What if plants stopped feeding us?

"Eat five fruits and vegetables a day. A slogan that could well become a has-been in the years to come. The cause? The deterioration in the nutritional quality of plants as a result of rising CO2 concentrations in the atmosphere. A phenomenon that is still poorly understood, and which researchers at the Montpellier laboratory of plant biochemistry and molecular physiology.

"In 50 years' time, the increase in CO2 levels, which we can no longer control, will probably significantly boost agricultural production, but this production will be of lower nutritional quality. This is the alarming observation shared by Alain Gojon, researcher at the Plant Biochemistry and Molecular Physiology Laboratory.

A global food challenge

Everything had started well. For once, the rising concentration of CO2 in the atmosphere, caused by human activity and responsible, among other things, for global warming, was having a positive effect. It stimulated the growth of numerous plant species by boosting their photosynthesis. Photosynthesis," explains Alain Gojon, "is the ability of plants to make sugars with CO2, light and water. It's the basis of the food chain of life.

In the 90s, researchers began to see the dual hope of boosting global food production while sequestering excess CO2. It's one of the possible solutions to the food challenge facing the planet," says Alain Gojon. There will be 9 billion of us by 2050, and more than 10 billion by the end of the century. We're going to have to feed everyone. Initial calculations based on projected CO2 increases point to a 40% rise in agricultural production. A windfall.

Less minerals but more sugar

Over 2,600 experiments have been carried out to test this prediction. These experiments, called FACE for free air CO2 enrichment, involve reproducing an artificial CO2 bubble on field crops, using a system of nozzles to continuously inject carbon dioxide. Hundreds of plant species, including wheat, tomatoes, rice, potatoes and beans, have been tested worldwide. "The first publications came out as early as 1998, but it's only in the last 3 or 4 years that we've had summaries of all these experiments. The result is two conclusions.

First of all, the gain in agricultural productivity, which in the end was much less than the researchers had hoped. " We're closer to 10% than 40%," says Alain Gojon. Secondly, and unexpectedly, there was a significant loss of the mineral elements and proteins contained in these plants grown under CO2: "The loss of nitrogen, which is a major constituent of proteins, is around 15%. For minerals such as phosphorus, potassium, calcium, magnesium and iron, it's minus 10%.
Recent studies on rice varieties even report a vitamin loss of up to 40%. On the other hand, they contain more sugar, since their carbon content is higher.

Serious health consequences

Within the next fifty years, the plants we eat could be richer in energy but poorer in essential nutritional elements, with potentially serious consequences for the human population.
"A recent study indicates that 120 million more people worldwide will suffer from protein deficiency, and an additional 1.5 billion women and children will suffer from aggravated anemia due to iron deficiency. Once again, it's the South that will pay the highest price. In the North," continues the researcher, " the nutritional imbalance could translate into a rise in obesity and overweight due to the increased sugar content of plants." To gain a better understanding of this phenomenon, the QualiSud laboratory will be analyzing changes in the nutritional quality of foods produced under high CO2 in order to measure their impact on human health.

This process could already be underway, as researchers comparing contemporary wild plants with samples taken from pre-industrial herbariums have found that the mineral content of the same species is already lower. The problem," continues Alain Gojon, "is that nothing we currently know about the physiology of plant mineral nutrition allows us to explain this. And that's what's at stake in the research that will begin in Montpellier in January 2019.

Two hypotheses

"The first hypothesis is that, for some reason that we don't understand, the increase in CO2 affects the functioning of plants, which are then less efficient at extracting mineral elements from the soil. The second, on which the Eco&Sol laboratory in Montpellier will be working in association with Alain Gojon's team, is that "CO2 could have an effect on the functioning of biogeochemical cycles of elements in the soil. The idea is that plants may still function just as well, but there are fewer mineral elements available to them in the soil".

By verifying these hypotheses, the researchers hope not only to understand this mechanism, but perhaps also to find solutions to this future crisis. "Thanks to the unique facilities available at theMontpellier Ecotron, we will be using 140 plant lines to try to identify the genetic determinants of the negative impact of high CO2 on plant nutritional quality.
With the hope perhaps of producing plant varieties less impacted by rising CO2.