This article seems like much Ado about nothing. My guess is that human selective breeding of plants has far more impact than the effect the article discusses.
How would selective breeding affect the relative concentration / dilution of nutrients due to increased CO2?
It seems to be that the CO2 issue directly affects the inputs, making one input far more abundant than it used to be. To the degree that plants were constrained by CO2 as input, it logically leads to dilution of nutrients - unless you specifically bred plants that grew slower and produced lower yields, which seems unlikely.
(The actual mechanism, around plant's self-regulating water management affecting how much it retains vs needs to take in via the ground, is unlikely to be bred for one way or another.)
Surely selective breading may bring harm. For example, tinkering with wheat to make it easy to process with machines resulted in kinds where gluten is less tolerant by humans [1].
What is important is speed and scale. I.e. making most plants less nutritional by 5-10% within 50 years is something very new.
It seems to be that the CO2 issue directly affects the inputs, making one input far more abundant than it used to be. To the degree that plants were constrained by CO2 as input, it logically leads to dilution of nutrients - unless you specifically bred plants that grew slower and produced lower yields, which seems unlikely.
(The actual mechanism, around plant's self-regulating water management affecting how much it retains vs needs to take in via the ground, is unlikely to be bred for one way or another.)