Plants can absorb more carbon dioxide than we thought

Plants will store more CO₂ in a very high-emissions world, according to a new study in Science Advances.

The study finds that “gross primary production” – the rate of energy captured by photosynthesis – could increase towards the end of the century with high emissions.

“Plants take up a substantial amount of carbon dioxide every year, thereby slowing down the detrimental effects of climate change, but the extent to which they will continue this CO₂ uptake into the future has been uncertain,” says lead author Dr Jürgen Knauer, from Western Sydney University’s Hawkesbury Institute for the Environment.

“What we found is that a well-established climate model that is used to feed into global climate assessments by the likes of the IPCC, (Intergovernmental Panel on Climate Change) predicts stronger and sustained carbon uptake until the end of the 21st century when extended to account for the impact of some critical physiological processes that govern how plants conduct photosynthesis.”

Previous research has suggested that plants may be able to absorb less CO₂ in extreme conditions brought on by climate change.  The researchers used more detailed ecological models to figure out if this was the case.

“We accounted for aspects like how efficiently carbon dioxide can move through the interior of the leaf, how plants adjust to changes in temperatures, and how plants most economically distribute nutrients in their canopy,” says Knauer.

“These are three really important plant response mechanisms that affect a plant’s ability to ‘fix’ carbon, yet they are commonly ignored in most global models.”

The researchers used the worst-case emissions scenario to do their modelling: Representative Concentration Pathway (RCP) 8.5. Developed by the IPCC, this scenario assumes that emissions will continue to rise steadily over the next century. It’s not intended to be the most likely emissions scenario.

The researchers also ran their model under the most ambitious emissions scenario (RCP 2.6), finding gross primary production increased much more slowly in the first half of the century and then declined. They did not check intermediate scenarios.

Co-author Professor Ben Smith, director of the Hawkesbury Institute, says that their research will help to inform future carbon cycle models.

But he cautions against considering this a solution to the climate crisis.

“Simply planting trees will not solve all our problems and can at best contribute over a transitional period as society weans itself off fossil fuels. Ultimately, we need to eliminate emissions from all sectors. Growing trees alone cannot offer humanity a get out of jail free card.”