Response to three seasons of elevated ozone in the progeny of healthy and unhealthy Norway spruce trees from a plantation with the 'top dying' syndrome

We tested a hypothesis that elevated ozone was an eliciting or contributing factor in outbreaks of the 'top dying' (or 'subtop dying') syndrome in Nor way spruce (Picea abies). Progeny were used from open-pollinated trees with in a stand with the 'top dying' syndrome. The mother trees were classified in relation to the expression of the 'top dying' syndrome, and progeny from the healthiest and least healthy thirds of the population were exposed to high and low concentrations of ozone for three seasons. Elevated ozone did not affect height growth of the trees. It did not measurably affect net pho tosynthesis, stomatal conductance or instantaneous water use efficiency. Ch lorophyll and carotenoid contents were also not significantly affected by o zone concentration. In the first year, instantaneous water use efficiency w as lower in the progeny of the unhealthy mother trees than in the healthy m other trees. Furthermore, the unhealthy mother trees tended to produce long er annual shoots and showed more winter damage at the end of the experiment . None of these parameters were related to ozone concentration in the atmos phere. These results do not support a hypothesis that elevated ozone is a s ignificant contributory factor or an eliciting factor in the development of the syndrome.