to sequester carbon and with it increases society’s dependence on future strategies to curb greenhouse gas emissions,” warns Peñuelas.
The study has been carried out with satellite, atmospheric, ecosystem and modeling information. It highlights the use of sensors that use near infrared and fluorescence and are thus able to measure the growth activity of vegetation.
Less water and nutrients
According to the results, the lack of water and nutrients are the two factors that reduce the ability of CO2 to improve plant growth in the soil. To reach this conclusion, the team based itself on data obtained from hundreds of forests studied over the past forty years. “These data show that the concentrations of essential nutrients in the leaves, such as nitrogen and phosphorus, have also decreased progressively since 1990,” explains researcher Songhan Wang, first author of the article.
The team also found that water availability and temporary changes in water supply played a significant role in this phenomenon. “We have found that plants slow down their growth, not only in times of drought, but also when there are changes in the seasonality of rainfall, which is increasingly happening with climate change,” adds Yongguan Zhang.