As Carbon Dioxide Goes Up, Plants’ grow faster, but Nutrient Content Declines

More scaremongering about CO2 in the atmosphere! So plants grow faster and larger with more CO2, but with less quality? I have some doubts as to the claimed nitrogen reduction and its cause.

Let's keep in mind that CO2 is a trace gas measured in a few hundred parts per million! There are some serious doubts as to whether the increase of CO2 over the least 3 million years was so "unprecedented" as claimed.

It is also noteworthy that the article investigates only one of three ways of carbon fixation in plants, i.e. C3.

"As greenhouse gas concentrations in the air continue to climb, plants are faced with a veritable feast of carbon dioxide, which they use alongside water and sunlight to photosynthesize. While years of research shows that this profusion of carbon allows some plants to grow faster and larger, a literature review published today (November 3) in Trends in Plant Science indicates that the full story is far less encouraging. ...
On one hand, the boosted photosynthesis and consequently heightened carbohydrate production ups the biomass of C3 plants, a group that contains the vast majority of vegetation on Earth. But multiple studies suggest that these plants, which include major agricultural crops, take in less nitrogen as a result of that excess carbon, thereby reducing their nutritional value and their ecosystems’ capacities to act as carbon sinks. ..."

From the abstract:

"The elevation of atmospheric CO2 concentration has a strong impact on the physiology of C3 plants, far beyond photosynthesis and C metabolism. In particular, it reduces the concentrations of most mineral nutrients in plant tissues, posing major threats on crop quality, nutrient cycles, and carbon sinks in terrestrial agro-ecosystems. The causes of the detrimental effect of high CO2 levels on plant mineral status are not understood. We provide an update on the main hypotheses and review the increasing evidence that, for nitrogen, this detrimental effect is associated with direct inhibition of key mechanisms of nitrogen uptake and assimilation. We also mention promising strategies for identifying genotypes that will maintain robust nutrient status in a future high-CO2 world."

From the paper:

"The continuous elevation of atmospheric CO2 concentration ([CO2]atm) since the preindustrial era (from ~280 to ~415 ppm) has been unprecedented in both rate and amplitude over the past 3 million years. ..."

As Carbon Dioxide Goes Up, Plants’ Nutrient Content Declines | The Scientist Magazine® Abundant environmental CO2 can increase plant biomass and photosynthesis, but it has downsides for agriculture and ecosystems, a growing body of research finds.

The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal (open access)

Figure 1 Main hypotheses to explain the negative impact of elevated [CO2] (eCO2) on the mineral composition and especially on N content of C3 plants.