The influence of elevated ozone on freezing tolerance of red spruce seedlings

Abstract

summaryLaboratory cold‐tolerance assessments were conducted over two seasons on red spruce (Picea rubens Sarg.) seedlings fumigated with various concentrations of ozone (O3) for one or two growing seasons in three independent experiments at three locations. Ozone fumigations were performed at either Boyce Thompson Institute in Ithaca, NY (BTI), the University of Maine in Orono, ME (UMO), or the US Forest Service Research Laboratory in Delaware, OH (USFS). Acid mist treatments of either pH 3.0 or 4.2 were applied in combination with O2 treatments at USFS, Seedlings fumigated with moderate or high concentrations of O3 were never significantly less cold tolerant than seedlings exposed to charcoal‐filtered (CF) air or low O3 concentrations. In fact, there was a tendency for seedlings fumigated with low concentrations of O3 or CF air to be the least cold tolerant. USFS‐fumigated seedlings receiving the lowest O3 concentration (50/0 nl 1−1, day/night concentration) were least cold tolerant on six of the seven sampling dates and significantly less cold tolerant in October and January. In addition, UMO‐fumigated seedlings receiving CF‐air were significantly less cold tolerant in January than those receiving either ambient air (no chamber or non‐filtered treatments) or elevated O3. Acid mist treatments had little influence on the cold tolerance of red spruce seedlings in autumn and early winter, but in January 1990 seedlings exposed to pH 3.0 acid mist were approximately 6 °C less cold tolerant than those receiving pH 4.2. Following the 1988‐89 winter, freezing injury was evident on all seedlings fumigated at BTI, but differences between 3 x ambient O3 and CF treatments were not significant.