Climate change and plant nutrition

The dreaded Brussels sprouts. Image from author

I have such a distaste for Brussels sprouts. Growing up, my two brothers and I would be forced to eat them twice a week because our Mum would say “they’re high in zinc and good for you”. Well, Mum, research into the effects of rising CO2 levels and plant nutrition have found that it will negatively affect some crops and vegetables – including Brussels sprouts.

We are already seeing the negative effects of climate change on some plants. When I go for a walk-through Churchill National Park, one of my favourite trees (Eucalyptus radiata) are beginning to decline due to the increase in temperature.

It was been reported by some, how should I say, more conservative journalists and politicians, that the increase in CO2 is great for plants. That some crop yields such as grains are better than they have been for years. They’re partially correct, but they’re either ignoring or misrepresenting the research.

Photosynthesis – Not all plants do it the same

Light, water, and CO2 are the three ingredients for photosynthesis. Photosynthesis occurs over two stages. Stage one captures the light energy from the sun, and Stage two converts the light energy to carbohydrates.

In stage two, known as the Calvin Cycle, atmospheric CO2 is ‘fixed’ to carbohydrate molecules. This carbon fixing is how plants can help mitigate the negative effects of climate change.

It is in the Calvin Cycle where plants differ in their CO2 ‘fixing’ and plants are categorised as C3, C4, or CAM, depending on how they ‘fix’ their carbon.

In C3 plants the first product in the Calvin Cycle is a 3-carbon molecule, while the first product in C4 plants is a 4-carbon molecule (hence C3 C4).

C3 plants include some grasses, wheat, rice, legumes, and most common vegetables (including Brussels sprouts). The most common C4 crops are corn and sorghum.

Plant Nutrition

 Earlier research on the effect of increased levels of CO2 found that an increase in CO2 would mean an increase in plant growth and crop yields for all plants, regardless of how they ‘fix’ their carbon.

More recent research in Free-Air Concentration Enrichment (FACE) with elevated CO2 agreed with the previous research that there would be an increase in plant growth and crop yields of both C3 and C4 plants. This, however, comes at a cost of reduced levels of protein and nutrient density of C3 plants.

Rubisco is the enzyme that begins and finishes the Calvin Cycle in plants, and is the most abundant protein on earth. The increase in CO2 means that the regeneration of Rubisco is reduced, decreasing the protein levels of some plants.

In all C3 grasses and legumes, there will be a decrease in iron and zinc. Wheat will have reduced levels of zinc by 9% and protein by 6%. The protein concentration of rice will be reduced by 8%.

Developing countries where their major source of protein, zinc, and iron are grains and legumes will be the most negatively affected by the reduced nutrient levels.

It’s not all doom and gloom though.C4 plants evolved in tough and dry conditions and when there were high levels of atmospheric CO2, which is why the increased levels of CO2 does not appear to have a negative effect on the nutrition of these plants.

Corn and Brussels sprouts. Image from author