Is there anything that carbon dioxide can’t do? https://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511
If you read the linked article, you come away with the idea that carbon dioxide is making our vegetable and grains (other than corn) less nutritious. That may be true, but it is also irrelevant. Plants have two systems that are necessary for growth, roots and leaves. The leaves are the part that catches carbon dioxide via osmosis of gas and turns it into carbohydrates via photosynthesis, and adding CO2 to the atmosphere makes it easier for the leaves to do their job. The roots on the other hand, work through liquid osmosis, and the environment that they find themselves in determines just how many minerals are available for uptake.
With me so far? Good.
To restate, and make it plainly obvious, it makes complete sense that mineral uptake lags behind carbohydrate generation when there is more atmospheric carbon dioxide without an increase in aqueous mineral content available to the root system.
Plants use carbohydrates to form the bulk of their structural tissues. This means with more carbohydrates plants can grow faster. Faster growth without an increase in aqueous mineral content means that a larger plant will grow under enriched CO2 conditions, but have the same mineral content as a plant grown under normal conditions. This is a “dilution effect” because the mineral content of the entire plant doesn’t change, but the volume of the plant does.
If you grow a plant 8% larger through CO2 enrichment (artificial or not), you logically expect it to have 8% less mineral density. That we only eat a certain part of most plants, the fruit, stalk, root, or leaf, means that we are getting less mineral density per serving (because we aren’t increasing our serving size 8% to account for the mineral difference).
Now, all of this is “interesting” but irrelevant, especially if you are an omnivore. Three oysters will generally generally satisfy your daily requirement for zinc. An 8oz beef steak covers zinc and around half your iron requirement. If you are a vegan vegetarian, you’ll NEVER get enough iron from “natural” food, you will need supplementation to remain healthy (even the medical journal of Australia points out that iron fortification of cereals is recommended for vegetarians to maintain adequate iron intake).
The reason why we use mineral salt licks in raising cattle is to ensure that they get enough minerals fast enough to support growth and health. In Australia, there was a mysterious growth and health issue with cattle that was fixed by giving them mineral salt licks instead of standard salt licks. Originally the scientists thought it was an iron deficiency, but through feed analysis it turned out that it wasn’t iron, but cobalt. The only form of cobalt your body needs is as part of Vitamin B12, which is produced by the gut bacteria of ruminants (cows, goats, sheep, etc). The minute trace amounts of cobalt in the mineral salt licks were enough to get the cattle back into health, despite their grazing range being essentially devoid of cobalt.
So I don’t worry about the potential decrease in mineral content of tomatoes, potatoes, or wheat. As long as the plants are getting enough for them to grow, they will grow. If someone is REALLY CONCERNED about vegetable mineral nutrient density, they’ll need to start mineralizing the soil to create more aqueous minerals for plant uptake by the root system. Otherwise there is nothing to do but keep eating a variety of foods in order to maintain your health.