Limited compensation of ozone stress by potassium in Norway spruce

The effects of potassium fertilization and ozone stress were investigated in a clone of Picea abies (L.) Karst, by studies of the uptake of CO₂ by the crowns, the element content, on leaching of the youngest needles, and the longevity of the needles. All plants were exposed to 0·075 μl litre^-1 SO₂ from January to April 1986. The average ozone concentrations applied during the subsequent growing season (May-December) were 0, 0·027, 0·050 and 0·100 μl litre^-1. Half of the trees received liquid fertilizer applications from April to July 1986. CO₂ uptake by the crowns was significantly reduced in non-fertilized plants at ozone doses of 100-200 μl litre^-1 h, whereas similar reductions were recorded in fertilized plants only above an ozone dose of 300 μl litre^-1 h. Independent of the fertilization, however, the concentrations of calcium, magnesium and nitrogen in the needles increased in parallel with the ozone dose, whilst potassium, phosphorus and sulphur showed little response to ozone. In both nutrient regimes, the diffusive loss of elements from chloroform-washed needles was similar and tended to be reduced at the highest ozone concentration, when relating the leachate to the corresponding element content in the needles. Needles formed in the highest ozone treatment were significantly shed during the succeeding year, regardless of the nutrient supply. It appears that increased potassium supply has little compensating effect on ozone stress in spruce.