Trees could hold less carbon

It stands to reason that if a tree is photosynthesizing, it is also growing. But it is not always like that. This is revealed by a work from the Columbia Climate School (United States). It was published in 'Science Advances'. He discovered that although they photosynthesize well into the year, growth stops in mid-summer. Trees could hold less carbon than is believed.

Much of the long-term carbon storage provided by forests depends on this. That trees convert the carbon they absorb through photosynthesis into new wood. It is believed that increasing levels of carbon dioxide (CO2) in the atmosphere will boost photosynthesis and stimulate tree growth. And they will store part of that carbon that contributes to long-term global warming in the wood.

CO2 distributed

But it wouldn't be like that. Some of the absorbed carbon can be used to produce foliage or in short-term metabolic processes, rather than being stored long-term. This reduces the amount of carbon stored in forests compared to previous expectations. This finding has climate implications.

During photosynthesis, plants absorb CO2 from the air. They use sunlight to convert CO2 and water into sugars. Oxygen is released into the atmosphere, while carbon remains in the plant. Part of that carbon is incorporated into the woody biomass of the trunk, branches and roots. The rest is distributed in the foliage and fruits. And it is temporarily stored as starch.

At the California sites, oaks grew from December to April. But growth slowed in mid-summer and ceased in August, even as photosynthesis continued. About 26 percent of those trees' annual carbon uptake occurred after growth stopped.

still photosynthesis

When water is scarce, trees lose the internal water pressure they need to grow. “As soon as hot, dry conditions occur, growth activity stops almost instantly. Photosynthesis appears to continue at a slightly slower rate," they emphasize. Trees could hold less carbon than thought. Of course, it's not good news. The dissociation between photosynthesis and growth is greater in years of greater local climate variability. This pattern is expected to become more common as the climate changes.