SOIL DRESSING WITH SULFUR - DOES IT REDUCE FROST HARDINESS IN SPRUCE SEEDLINGS

This experiment was undertaken to quantify the effects of root absorbe d SO42- on frost hardiness, an indicator of physiological perturbation . Experiments with acid mist suggest that the root mediated pathway fo r SO42- uptake exerts a relatively small detrimental effect on frost h ardiness. Bare-root transplants of Sitka and red spruce seedlings were grown outdoors for one growing season, in compost top dressed with di fferent fertilizer treatments, with or without SO42-. Without SO42-: V itax Q(4), KNO3 and NH4H2PO4. With SO42-: K2SO4, (KNO3 + K2SO4) and (N H4H2PO4 + K2SO4). These treatments supplied upwards of the equivalent of 71 kg N ha(-1) and 98 kg S ha(-1). At the end of the growing season , frost hardiness was measured on detached shoots, frozen in a purpose -built freezing cabinet and assessed for damage, indicated by the rate of electrolyte leakage from the frozen tissue. Soil top dressing with SO42- did not significantly enhance rates of electrolyte leakage from frozen shoots of either Sitka or red spruce, even at S dose rates exc eeding (by a factor of at least 4), those likely to be supplied as aci dic deposition. Reductions in frost hardiness were observed where SO42 - was added, but these effects were not significant confirming that fo liar uptake of S is necessary for the significant reductions in frost hardiness caused by acid mist. (C) 1997 Elsevier Science B.V.