Use of carotenoid ratios, ethylene emissions and buffer capacities for the early diagnosis of forest decline.

Norway spruce trees were sampled at twelve sites in Western Europe; each site was known to have been exposed to different levels of atmospheric pollutants. Amongst a wide range of other tests, ratios of needle pigments and buffering capacity were measured in needle samples taken from each site and gas samples taken from similar twigs were subsequently analysed for hydrocarbons. Rates of ethylene emissions were low from needles in relatively unpolluted areas and higher at sites experiencing frequent ozone episodes, higher rainfall acidity or elevated levels of primary pollutants. A similar trend was observed for certain pigment ratios, and a strong correlation was found between ethylene emissions and the ratios of violaxanthin to antheraxanthin. The buffering capacities of 2-year-old needles did not differ in any consistent way between sites. In current-year needles, alkaline buffering was significantly reduced at polluted sites but no significant site-related trend towards acidic buffering was apparent. The relative value of each of the three tests as early diagnostic indicators of pollutant damage is discussed