So Far, Plants Are Keeping a Lid on Our Greenhouse Gases

A forest in Bavaria, Germany. (William Dotinga/CNS)

(CN) – As the planet warms, plants are keeping the pace to process carbon dioxide and slow the effects of human-caused climate change, according to research published Thursday in Trends in Plant Science.

Photosynthesis occurs when plants capture energy from the sun and use it to synthesize carbohydrates from CO2 and water and release them back into the atmosphere as oxygen. Since the beginning of the industrial era, plant synthesis has increased in nearly constant proportion to the rise in atmospheric CO2. 

“We can say that plants are working hard – the response is at the highest end of the expected range,” Lucas Cernusak, lead researcher and terrestrial ecologist at James Cook University in Cairns, Australia, said in a statement.

“We expected the two would correlate, since CO2 stimulates photosynthesis, but given the complexity of plant and environmental interactions we were impressed by how closely they have kept pace,” Cernusak said.

Cernusak worked with colleagues from CSIRO Oceans and Atmosphere in Canberra and the Université de Lorraine in France to measure the strength of the terrestrial biosphere’s response to increasing CO2. They focused on photosynthesis by examining terrestrial gross primary productivity which is a measure of global photosynthesis.

The researchers used a combination of existing analyses and new modeling, alongside laboratory studies, to examine how increased CO2 affects photosynthesis, from individual leaves up to a global scale.

“We know that terrestrial plants are currently absorbing more CO2 than is released into the atmosphere through the combination of fire, decomposition, plant respiration, and human-related emissions,” Cernusak said.

“This is commonly known as the land carbon sink, and we know it’s currently slowing the rate at which atmospheric CO2 is increasing. What we don’t know is how strong that response is, and how long we can count on it,” he said.

The increasing frequency of dramatic weather events, like heat waves, droughts and intense storms, has the potential to stress terrestrial vegetation and in turn slow photosynthesis.

“It’s also important to remember that global change will manifest differently in different regions,” Cernusak said.

“Our observations and modeling analyses suggest that in high-latitude ecosystems it’s global warming that is driving the increase in leaf area and growing-season length. That’s quite different from the tropics, where our study indicates that CO2 fertilization is driving the growth in photosynthesis, while climbing temperatures can create significant stress for some plant species.”

Cernusak and his colleagues say their modeling is an important step toward assessing how the earth’s plants will respond to climate change within different geographic regions and ecosystems and ultimately over the long haul. Thus far the planet’s plants have stepped up their production to keep human impacts in check, but further study and time will tell if they can give even more or if they will finally reach capacity.

Meanwhile, a study published Wednesday underscored we may not be able to count on forests to scrub our emissions from the atmosphere forever. Scientists from Cambridge University found that while plants and forests are flourishing from the infusion of carbon dioxide and warmer temperatures, they’re living fast and dying young – and they amount of carbon dioxide they can take up is diminishing as a result.

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