EFFECTS OF AMMONIA, AMMONIUM-SULFATE AND SULFUR-DIOXIDE ON THE FROST SENSITIVITY OF SCOTS PINE (PINUS-SYLVESTRIS L)

The deterioration of forest vitality has been at least partly attributed to air pollution. Especially NH3, originating from intensive livestock farming and locally deposited in high concentrations, may contribute to forest decline in The Netherlands. Therefore, the effect of NH3 and SO2 fumigations on cold stress and water stress of Pinus sylvestris were examined. P. sylvestris trees (3 yr old) were exposed to ambient air supplemented with several NH3 concentrations, with SO2 or a combination of NH3 and SO2. Tops of branches were then exposed to various subzero temperatures and the effect of air pollution on frost damage was examined. Neither ambient air, NH3 or SO2 significantly influenced from sensitivity at -4 or -7-degrees-C. Following freezing treatments of -10-degrees-C, the influence of NH3 and SO2 became apparent. The effect of the combination of these pollutants is synergistic. Exposure to NH3 alone followed by freezing temperatures lower than -10-degrees-C resulted in more severe frost damage in early autumn and spring than in the winter. It also increased the susceptibility of P. sylvestris to water stress. A greater loss of water was observed in NH3-fumigated needles following drought stress, suggesting increased cuticular transpiration. Bud burst and subsequent shoot growth was also strongly reduced by NH3 fumigations.