Ozone-sensitivity of Scots pine and Norway spruce from northern and local origin to long-term open-field fumigation in central Finland

Long-term experiments are needed to study the effects of realistically low ozone concentrations. In our three-season-long experiment, seedlings of Scots pine and Norway spruce were exposed to slightly elevated levels of ozone in an open-field system in central Finland. Two provenances (one local and one from northern Finland) were used. The responses included increased needle chlorosis and changes in chlorophyll a and b, fatty acid ratios, secondary metabolites and ultrastructure. However, responses were rather mild and often had a slightly different pattern in different provenances, species and year needle classes. The fact that the ozone-induced effects were rare in the present study suggests that (i) Scots pine and Norway spruce are not very sensitive to slightly elevated levels of ozone or (ii) the observed nitrogen deficiency masked any ozone-induced effects. However, a differential behaviour of the seedlings from the two provenances was observed. It is concluded that the northern provenance specimens might be more ozone sensitive when transplanted to a more southern location with a warmer climate than those of the local provenance.