Increased Carbon Dioxide Causes European Forests to Increase Water-Use Efficiency

As the amount of carbon dioxide increases in our planet's atmosphere, it's important to find out what effect this will have on our world's trees. Now, scientists have found that increased CO2 actually increases the water-use efficiency of European broadleaf and coniferous trees.

During photosynthesis, trees take up carbon dioxide (CO2) from the air. In return, they lose water vapor (H2O) through tiny holes in their leaves, called stomata. This gas exchange is regulated through the opening widths of their stomata; for example, wider apertures allow the uptake of higher numbers of CO2 molecules, but promote water vapor loss.

"Assuming the trees demand for CO2 does not change, they can reduce the aperture of the stomates of their leaves and needles under increasing atmospheric CO2 concentrations," said Gerhard Helle, one of the researchers, in a news release. "This should lower the rates of transpiration and minimize the tree's water loss."

After examining the trees of European forests, the researchers found that there has been an increase in water-use efficiency since the beginning of the 20^th century by 14 percent and 22 percent. This can likely be attributed to a lengthened growing season, increase transpiration due to a warmer environment and an enhanced leaf area.

The findings are important for better estimates of the impact of forests on climate, improved model scenarios for future climate development and more reliable assessment of the global water cycle.

The findings are published in the journal Nature Climate Change.

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