Soil dressing with sulphur: does it reduce frost hardiness in spruce seedlings?

Abstract

This experiment was undertaken to quantify the effects of root absorbed SO 2− 4 on frost hardiness, an indicator of physiological perturbation. Experiments with acid mist suggest that the root mediated pathway for SO 2− 4 uptake exerts a relatively small detrimental effect on frost hardiness. Bare-root transplants of Sitka and red spruce seedlings were grown outdoors for one growing season, in compost top dressed with different fertilizer treatments, with or without SO 2− 4. Without SO 2− 4: Vitax Q 4, KNO 3 and NH 4H 2PO 4. With SO 2− 4: K 2SO 4, (KNO 3 + K 2SO 4) and (NH 4H 2PO 4 + K 2SO 4). 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 SO 2− 4 did not significantly enhance rates of electrolyte leakage from frozen shoots of either Sitka or red spruce, even at S dose rates exceeding (by a factor of at least 4), those likely to be supplied as acidic deposition. Reductions in frost hardiness were observed where SO 2− 4 was added, but these effects were not significant confirming that foliar uptake of S is necessary for the significant reductions in frost hardiness caused by acid mist.