Reverse expectation ... Perennial trees do not help with warming

The little Muhammad Western

A new study showed that mature forests absorb carbon dioxide much less than previously thought, which indicates the need to review the currently approved models that consider forests to be a reservoir to get rid of an important proportion of this greenhouse gas.

Plant nutrition
Carbon dioxide is sometimes described as "plant food", as it is the main ingredient in plant photosynthesis.

And with the increased concentration of this gas in the atmosphere steadily due to human emissions, scientists have found abundant evidence of increased photosynthesis in plants that use the extra carbon they get to grow faster.

However, scientists have long questioned whether perennial trees can actually benefit from additional photosynthesis for growth.

Current climate change models estimate that older or older trees must absorb about 12% of carbon dioxide from the atmosphere and store them so they do not return to the ecosystem and contribute to warming.

In the new scientific study published earlier this month in the journal Nature, a team of researchers from Western Sydney University, led by Professor Belinda Medellin, measured CO2 absorption rates for 90-year-old eucalyptus trees in a forested area near Sydney over a four-year period. Continuous years.

The researchers used hanging rings of tubes that were built over the forest to pump quantities of carbon dioxide into the forest below to raise levels about 38% above the normal level.

Watch the Western Sydney University channel video about the study's details and results

Where did the carbon go?
The results of the study showed that forests consisting of older trees absorb carbon dioxide much less than previously thought, nor were they able to isolate the carbon dioxide they absorbed to prevent it from returning back into the atmosphere.

As expected, the trees absorbed about 12% of the additional carbon gas they got but could not grow faster, which raised the question "Where did the carbon go?"

Usually plants and trees absorb carbon dioxide as part of photosynthesis, which stimulates growth. Instead, perennial eucalyptus seemed to simply circulate carbon dioxide through the soil before it was released back into the atmosphere.

To explain this process, Medellin says, "The trees convert the absorbed carbon into sugars, but they cannot use these sugars to grow more, because they cannot get additional nutrients from the soil."

Instead, trees get rid of these sugars in the soil for microbes and fungi to take food there.

Climate Models for Review
According to the team, the trees get rid of about half of the carbon dioxide they absorbed through the soil, where they are processed and then released back into the atmosphere through soil bacteria or small fungi. As for the second half of these quantities, the trees get rid of it directly in the atmosphere.

This means, according to Dr. Mingkai Jiang, lead author of the study, "Long-term exposure to increased levels of carbon dioxide can only increase carbon storage in ecosystems that contain young trees or fertile soil."

Researchers expect that these results will have global impacts. The models used to predict future climate change, and the effects of climate change on plants and ecosystems, currently assume that perennial forests continue to absorb carbon above their current levels and act as carbon dioxide basins.

But the new study suggests that these ponds may actually be weaker than expected or not found in perennial forests and where the soil is low in nutrients.