FOLIAGE RESPONSES OF SPRUCE TREES TO LONG-TERM LOW-GRADE SULFUR-DIOXIDE DEPOSITION

Foliage on spruce trees (Picea rubens Sarg.) growing on dry SO2 deposi tion zones (dry SO2 deposition ranging from 0.5 and 8.5 S kg ha(-1) ye ar(-1)) downwind from a SO2 emission source was analyzed to assess chr onic effects of long-term low-grade SO2 deposition on net photosynthes is, stomatal conductance, dark respiration, stomatal antechamber wax s tructures, elemental concentrations in and on foliage (bulk and surfic ial concentrations), and types of epiphytic fungi that reside in the p hylloplane. Elemental distributions on stomatal antechambers, on funga l colonies, and on smooth surfaces between stomates and fungus colonie s were determined with a scanning electronic microscope (SEM) by way o f X-ray scanning. It was found that net photosynthesis of newly develo ped spruce foliage (current-year, and 1-year-old) was not significantl y affected by the local SO2 deposition rates. Sulfur dioxide depositio n, however, may have contributed to the gradual decrease in net photos ynthesis with increasing needle age. Dark respiration rates were signi ficantly higher on foliage taken from high SO2 deposition zones. Stoma tal rod-web structures deteriorated to flakes with increasing needle a ge and increasing SO2 deposition. Further inspection of the needle sur faces revealed an increasing abundance of fungal colonies with increas ing needle age. Many fungal taxa were isolated and identified. It was found that black yeasts responded positively, and Xylohypha pinicola r esponded negatively to high rates of SO2 deposition. Surficial concent rations of elements such as P, S, K, Cl, Ca were about 10 times higher on fungal colonies than on smooth needle surfaces. Surficial Ca conte nts on 4 or 5-year-old needles decreased with increasing SO2 depositio n, but surficial S concentrations remained the same. In contrast, bulk foliar Ca and S concentrations increased with increasing SO2 depositi on.