DETOXIFICATION OF SO2 IN CONIFERS DIFFERING IN SO2-TOLERANCE - A COMPARISON OF PICEA-ABIES, PICEA PUNGENS AND PINUS-SYLVESTRIS

Contents of organic sulfur, sulfate and the inorganic cations K+, Ca2, Mg2+, Mn2+ and Na+ were compared in needles of three conifer species differing in tolerance to chronic SO2 immissions. Sulfate and organic sulfur compounds were also measured in bark and wood. Field material was collected from Norway Spruce (Picea abies (L.) Karst.), Colorado S pruce (Picea pungens Engelm.) and Scots Pine (Pinus sylvestris L.) at sites where the SO2 concentration in air was high, and at another site where it was low. In general, sulfate contents were higher but cation contents lower at the sites where SO2 concentrations were high than w here they were low. Up to 114 mmol . (kg DW)(-1) sulfate was measured in four-year-old needles of Norway Spruce from the Erzgebirge (annual mean of SO2 in air 32 nl . l(-1)). Sulfate accumulation in this SO2-se nsitive conifer increased with SO2 concentration in ambient air and wi th needle age, indicating that the main part of the sulfate resulted f rom the oxidative detoxification of SO2. Loss of inorganic cations fro m ageing needles was reduced, or cation levels even increased, with in creasing needle age, while sulfate accumulated. Apparently, cations se rved as counter-ions for sulfate, which is sequestered in the vacuoles . Individual trees differed in regard to the nature of cations which a ccumulated with sulfate. Calcium, potassium and magnesium were the dom inating cations. Sodium levels were very low. Needles of the SO2-toler ant conifers Colorado Spruce and Scots Pine growing next to Norway Spr uce in the Erzgebirge did not accumulate, or accumulated less, sulfate with increasing needle age as compared to needles of Norway Spruce. H owever, somewhat more sulfate was found in the bark of the SO2-toleran t species than in the bark of Norway Spruce. Scots Pine contained dist inctly more sulfate in the wood than the other conifers. Since accumul ation of organic sulfur compounds could not be Introduction observed w ith increasing needle age, or in bark and wood, reduction does not app ear to play a major role in the detoxification of SO2 by the investiga ted species. Physiological mechanisms permitting Colorado Spruce and S cots Pine to avoid the sulfate accumulation in the needles and the acc ompanying sequestration of cations that are observed in neighbouring N orway Spruce are discussed on the basis of the obtained data.