Plants are more productive on weekends thanks to cleaner air

Plants in Europe photosynthesise more at the weekend, probably because there is less pollution in the air.

Photosynthesis is the chemical reaction that plants use to capture energy from the sun and convert carbon dioxide and water into sugar.

With increasing air pollution from wildfires, dust and human activities, Liyin He at the Carnegie Institution for Science in California and her colleagues wanted to see what effect air quality has on photosynthesis.

The team analysed satellite measurements of how much light is emitted by the green pigment chlorophyll in the leaves of plants – which corresponds to how much photosynthesis is occurring – across Europe between 2018 and 2021.

By comparing this with satellite measurements of air pollution over the same period, the team found that photosynthesis rates increased when there were lower levels of aerosols, a type of pollution that includes dust as well as smoke from wildfires and human activity.

These aerosols can stop sunlight from reaching Earth’s surface, which can hamper plants’ photosynthesising capacity. On the other hand, when there is less aerosol pollution in the atmosphere, more sunshine can reach the leaves of plants, says He.

The team found that higher rates of photosynthesis occurred at weekends in 64 per cent of Europe.

“There’s less traffic and industrial activities on the weekend,” says He. “But during the weekdays, the air is dirtier, so we see a strong weekly cycle.”

Furthermore, the team found that aerosol pollution reduced significantly in 2020 compared with other years due to the covid-19 pandemic. As a result, plants were more productive all week long, not just at the weekend.

The findings suggest that decreasing aerosol levels, especially those from transport or industrial processes, could allow plants to capture and store more carbon.

In fact, He and her colleagues calculated that an additional 41 million tonnes of CO2 could be removed by plants from the atmosphere every year if aerosol pollution levels dropped back down to the levels seen at the height of the pandemic.

“Improving air quality is not only beneficial for people’s health, but also very good for ecosystem productivity,” says He.