Pollen can become bee ‘junk food’ as CO₂ rises

Bees may soon need to supplement their diet with protein shakes of their own. Pollen normally provides their protein. But rising levels of carbon dioxide (CO2) in the atmosphere have sapped pollen of its protein. That’s the finding of a new study.

When a bee visits a flower, she may drink its nectar and collect its pollen. Nectar is like a sugar-shot of energy. Pollen, in contrast, offers long-term nutrition. That pollen gives bees their only natural source of protein.

Scientists compared recently collected flowers from Canada goldenrod (Solidago canadensis). Then they compared pollen in them to pollen in goldenrod preserved at the Smithsonian Institution’s National Museum of Natural History in Washington, D.C. Today's plants have less protein, they found. Protein levels in pollen from the older, preserved flowers was 18 percent. Today's goldenrod pollen has only about 12 percent protein. That's about one-third less than 172 years ago. 

Over that same time frame, CO2 levels have gone up by more than one-third. (Back more than 170 years ago, they were about 280 parts per million in air. Today they are about 398 ppm.) Fueling much of that rise in CO2 has been the growing use of fossil fuels (such as coal and oil).

To test whether CO2 changes had played a role in the falling protein levels, the researchers conducted tests. They grew goldenrod for two years at CO2 levels of up to 500 ppm. More CO2 in the air led to lower levels of protein in the flowers’ pollen. The researchers published their findings April 12 in Proceedings of the Royal Society B.

What does this mean for bees?

Joan Edwards is one of the study’s authors. She studies plants and their pollinators at Williams College in Williamstown, Mass. This drop in pollen protein could affect a bee’s diet and health, she notes. “It’s like you’re eating a starchier diet. What would that do to us?” she asks. The simple answer: It would be like eating things that taste good but offer less nutrition — junk food.    

Both wild and domesticated honeybees need to eat lots of protein. They use it to feed their young, called larvae. They also need it to keep their immune systems healthy, says Cédric Alaux. He’s a bee biologist at INRA, the French agricultural research agency in Avignon.

Canada goldenrod is an example of a plant that blooms late in the year. This lets honeybees store its pollen for use throughout the winter. The drop in pollen protein seen in the new study would be big enough to shorten bee lifespans, Alaux says.

Bee populations have been declining globally in recent years. A drop in their food quality might play a role, Edwards says. And that drop might affect crop pollination too. Notes Edwards, “The health of the bee population is not just for the flowers and the bees and biodiversity." She worries it also could play a role in “human health and well-being.”

Power Words

(for more about Power Words, click here)

atmosphere   The envelope of gases surrounding Earth or another planet.

biodiversity   (short for biological diversity) The number and variety of species found within a localized geographic region.

carbon dioxide (or CO2)   A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

concentration   (in chemistry) A measurement of how much of one substance has been dissolved into another.

diet    The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.

domestication    A process of producing a tame version of an animal from a wild one, which can take thousands of years. A domesticated animal is one that has been bred in captivity.

fossil fuel   Any fuel — such as coal, petroleum (crude oil) or natural gas —  that has developed in the Earth over millions of years from the decayed remains of bacteria, plants or animals.

immune system   The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

larva     (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult.

parts per million (billion or trillion)  Frequently abbreviated as ppm (or ppb or ppt), it is a measure of the number of units of some material that it mixed into another. The units should be the same (or equivalent) for both materials. The term is used to describing extremely small concentrations of one chemical dissolved in another. For example, a solution of 300 parts per billion of sodium in water would mean that there are 300 sodium atoms for every billion water molecules.

pollen    Powdery grains released by the male parts of flowers that can fertilize the female tissue in other flowers. Pollinating insects, such as bees, often pick up pollen that will later be eaten.

pollinator    Something that carries pollen, a plant’s male reproductive cells, to the female parts of a flower, allowing fertilization. Many pollinators are insects such as bees.

pollinate   To transport male reproductive cells — pollen — to female parts of a flower. This allows fertilization, the first step in plant reproduction.

proteins     Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins.Medicines frequently work by latching onto proteins.

starch    A soft white chemical made by all green plants. It’s a relatively long molecule made from linking together a lot of smaller, identical building blocks — all of them glucose, a simple sugar. Plants and animals use glucose as an energy source. Plants store that glucose, in the form of starch, as a reserve supply of energy. Animals that consume starch can break down the starch into glucose molecules to extract the useful energy.