Does CO2 make food less nutritious?

In recent years, studies have found that our food is becoming less nutritious [1,6,11]. Numbers vary between different crops [14], but there is a general pattern that a kilogram of crop grown recently has slightly lower levels of protein, calcium, iron, and other nutrients [1]. Why?

This is thought to not be due to changes in nutrients in the soil [2]. Neither is it due to human modification of the crops [3]. Over thousands of years, farmers have bred crops to be better in many ways – faster growing, more tasty, etc. [8]. This so-called “selective breeding” has in fact done the opposite – it has made crops better at taking up nutrients from the soil, and made them more rich in nutrients [9].

So what is going on? In fact, the nutrients in fruit and veg are thought to simply been diluted [2]. To grow, plants take CO2 and water, and combine them to make organic matter (sugars) and oxygen – this is photosynthesis [10]. Today, there is around 1.5x as much CO2 in the air than 100 years ago [3]. This is allowing some plants to grow faster [4,9]. However, plants are not necessarily able to take up extra nutrients to keep up with their faster growth rate [9]. So, the nutrients are spread throughout the plant, and per kilogram of crop, you get less nutrients [5].

The lower nutrient content of plants could cause nutritional deficiencies for people [7,11]. For example, you may need to eat more green veg to get enough iron [11,12]. It might be a problem for other animals, such as bees [5]. The pollen of flowers is becoming less protein-rich, meaning bees are getting less protein, making them weaker and more vulnerable to attack from disease, pesticides, and other insects [5]. There can also be more complicated effects: if a plant is less nutritious, then some insects will eat more of it to get enough nutrients, meaning greater crop losses to insects [13,14]. Some other insects may choose to eat different plants instead, reducing crop losses [14]. So, the effects of higher CO2 on plants are pretty complicated and unpredictable!

References

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