Study Reveals Drop in Fertilizing Effect of Excess CO2 on Vegetation Worldwide

Plants tend to remove CO₂ from the air when they absorb it for their growth. Thus, CO₂ gets sequestered in their roots, trunk, or branches.

An article published recently in the journal Science demonstrates that this fertilizing impact of CO₂ is reducing globally, as per the study co-directed by Professor Josep Peñuelas of the CSIC at CREAF and Professor Yongguan Zhang of the University of Nanjin, with the contribution of CREAF scientists Jordi Sardans and Marcos Fernández.

The study performed by an international team suggests that the decrease has reached 50% progressively from 1982 mainly due to two factors: the availability of nutrients and water.

There is no mystery about the formula, plants need CO₂, water and nutrients in order 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.

Josep Peñuelas, Professor, Spanish National Research Council

Three years ago, Professor Peñuelas already reported in an article in Nature Ecology and Evolution that the fertilizing impact of CO₂ would not go on forever and that plants cannot grow endlessly, since there are other factors restricting them.

If there is a drop in the fertilizing capacity of CO₂, there will be major impacts on the carbon cycle and thus on the climate. For several decades, forests have obtained a veritable CO₂ bonus, which has enabled them to sequester tons of carbon dioxide that allowed them to increase photosynthesis and grow further. In fact, this elevated sequestration has been able to decrease the CO₂ accumulated in the air, but this has now dropped.

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 climate change mitigation strategies and policies at the global level. Nature’s capacity to sequester carbon is decreasing and with it society’s dependence on future strategies to curb greenhouse gas emissions is increasing.

Josep Peñuelas, Professor, Spanish National Research Council

Published in the Science journal, the study has been performed using atmospheric, satellite, ecosystem, and modeling data. It emphasizes the use of sensors based on near-infrared and fluorescence and are hence capable of quantifying vegetation growth activity.

Less Water and Nutrients

The findings show that the absence of water and nutrients are the two factors that decrease the capacity of CO₂ to enhance plant growth. To arrive at this conclusion, the researchers studied data that was obtained from hundreds of forests analyzed over the past four decades.

“These data show that concentrations of essential nutrients in the leaves, such as nitrogen and phosphorus, have also progressively decreased since 1990,” explained researcher Songhan Wang, the first author of the study.

The team has discovered that the availability of water and the temporal variations in water supply play an important 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.

Yongguan Zhang, Researcher, University of Nanjin

Journal Reference:

Wang, S., et al. (2020) Recent global decline of CO₂ fertilization effects on vegetation photosynthesis. Science. doi.org/10.1126/science.abb7772.