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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The effects of summer exposure to ozone on the frost hardiness after the vegetation period of Norway and Sitka spruce seedlings P. W. Lucas Biological Sciences, (Division of Institute of Environmental and of Biological Sciences), University Lancaster, Lancaster, LA1 4YQ. U.K. fected the frost hardening and deharden- Introduction ing of Norway spruce (Picea abies L. Karst) and Sitka spruce (P sitchensis No single cause has been identified to [Bong] Carr) such that their susceptibility explain the decline of coniferous trees in to frost damage was increased. some high-elevation forests in Europe and parts of the USA, but a consensus view among researchers is that the observed changes are associated with air pollutants. Materials and Methods Air pollutants are, however, only one of a variety of environmental stresses which and Ozone fumigafion growth measure- may affect the physiology of trees and ments which 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 randomly occurring, 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 d integrity is thought to be the major cause per wk at an average hourly concentration of of frost injury (Levitt, 1980), there are 140 μg·m- the remaining chambers received ; 3 good physiological reasons to believe that charcoal-filtered air and acted as controls. ozone could increase the sensitivity of plants 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- to were in the chambers to frost harden until lateral during the summer af- shoot elongation had ended and minimum air posure to ozone
the shoots but, compared to the temperatures had fallen below 10°C. The first Norway test was therefore not carried out until freezing shoots at this time, there was quite a the 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 of each tree were frozen in an unlit programmable ca 0.3°C d- compared to the Sitka which 1 freezing 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 of jected to separate freezing tests in the range -5 to -25°C, with cooling and warming rates of 5°C hardiness. The Norway shoots may, how- 1 h- 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 temperature the middle portion of each shoot was placed in which could be attained by the freezing a 20 ml polypropylene vial and 15 ml of deion- chamber was only -25°C. For this second ised water were added. The vial was capped, shaken and stored at 6°C. Solution conductivity freezing test and for the tests made at was measured after 24 h using a platinum elec- later dates, there were no significant trode. The samples were stored at 6°C for a fur- effects of ozone on the freezing sensitivity ther 5 d and the conductivity was again mea- of shoots from either species of spruce. sured. After this second reading, the shoots were stored at 6°C and after 14 d scored for Over the period 24 November-20 visual damage (0 no damage, 1 50% damaged, 3 = = age rate of the Norway spruce shoots and brown, assumed dead). The shoots + vials were then autoclaved and the total conductivity (C-) it is probable that they were hardy to of the solution determined. Based on the temperatures considerably in excess of assumption that the rate of leakage of electro- the minimum freezing temperature shown lytes from a detached shoot is controlled by dif- (Fig. 2). In contrast, the Sitka shoots had fusion, the conductivity of the solution at any only attained a further 3°C of hardiness time (C,) can be described by a first-order reac- tion equation: C G {1 e-’&dquo;). ). t = during this time. By logarithmic transformation of the above By mid-May, bud burst had occurred in equation and substitution of the measured all the trees and a freezer test at this time conductivity values, the rate of change in showed that shoots of both species had conductivity or normalised leakage rate (k) was calculated. A comparison of k values with dehardened to temperatures between -5 visible damage showed for both species of and -10°C (Fig. 3). spruce that shoots with k values >0.35% I h- would be killed. Discussion and Conclusions Results Exposure to ozone delayed the frost hard- ening of Norway spruce shoots during By the time of the first freeze test on 20 mid-autumn. Similar results for Norway October 1987 (Fig. 1the Norway spruce spruce have also been observed by other had hardened to a temperature of about researchers, both with ozone (Barnes and - 19°C, although there was a delay in Davison, 1988) with S0 and N0 in com- 2 2 hardening in those shoots that had been bination (Freer-Smith and Mansfield, exposed to ozone. For the Sitka spruce, 1987) and with acid mist (Cape et al., there was no effect of pollutant exposure 1988). The results of the present study, on the timing of frost hardiness attained by
therefore, appear to support the hypothe- sis that air pollutants may predispose Nor- way spruce trees to damage by frosts. For Sitka spruce, however, there were no effects of ozone on delayed frost hard- ening and the results differ from those reported previously by Lucas et al. (1988), in which spruce seedlings were exposed to a similar concentration of ozone using the In this case, fumigation system. same although there was no effect of the pollu- tant on the attainment of deep winter hard- iness, the sensitivity of detached shoots to autumn frosts was found to be increased. experiments, but other environmental two At present it is difficult to offer an explana- factors may be involved in modifying the tion for the different results between the plant’s response to the ozone.
Acknowledgments Freer-Smith P.H. & Mansfield TA. (1987) The combined effects of low temperature and S0 + N0 pollution on the new season’s 22 This work supported in part by the UK growth and water relations of Picea sitchensis. was of the Environment, the Commis- Department New Phytot. 1 O6, 225-237 sion of the European Communities, the NE Heath R.L. (1980) Initial events in injury to Forest Experiment Station of the USDA Forest plants by air pollutants. Annu. Rev. Plant Phy Service and the US Environmental Protection sioL 31, 395-401 Agency, as part of the National Acid Precipita- Levitt J. (1980) Responses of plants to environ- tion Assessment Program. mental stresses. In: Physiological Ecology Series. (2nd edn. Vol. 1) Chilling, Freezing and High Temperature Stresses. Academic Press, New York, pp. 254-262 References Lucas P.W., Cottam D.A. & Mansfield TA. (1987) A large-scale fumigation system for investigating interactions between air pollution Barnes J.D. & Davison A.W. (1988) The influ- and cold stress on plants. Environ. Pollut. 43, of ozone on the winter hardiness of Nor- ence 15-28 way spruce. New Phytol. 108, 159-166 Lucas P.W., Cottam D.A., Sheppard L.J. & Cape J.N., Sheppard L.J., Leith I.D., Murray Francis B.J. (1988) Growth responses and M.B., Deans J.D. & Fowler D. (1988) The delayed winter hardening in Sitka spruce fol- effects of acid mist on the frost hardiness of red lowing summer exposure to ozone. New Phy- spruce seedlings. Aspects Appl. Biol. 17, 141- tol. 108, 495-504 149