A warmer planet, less nutritious plants and… fewer grasshoppers?
A warmer planet, less nutritious plants and… fewer grasshoppers?
Enlarge / A two-banded grasshopper in Markham, Ontario, Canada.
Creative Touch Imaging Ltd./NurPhoto via Getty Images
It's tough on a hungry grasshopper on the Kansas prairie. Oh, there's plenty of grass to eat, but the grass of this century isn't what it used to be. It is less nutritious, deficient in minerals like iron, potassium and calcium.
Partly because of this nutrient-poor diet, there has been a huge drop in grasshopper numbers in recent times, by around a third over two decades, according to a 2020 study. before, and the main culprit is carbon dioxide, according to study author Michael Kaspari, an ecologist at the University of Oklahoma at Norman.
Atmospheric carbon dioxide is at its highest level in human history. This is probably good for plants like grasses that hoppers nibble on. They can turn that atmospheric carbon into carbohydrates and build more plants. In fact, plant biologists once thought that all that extra carbon dioxide would just mean better crop yields. But experiments on crops exposed to high levels of carbon dioxide indicate that many food plants contain fewer other nutrients than under the carbon dioxide concentrations of the past. Several studies show that nitrogen levels in plants, for example, have decreased, indicating lower plant protein content. And some studies suggest that plants can also be deficient in phosphorus and other trace minerals.
The idea that plants grown in today's carbon dioxide-rich era will contain less of certain other elements (a concept Kaspari refers to as nutrient dilution) has been well studied in crop plants. Nutrient dilution in natural ecosystems is less studied, but scientists have observed it in many places, from the woods of Europe to the kelp forests off Southern California. Now researchers like Kaspari are beginning to look at the training effects, to see if herbivores that eat these plants, such as grasshoppers and grazing mammals, are affected.
The scant data already available suggests that nutrient dilution could cause widespread problems. “I think we are in canary territory in a coal mine,” says Kaspari.
Lower quality food?
It is clear that increased levels of carbon dioxide alter the composition of plants in various ways. Scientists have conducted years-long studies in which they pump carbon dioxide onto crops to artificially increase their exposure to the gas, then test the plants for nutrient content. A large analysis found that increasing carbon dioxide by about 200 parts per million increased plant mass by about 18%, but often reduced nitrogen, protein, zinc and iron levels.
Vegetables like lettuce and tomatoes may be sweeter and tastier due to the added carbon-rich sugars, but lose about 10-20% of the protein, nitrates, magnesium, iron, and zinc they contain in low carbon conditions. , according to another large study. On average, plants can lose about 8% of their mineral content under high carbon dioxide conditions. Kaspari likens the effect to swapping a hearty kale salad for a bowl of nutrient-poor iceberg lettuce.
Enlarge / A two-banded grasshopper in Markham, Ontario, Canada.
Creative Touch Imaging Ltd./NurPhoto via Getty Images
It's tough on a hungry grasshopper on the Kansas prairie. Oh, there's plenty of grass to eat, but the grass of this century isn't what it used to be. It is less nutritious, deficient in minerals like iron, potassium and calcium.
Partly because of this nutrient-poor diet, there has been a huge drop in grasshopper numbers in recent times, by around a third over two decades, according to a 2020 study. before, and the main culprit is carbon dioxide, according to study author Michael Kaspari, an ecologist at the University of Oklahoma at Norman.
Atmospheric carbon dioxide is at its highest level in human history. This is probably good for plants like grasses that hoppers nibble on. They can turn that atmospheric carbon into carbohydrates and build more plants. In fact, plant biologists once thought that all that extra carbon dioxide would just mean better crop yields. But experiments on crops exposed to high levels of carbon dioxide indicate that many food plants contain fewer other nutrients than under the carbon dioxide concentrations of the past. Several studies show that nitrogen levels in plants, for example, have decreased, indicating lower plant protein content. And some studies suggest that plants can also be deficient in phosphorus and other trace minerals.
The idea that plants grown in today's carbon dioxide-rich era will contain less of certain other elements (a concept Kaspari refers to as nutrient dilution) has been well studied in crop plants. Nutrient dilution in natural ecosystems is less studied, but scientists have observed it in many places, from the woods of Europe to the kelp forests off Southern California. Now researchers like Kaspari are beginning to look at the training effects, to see if herbivores that eat these plants, such as grasshoppers and grazing mammals, are affected.
The scant data already available suggests that nutrient dilution could cause widespread problems. “I think we are in canary territory in a coal mine,” says Kaspari.
Lower quality food?
It is clear that increased levels of carbon dioxide alter the composition of plants in various ways. Scientists have conducted years-long studies in which they pump carbon dioxide onto crops to artificially increase their exposure to the gas, then test the plants for nutrient content. A large analysis found that increasing carbon dioxide by about 200 parts per million increased plant mass by about 18%, but often reduced nitrogen, protein, zinc and iron levels.
Vegetables like lettuce and tomatoes may be sweeter and tastier due to the added carbon-rich sugars, but lose about 10-20% of the protein, nitrates, magnesium, iron, and zinc they contain in low carbon conditions. , according to another large study. On average, plants can lose about 8% of their mineral content under high carbon dioxide conditions. Kaspari likens the effect to swapping a hearty kale salad for a bowl of nutrient-poor iceberg lettuce.
Enlarge / A two-banded grasshopper in Markham, Ontario, Canada.
Creative Touch Imaging Ltd./NurPhoto via Getty Images
