Forests may store less carbon dioxide than previously thought

Trees, like other plants, make their own food through the process of photosynthesis. They extract carbon dioxide from the air and convert, together with water, the gas into glucose under the influence of sunlight. that feeds solid cell expansion and cell division in the cambium of trees, the layer below the bark where growth occurs. Carbon dioxide from the atmosphere constitutes the carbon source for trees, and new woody cells are the carbon sink where carbon dioxide is stored.

Antoine Capon, a postdoctoral researcher and forest ecologist at the University of Utah in the US, says a common assumption is that both processes are linearly related. Cabon specializes in research into the impact of climate on trees and forests. ‘supposed to Bo . growthPowered by photosynthesis. The more carbon dioxide a tree absorbs, the stronger the growth, and therefore more carbon dioxide is stored in the biomass. However, our research shows that these two processes – photosynthesis and growth – do not show a strong association.

Capone and his team. On the one hand, the data from the so-called flow towers, the towers that rise above the foliage and measure the interaction between the atmosphere and the forest, and on the other hand, the growth rings that tell us more about the growth of trees. The research is limited to forests from temperate and boreal regions, because tropical trees often do not form clear growth rings and little data is available on them. Surprisingly, a comparison of these two types of data shows that photosynthesis and growth do not show a strong relationship.

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This can be explained by climatic conditions and forest structure, says Capone. ‘The accumulation Of the trees stop at temperatures below 5 ° C, while photosynthesis is still taking place. Another factor is the availability of water. During drought, cell growth and division slows down, and at some point the tree stops growing. Then we also see a disconnect between photosynthesis and cell activity in the cambium of trees. Moreover, the correlation is weaker in thickly leafy forests.

Human carbon dioxide emissions are increasing their levels in the atmosphere, causing global warming. This extra CO2 in the air also ensures additional photosynthesis. But our research shows that this does not translate in a straight line to stronger tree growth. How a changing climate affects forests depends on the region and climatic conditions. In boreal forests, increased temperature can lead to increased growth, while increased drought elsewhere has the opposite effect.

The findings have implications for climate models, as forests are the primary carbon sink. Forests account for up to a quarter of our emissions as biomass. Current models are based on the assumption that photosynthesis determines tree growth. Our results contradict this. More carbon dioxide actually means more photosynthesis, but that doesn’t linearly lead to stronger tree growth. So forests may store less carbon dioxide than we previously thought.

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