CO2 uptake decreases

Photosynthesis of trees becomes less efficient above 30 degrees Celsius

Above temperatures of 30 degrees Celsius, the photosynthesis of trees becomes inefficient. As a study by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) shows, the water loss of trees increases above this temperature, while CO₂ uptake decreases.

The study, which was published in the specialist journal "New Phytologist", thus calls into question the conventional assumption that a reduction in photosynthesis at high temperatures is solely due to diffusion limitations of CO₂.

Limit in the biochemistry of trees?
As the researchers showed, trees reduce their uptake of CO₂ even when there is actually enough carbon dioxide in the air. The study indicates "that there is a limit in the biochemistry of trees above around 30 degrees Celsius," says study leader Marco Lehmann from WSL.

Inefficient photosynthesis over a longer period of time can severely impair the growth, development and adaptability of trees or plants and ultimately affect the entire forest ecosystem, the WSL reported on its website on Monday.

Different tree species examined
In their study, the Swiss scientists examined the tree species beech, spruce, sessile oak and small-leaved lime, which all reacted in the same way to temperatures above 30 degrees.

According to the WSL, this study was possible thanks to a new experimental facility. This allowed the researchers to expose the plants to different environmental conditions under controlled conditions and track how the plants behave by means of gas exchange and isotope measurements.