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Rising carbon dioxide levels affect nutrients in crops

basic food plants will carry lower concentrations of iron and zinc

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robert99 robert99 Sweden Posts: 1360
1 21 Mar 2018
http://www.latimes.com/science/sciencenow/la-sci-sn-carbon-dioxide-crops-20140507-story.html

The increased concentration of carbon dioxide that comes with climate change could mean some basic food plants will carry lower concentrations of iron and zinc – and deficiencies of those nutrients are already a "substantial global public health problem," scientists reported Wednesday.

The scientists studied grains and legumes grown at the elevated atmospheric concentrations of carbon dioxide predicted for the middle of this century. They conducted a meta-analysis of data from their own study and previous ones, looking at 143 comparisons of the edible portions of crops at both ambient levels of carbon dioxide and elevated levels of 546 to 586 parts per million.

Carbon dioxide in the atmosphere is expected to reach 550 ppm in the next four to six decades. The lead scientist on the study, Samuel Myers of the Harvard School of Public Health, said by telephone that the issue should be of concern to people no matter their views on climate change.

The work was done at seven sites in Japan, Australia and the United States. The scientists tested rice, wheat, maize, soybeans, field peas and sorghum over several growing seasons.

"We found that elevated carbon dioxide was associated with significant decreases in the concentrations of zinc and iron," the researchers said in the journal Nature.

The wheat had 9.3% lower zinc and 5.1% lower iron at the elevated levels, for example. And the protein content was 6.3% lower in wheat and 7.8% lower in rice, the researchers reported. Maize and sorghum had no significant change, and there was a small decrease in protein in field peas, they said.

"[W]e find that the edible portions of many of the key crops for human nutrition have decreased nutritional value when compared with the same plants grown under identical conditions but at the present ambient" carbon dioxide, the researchers said.

An estimated 2 billion people are deficient in zinc and iron, leading to a loss of 63 million life-years annually, the scientists said. And, according to the United Nations Food and Agriculture Organization, 2.3 billion people live in countries where at least 60% of the dietary zinc and iron comes from the affected grains and legumes.

Decreases in protein, the researchers said, could lead to increased risk of hypertension, heart disease and other problems.

The major micronutrient deficiencies globally are iron, zinc and vitamin A, Myers said. Vitamin A generally comes from produce, and he said he didn't know of any efforts to look at effects on it of elevated carbon dioxide.
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robert99 robert99 Sweden Posts: 1360
2 22 Mar 2018
https://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511

In the outside world, the problem isn’t that plants are suddenly getting more light: It’s that for years, they’ve been getting more carbon dioxide. Plants rely on both light and carbon dioxide to grow. If shining more light results in faster-growing, less nutritious algae—junk-food algae whose ratio of sugar to nutrients was out of whack—then it seemed logical to assume that ramping up carbon dioxide might do the same. And it could also be playing out in plants all over the planet. What might that mean for the plants that people eat?

What Loladze found is that scientists simply didn’t know. It was already well documented that CO2levels were rising in the atmosphere, but he was astonished at how little research had been done on how it affected the quality of the plants we eat. For the next 17 years, as he pursued his math career, Loladze scoured the scientific literature for any studies and data he could find. The results, as he collected them, all seemed to point in the same direction: The junk-food effect he had learned about in that Arizona lab also appeared to be occurring in fields and forests around the world. “Every leaf and every grass blade on earth makes more and more sugars as CO2 levels keep rising,” Loladze said. “We are witnessing the greatest injection of carbohydrates into the biosphere in human history―[an] injection that dilutes other nutrients in our food supply.”

He published those findings just a few years ago, adding to the concerns of a small but increasingly worried group of researchers who are raising unsettling questions about the future of our food supply. Could carbon dioxide have an effect on human health we haven’t accounted for yet? The answer appears to be yes—and along the way, it has steered Loladze and other scientists, directly into some of the thorniest questions in their profession, including just how hard it is to do research in a field that doesn’t quite exist yet.

IN AGRICULTURAL RESEARCH, it’s been understood for some time that many of our most important foods have been getting less nutritious. Measurements of fruits and vegetables show that their minerals, vitamin and protein content has measurably dropped over the past 50 to 70 years. Researchers have generally assumed the reason is fairly straightforward: We’ve been breeding and choosing crops for higher yields, rather than nutrition, and higher-yielding crops—whether broccoli, tomatoes, or wheat—tend to be less nutrient-packed.

In 2004, a landmark study of fruits and vegetables found that everything from protein to calcium, iron and vitamin C had declined significantly across most garden crops since 1950. The researchers concluded this could mostly be explained by the varieties we were choosing to grow.

Loladze and a handful of other scientists have come to suspect that’s not the whole story and that the atmosphere itself may be changing the food we eat. Plants need carbon dioxide to live like humans need oxygen. And in the increasingly polarized debate about climate science, one thing that isn’t up for debate is that the level of CO2 in the atmosphere is rising. Before the industrial revolution, the earth’s atmosphere had about 280 parts per million of carbon dioxide. Last year, the planet crossed over the 400 parts per million threshold; scientists predict we will likely reach 550 parts per million within the next half-century—essentially twice the amount that was in the air when Americans started farming with tractors.

If you’re someone who thinks about plant growth, this seems like a good thing. It has also been useful ammunition for politicians looking for reasons to worry less about the implications of climate change. Rep. Lamar Smith, a Republican who chairs the House Committee on Science, recently argued that people shouldn’t be so worried about rising CO2 levels because it’s good for plants, and what’s good for plants is good for us.

“A higher concentration of carbon dioxide in our atmosphere would aid photosynthesis, which in turn contributes to increased plant growth,” the Texas Republican wrote. “This correlates to a greater volume of food production and better quality food.”

But as the zooplankton experiment showed, greater volume and better quality might not go hand-in-hand. In fact, they might be inversely linked. As best scientists can tell, this is what happens: Rising CO2 revs up photosynthesis, the process that helps plants transform sunlight to food. This makes plants grow, but it also leads them to pack in more carbohydrates like glucose at the expense of other nutrients that we depend on, like protein, iron and zinc.
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