Tuesday, December 5, 2023

Plants may absorb more CO2 amid climate change

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The world’s vegetation has a remarkable ability to absorb carbon dioxide (CO2) from the air and store it as biomass. In doing so, plants slow down climate change since the CO2 they take up does not contribute to global warming.
But what will happen under more advanced climate change? How will vegetation respond to projected changes in atmospheric CO2, temperatures and rainfall? Our study, published today in Science Advances, shows plants might take up more CO2 than previously thought.
We found climate modelling that best accounted for the processes that sustain plant life consistently predicted the strongest CO2 uptake. The most complex model predicted up to 20% more than the simplest version. Our findings highlight the resilience of plants, and the importance of planting trees and preserving existing vegetation to slow climate change. While this is good news, it doesn’t let us off the hook in the fight against climate change. The rapid increase in atmospheric CO2 means we must still cut emissions.

What happens to the CO2 plants take up?
Plants take up CO2 through photosynthesis. This process uses the Sun’s energy to convert or “fix” CO2 from the air into the sugars plants use for growth and metabolic activity. Plants release around half of that CO2 back to the atmosphere via respiration relatively quickly. The other half is used for growth and stays in the plant biomass for longer months to centuries.
That biomass will eventually die and decompose. Part of the carbon will be released again to the atmosphere, but other parts will enter the soil where it can stay for hundreds of years.
So, if plants take up more CO2, it’s likely more carbon will be stored in vegetation and soils. This “land sink” of carbon has indeed increased over the past few decades as the annual global carbon budget assessment has shown. What’s more, the increasing land carbon sink has largely been attributed to the beneficial effects of rising atmospheric CO2 on plant photosynthesis. This is important because that carbon stored in plants and soils slows the increase in atmospheric CO2 and therefore global warming.

A gap in current climate models
But how do we know how much carbon is taken up and stored on land? Even more challenging, how can we predict what happens in the future?
One attempt to answer these questions is to use so-called terrestrial biosphere models. These models encapsulate our understanding of how plants function and how they respond to changes in climate.
For example, we know from experiments that plants photosynthesise more under higher CO2 concentrations but less when they don’t have enough water. Models translate all this knowledge into mathematical equations and allow them to interact with each other. All this knowledge? Well, not really, and that was the motivation for our research. While today’s terrestrial biosphere models include a plethora of processes, they do not necessarily account for all mechanisms and processes that we know exist. There might not be enough data or information available to confidently represent a process across the entire globe, or it might just be difficult conceptually or technically to include it in models.

What did the study look at?
We included three of those neglected processes into the well-established Australian terrestrial biosphere model. We accounted for: how efficiently CO2 can move inside the leaf how plants adjust to changes in their surrounding temperature how they distribute nutrients most economically.

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