Plants and fruits are starting to lose their nutritional value

More than one-third of all animals on Earth, from beetles to cows to elephants, subsist on plant-based diets. Since plants are typically low in calories, herbivorous creatures can already find it challenging to get the energy they need. 

Now, as climate change affects growing conditions, some of the plant-based foods that animals rely on are losing some of their nutritional value.

Human activities continue to increase atmospheric carbon dioxide levels and raise global temperatures. In response, many plants in ecosystems around the world are growing faster. 

Some researchers refer to this phenomenon as the “greening of the Earth,” and it can potentially offset some greenhouse gas emissions by locking more carbon into plant matter.

However, there is a trade-off: these rapidly growing plants often pack fewer nutrients into each bite.

Plant quality and animal population declines

Together with her colleagues at the Smithsonian Institution, Ellen Welti studies how this type of nutrient dilution influences species across the food web – from tiny grasshoppers to giant pandas.

They suspect that long-term declines in plant quality may be a largely unnoticed factor in falling animal populations. 

These changes in plant nutrition aren’t as visually obvious as rising sea levels, nor are they sudden like hurricanes or extreme heatwaves. Nonetheless, they can have significant impacts over time.

If plants become less nutritious, herbivores may need more time to find and consume enough food, making them more vulnerable to predators and other hazards.

Inadequate nutrient intake can also reduce animals’ fitness, affecting their growth, reproduction, and survival.

Rising carbon and declining nutrients

Scientists have already shown that climate change is causing nutrient dilution in human food crops.

Decreases in important micronutrients, such as iron, zinc, magnesium, and copper, are a particular concern. Records of crop nutrient content reveal that these elements have declined over time.

For humans, the loss of iron, zinc, and protein in staple foods is expected to worsen in the coming decades as CO₂ concentrations climb.

Such deficiencies could significantly affect global health and survival, especially in regions that heavily depend on crops like rice and wheat, including parts of East and Central Asia.

The quality of livestock feed is also declining. Cattle, which already spend substantial time grazing, are finding it increasingly difficult to consume enough protein. 

Protein concentrations in grasses are dropping across rangelands, diminishing animals’ weight gains and costing producers money. Moreover, wild species aren’t immune to nutrient dilution either. 

Bamboo quality and panda health

Giant pandas, a culturally significant threatened species, rely entirely on bamboo.

Because pandas breed slowly and need extensive, uninterrupted bamboo forests for habitat, their existence is jeopardized by the conversion of land for agriculture and development.

Pandas may also become an emblem of the risks posed by nutrient dilution.

The giant panda is considered an “umbrella species,” so preserving its habitat benefits many other organisms sharing its environment. 

Notably, giant pandas consume large quantities of bamboo daily. Now, rising temperatures are reducing bamboo’s nutritional value and making it harder for the plant to survive.

Because bamboo is such an essential resource for pandas, any decline in its nutrients could affect panda health and population numbers.

Mixed outcomes for insects

Insects play vital roles in pollination, serve as food sources for birds and animals, and fulfill other ecological functions.

Yet many insect species worldwide are in decline, including in places less affected by direct human activities. Shifts in plant chemistry may be influencing these declines.

Numerous insects are plant feeders and thus likely to be influenced by reduced plant nutritional quality.

Experiments have shown that when carbon dioxide levels go up, certain insect populations decrease, at least partly due to lower food quality.

However, not all insects respond similarly. Leaf-chewing insects, such as grasshoppers and caterpillars, appear most vulnerable, experiencing smaller body sizes and diminished reproduction. 

Conversely, locusts thrive on plants rich in carbon and might flourish under elevated CO₂ conditions. Insects like aphids and cicadas, which feed on phloem rather than leaves, could also benefit from carbon-rich plant structures.

Plant quality and struggling animals

Communities that are already nutrient-poor – like the ancient soils of Australia and the Amazon and Congo tropical basins – stand to be the most affected, since the animals in those areas already struggle to get enough nutrition. 

Rapidly warming waters are likewise reducing the nutritional content of giant sea kelp, which serves as a crucial food source in the open ocean.

Certain herbivores may be hit harder, particularly those needing higher-quality diets. Hind-gut fermenters – such as rodents, rabbits, koalas, horses, rhinoceroses, and elephants – rely on microbes in their intestines to extract nutrients from fibrous plant materials, so they need nutrient-rich forage. 

Smaller animals, with faster metabolisms, also depend on more nutrient-dense food and may struggle if plant quality falls.

Further research is needed

To grasp the role of nutrient dilution in population declines, more evidence is needed. This includes artificial experiments that raise CO₂ levels to mimic climate change, along with field studies that track changing plant chemistry and its impact on wild animal populations.

Over the long term, scientists aim to uncover how decreasing plant nutritional value might reshape food webs. Changes to plant species, traits, and interactions could alter relationships among predators, prey, and ecosystems at large. 

At a time when climate change is already straining the planet, nutrient dilution adds another subtle yet far-reaching challenge that may reshape life on Earth.

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