Agriculture

The Quality of Plants Is Declining Because of Climate Change

By Dr. Lewis Ziska

Balance is, without question, important in plant biology: Too much or too little sun, the right amount of rainfall, the right temperature range, and the necessary soil nutrients are critical to maintaining a healthy and diverse plant community.

But that stability is being threatened by climate change; in part because of peripatetic changes in climate, but even more by what is happening with carbon dioxide, the primary global warming gas. For the recent geological past (a couple million years, perhaps longer), there hasn’t been enough carbon dioxide in the air to maximize photosynthesis, growth, and yield for about 90 percent of all plant species. But now, BOOM, carbon dioxide levels are soaring, having risen 30 percent in my lifetime, and likely to rise another 50 percent by the end of the century — so very, very fast.

There are literally hundreds of published studies showing that recent and projected changes in carbon dioxide stimulate photosynthesis, growth, and yield for hundreds of plant species. CO₂ is plant food.

So, this is a good thing, yes? More CO₂, more plant growth, more food.

When you change a resource needed by plants, not every plant species responds the same way. If you are an avid gardener, try this: Dump lots of fertilizer in your garden, and tell me what responds more, weeds or flowers?

Dump lots of fertilizer in your garden, and tell me what responds more, weeds or flowers?

Let’s apply the fertilizer example to CO₂. If I add more CO₂ to a field of rice, we have found that rice responds a little, but weeds in the field respond a lot, lowering the yield of rice. What if I add more CO₂ to a natural ecosystem? Well, again, some plants, often invasive weeds like kudzu, can respond much more to the new resource, to their benefit, but to the detriment of other plant species, and in time, to biodiversity. To assume that more CO₂ automatically translates to increases in plants that only humans desire reflects a desperate and dogmatic ignorance of how plants and plant communities function.

There’s more. It’s not just plant growth that’s off-balance from rising carbon dioxide: so is plant chemistry. Plants do not live by carbon alone. They need other nutrients, especially nitrogen, to make the amino acids, proteins necessary for human growth and development.

But these nutrients — nitrogen, phosphorous, potassium, etc. — come from the soil. And herein lies a dilemma: While carbon, as carbon dioxide, is rapidly increasing in the atmosphere, soil nutrients haven’t changed. This leads to a fundamental, and global, imbalance.

How does such an imbalance affect us? As carbon increases and other nutrients remain the same, plants are prioritizing. Plants may be growing faster, but are, in general, of poorer quality. For example, nitrogen is fundamental to making proteins, but as nitrogen declines relative to carbon, proteins are declining. Plant vitamins that require a lot of nitrogen (e.g. vitamin B9 from rice) may be decreasing in concentration. Secondary chemicals like nicotine and caffeine that are rich in nitrogen — their concentration may also be declining. But if I have a secondary chemical that doesn’t need nitrogen, but lots of carbon, (e.g., vitamin E), its concentration may be going up.

Plants may be growing faster, but are, in general, of poorer quality.

So, basically, all plant life, all of what makes living possible, the global food chain, is being directly affected by the increase in carbon dioxide — aside from climate change. Is CO₂ plant food? Yes, some species may be stimulated in growth, but the secondary effects, from food production (crop vs. weed responses) to plant communities and biodiversity (kudzu rules!) are of deep concern.

If you find these plant biological changes too esoteric, too remote, then think of it from a personal space. What you are putting in your mouth, now and for the rest of the century, may be carbon-rich and nutrient-poor. And the consequences for human nutrition, and human health (not to mention plant ecology), are only now beginning to be examined — during a pandemic and an administration that denies climate change.

Lewis H. Ziska is an Associate Professor in Environmental Health Sciences at the Mailman School of Public Health at Columbia University. His latest book, Agriculture, Climate Change and Food Security in the 21st Century: Our Daily Bread, Cambridge Scholars Publishing, is available on Amazon.

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