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Marcus Schaub

Forschungsanstalt WSL

Swiss Federal Research Institute WSL
Ecophysiology
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CH - 8903 Birmensdorf

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Article

Author(s): Marcus Schaub
Editorial office: WSL, Switzerland
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Ozone reduces the growth of poplar

Cheerless expectations for poplar plantations. In particular, the poplar responds with reduced growth rate to elevated ambient ozone concentrations which scientists from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) have been able to demonstrate.

Ozonsymptome an Pappelblatt
Fig. 1 - Advanced ozone symptoms on a poplar leaf.
Photo: Marcus Schaub (WSL)
 
Ozonsymptome an Eschenblatt
Fig. 2 - Also European ash (Fraxinus excelsior) develops visible, ozone-induced symptoms but the scientists could not find any reductions in growth.
Photo: Marcus Schaub (WSL)

The high ambient ozone concentrations rising every summer season not only harm human health and agricultural plantations, but also the growth of trees. The leaves "suck" air through the stomata and thus also take up ozone. Ozone affects the tree negatively and may reduce the growth rate. This can be shown by research done by scientists from the WSL who measured the thickness of tree rings and the carbon isotopes contained within.

The analysis of the isotopes, which was conducted at the Paul Scherrer Insitute, allowed conclusions about the effects of the ozone dose taken up by the leaves. The scientists compared the amount of isotopes to the thickness of the tree rings and were able to demonstrate that higher ozone concentrations lead to thinner tree rings. This is particularly true for fast growing trees species such as poplar. Other tree species, such as the ash, suffer from visible ozone-induced injury; however, based on the tree ring analysis, a growth reduction could not be found for ash.

As with people, the ozone concentration for trees per se is not crucial. The tree response to tropospheric ozone depends on the species, age, microclimatic conditions of the environment and over-all health. The team found that high ozone concentrations occurring early in summer during the growing season are particular harmful to the trees.

How much ozone is "allowed"?

A WSL-group, in collaboration with an international team, is currently investigating the ozone risk assessment for the forest as entire ecosystems. In order to protect the forests in Europe from adverse ozone effects, scientists are investigating a new ozone standard which takes the various factors influencing the tree response to ozone into account. The model calculates the ozone uptake for varying elevation above sea level, age classes depending on soil water availability, temperature, and many other factors.

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