Plants Responding To More CO2 In Atmosphere By Photosynthesizing More — But Not Matching CO2 Increase

SciTechDaily reported that there’s some new and interesting research from Berkeley Lab and UC Berkeley that show plans are photosynthesizing more in response to more carbon dioxide in the atmosphere. Plants pull carbon dioxide from the atmosphere and convert it into food, which makes forests and other ecosystems some of our planet’s most critical carbon sinks.

However, our activities on the plant have contributed to the massive amounts of greenhouse gases such as carbon dioxide being released into the atmosphere. The article noted that this was a cause of debate among scientists for a while, and at the time, they couldn’t really prove whether or not plants were responding to the increase in carbon by photosynthesizing more. That has changed.

A team of researchers lets by Lawrence Berkeley National Laboratory and UC Berkeley used a new type of methodology that combines remote sensing, matching learning, and terrestrial biosphere models and found that plants are photosynthesizing more.

The researchers found that the amount the plants are photosynthesizing is up 12% higher than the global photosynthesis average from 1982 to 2020 — an almost 40 year period. During this time period, global carbon dioxide concentrations in the atmosphere grew to around 17% from 360 parts per million (ppm) to 420 ppm.

The article noted that the 12% increase in photosynthesis is equivalent to 14 petagrams of additional carbon removed from the atmosphere by plants every year.

Trevor Keenan, lead author of the study and a scientist at Berkeley Lab, pointed out that the large increase in photosynthesis is great but isn’t close to removing the amount of carbon dioxide that needs to be removed.

“This is a very large increase in photosynthesis, but it’s nowhere close to removing the amount of carbon dioxide we’re putting into the atmosphere. It’s not stopping climate change by any means, but it is helping us slow it down.”

The Problem With The Current Measuring Of Photosynthesis

The article dove into the history and challenges of how global photosynthesis is measured.

When plants are photosynthesizing, tiny pores on the surfaces of their leaves open up to take in carbon dioxide from the air. This is how they produce their food. By placing a leaf in a closed chamber and quantifying the dropping of carbon dioxide levels of the air inside, scientists were able to measure just how much plants were photosynthesizing. However, it’s much more difficult to measure how much carbon dioxide an entire forest takes up.

AmeriFlux, which is a network of measurement sites that is coordinated by the Department of Energy’s AmeriFlux Management Project at Berkeley Lab, has helped scientists all over the world build over 500 micrometeorological towers in forests to measure the exchange of carbon and other greenhouse gases in the atmosphere with the vegetation and the soil.

However, the downside is that the flux towers are costly and limited in their geographic coverage. So scientists have been relying on satellite images to see how much of the earth is green (covered in forests), which enables them to determine the global photosynthetic activity.

Although satellite images can show the extra green that accounts for the leaves that plants put out due to accelerated growth, they don’t account for each individual leaf’s increased efficiency to photosynthesize. Also noted was that efficiency does not increase at the same rate at which carbon dioxide is built up in the atmosphere.

A Solution To The Challenges

Keenan, who’s also an assistant professor at UC Berkeley’s Department of Environmental Science, Policy and Management, pointed out that this magnitude is highly important and if the increase in photosynthesis is small, then we may actually have the carbon sink that we expect. His team of teachers took a new approach to solve these challenges.

The team analyzed almost three decades of carbon sink estimates that were made by the Global Carbon Project and compared these with predictions from satellite images of the earth taken between 1982 and 2012. They also compared it with models using carbon exchange between atmosphere and land to make the carbon sink estimate.

This is where Keenan and his team came up with that 12% number.

“Our estimate of a 12% increase comes right in the middle of the other estimates. And in the process of generating our estimate, it allowed us to re-examine the other estimates and understand why they were overly large or small. That gave us confidence in our results.”

It’s unclear, Keenan pointed out, how long forests will continue to photosynthesize this much carbon at this rate. The study also highlights the importance of protecting these ecosystems that are trying to help slow down the rate of climate change.

“We don’t know what the future will hold as far as how plants will continue to respond to increasing carbon dioxide. We expect it will saturate at some point, but we don’t know when or to what degree. At that point, land sinks will have a much lower capacity to offset our emissions. And land sinks are currently the only nature-based solution that we have in our toolkit to combat climate change.”

You can read the full article in SciTechDaily here.