SO2 directly affects vegetation by uptake through parts of the plants that are above
the ground; the direct effects on leaves are mainly determined by air concentrations.
Depending on the amount of SO2 taken up per unit of time, various kind of
biochemical and physiological effects take place in the plant tissue; these include the
degradation of chlorophyll, reduced photosynthesis, raised respiration rates, and
changes in protein metabolism. The lower plants such as lichens and mosses, due to
their structure have a particular sensitivity to SO2.