Báo cáo lâm nghiệp: The effects of summer exposure to ozone on the frost hardiness after the vegetation period of Norway and Sitka spruce seedlings

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Báo cáo lâm nghiệp: "The effects of summer exposure to ozone on the frost hardiness after the vegetation period of Norway and Sitka spruce seedlings"The effects of summer exposure to ozone on the frosthardiness after the vegetation period of Norwayand Sitka spruce seedlingsP. W. Lucas Biological Sciences, (Division ofInstitute of Environmental and of Biological Sciences), UniversityLancaster, Lancaster, LA1 4YQ. U.K. fected the frost hardening and deharden-Introduction ing of Norway spruce (Picea abies L. Karst) and Sitka spruce (P sitchensisNo single cause has been identified to [Bong] Carr) such that their susceptibilityexplain the decline of coniferous trees in to frost damage was increased.some high-elevation forests in Europe andparts of the USA, but a consensus viewamong researchers is that the observedchanges are associated with air pollutants. Materials and MethodsAir pollutants are, however, only one of avariety of environmental stresses which and Ozone fumigafion growth measure-may affect the physiology of trees and mentswhich could predispose or incite damage. At the beginning of May 1987, 25 2 yr old seed-In those areas where forest declines are lings of each species were assigned randomlyoccurring, daily concentra- mean ozone to each of 4 large-scale fumigation chambers, often above 100 !g-nrr3. Expo-tions are described previously by Lucas et al. (1987).sure to elevated concentrations of ozone Fumigation of thee seedlings began on 1 June 1987 and continued until 11 September 1987.is known to damage cell membranes In two of the chambers, trees were exposed to(Heath, 1980). Since loss of membrane ozone for 7 h each day (08:00-15:00) for 5 dintegrity is thought to be the major cause per wk at an average hourly concentration ofof frost injury (Levitt, 1980), there are 140 μg·m- the remaining chambers received ; 3good physiological reasons to believe that charcoal-filtered air and acted as controls.ozone could increase the sensitivity ofplants to freezing injury. Frost hardening and freezing tests The objectives of the present study At the end of the fumigation, the trees remained investigate whether long-term ex- towere in the chambers to frost harden until lateral during the summer af- shoot elongation had ended and minimum airposure to ozone the shoots but, compared to thetemperatures had fallen below 10°C. The first Norway test was therefore not carried out untilfreezing shoots at this time, there was quite athe 20 October 1987. 12°C) in marked difference (approximately On each sampling occasion, current year’s the depth of hardiness attained.lateral shoots were detached from each of 5 Between 20 October and 24 November,trees of each species and from each chamber.Two shoots, approximately 4 cm in length, from the Norway shoots hardened at a rate ofeach tree were frozen in an unlit programmable ca 0.3°C d- compared to the Sitka which 1freezing cabinet as described by Lucas et al. hardened at a rate of ca 0.2°C d- and 1(1988). Separate batches of shoots were sub- had acquired at least a further 5-6°C ofjected to separate freezing tests in the range -5to -25°C, with cooling and warming rates of 5°C hardiness. The Norway shoots may, how-1h- and 10°C h-!, respectively. The preset tar- ever, have hardened to much lower tem-get temperature was held for 3 h. After freezing, peratures, as the minimum temperaturethe middle portion of each shoot was placed in which could be attained by the freezinga 20 ml polypropylene vial and 15 ml of deion- chamber was only -25°C. For this secondised water were added. The vial was capped,shaken and stored at 6°C. Solution conductivity freezing test and for the tests made atwas mea ...