Báo cáo lâm nghiệp: "Changes of partitioning and increased root lengths of spruce and beech exposed to ambient pollution concentrations in southern England"

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Changes of partitioning and increased root lengths of spruce and beech exposed to ambient pollution concentrations in southern England P.H. Freer-Smith 2 1 Taylor 2 M.C. Dobson G. Division of Biology, University of Lancaster, Lancaster LA1I 4 YQ, and 2 Forestry Commission, Alice Holt Lodge Farnham, Surrey GUiO 4 LH, U.K and shoots may be altered such that the Introduction allocation of biomass to roots is restricted (U.K. TERG, 1988). Extrapolation of such results to the field, in particular, to large Much circumstantial evidence exists to trees is unwise, since the concentrations suggest that drought may act as an incit- used in such experiments are generally in ing factor, accelerating the decline of excess of those experienced presently in forest trees exposed to chronic doses of rural Britain, and the fumigations are often air pollution. For instance, many reports conducted over extremely short time pe- suggest that major increases in the de- riods on a limited number of small trees. In cline of spruce occurred after hot and dry addition, little research in Britain has in and Germany. Similarly, Ling summers focussed on drought and 0 which are , 3 Ashmore (1987) suggested that for beech, known to occur together during summer loss of green leaves, production of small months, particularly in southern England. leaves and altered patterns of shoot The Forestry Commission has recently growth were amongst the symptoms developed 3 rural sites, each with 16 open associated with the decline of this species. top chambers, to study the effects of ambient concentrations of pollution on tree Experimental work on trees in controlled growth and physiology for a period of up environments has shown that exposure to to 5 yr. The work reported here describes gaseous pollution may increase suscepti- data collected from the southern England bility to drought in at least 2 ways. Firstly, site at Headley, Hampshire, where during stomatal behaviour may be altered, caus- the 1988 growing season concentrations ing both decreases and increases in water of 0 reached 85 ppb on at least 5 occa- loss (Mansfield and Freer-Smith, 1984) 3 sions. and, secondly, partitioning between roots * * address: St. Marv’" rollege. q Hill, W:aldearave Road. Twickenham TW1 4SX. U.K. Present Pm.
During July 1988, trees of both species were Materials and Methods harvested and, in addition to measurements of dry weight, root lengths were also assessed, using an automated device. For beech, roots 1 Experiment were sampled in 10 cm sections to a depth of Transplants (2 + 1 ) of beech (Fagus sylvatica 50 cm. L.) were rooted into 1 m plastic tubes containing compost. Tubes were sunk into the ground in open top chambers sited at Headley, Hamp- shire (Willson et al., 1987). Eight chambers used, 4 which received ambient air filtered were Results and Discussion through charcoal and 4 which received unfil- tered air. Regular measurements of gas ex- change were made from May until September Fig. 1 illustrates the effects of filtering on 1988, using field portable instruments. the rates of stomatal conductance for beech and spruce. For both species, sto- Experiment 2 matal conductance was restricted for trees grown in unfiltered (polluted) air, com- Clonal material of Sitka spruce (Picea sitchen- sis (Bong) Carr), was also placed into the same pared with the values in filtered (clean) air. chambers during April 1988. Plants were rooted Differences between mean values were into compost. Measurements of gas exchange tested using t tests and showed that this (photosynthesis, transpiration and stomatal effect was significant on 3 occasions for conductance) were made using a laboratory leaves of beecfi. system (Taylor and Dobson, 1989).
Similar effects also observed for in southern England may significantly redu- were photosynthesis and transpiration, suggest- carbon flux to and water loss from shoots ce ing that ambient concentrations of pollution of these important species. The conse-
quences of this consistent decline in gas Acknowledgments exchange are shown in TableI and Fig. 2. As for fumigation studies on small trees We thank W.J. Davies and T.A. Mansfield for (U.K., TERG, 1988), exposure to ambient guidance, the D.O.E. for financial support, A. pollution resulted in reduced root biomass Willson, D.W.H. Durrant and other staff at the for beech (Table I). Significant effects on Forestry Commission and P. Hutchinson for technical assistance. root:shoot ratio were also detected for spruce, such that in the ambient, unfiltered treatment, root:shoot ratio was increased. The most interesting discovery was that reduced biomass of roots was accompa- References nied by increased root length in the unfil- tered treatment. Detailed analysis of SRL (root length/unit dry weight) showed that Ling K.A. & Ashmore M.R. (1987) In: Acid Rain and Trees. NC publication booklet no. 19. C for beech, trees grown in ambient air pro- Focus nature conservation on duced thinner roots (higher SRLs); this Mansfield T.A. & Freer-Smith P.H. (1984) The effect was more pronounced lower in the role of stomata in resistance mechanisms. In: soil profile, perhaps indicating a reduction Gaseous Air Pcdlutants and Plant Metabolism. in primary root growth, relative to the proli- (Koziol M.J. & Whatley F.R., eds.), Butter- feration of the fine root system. worths, London, pp. 131-146 The data suggest that trees grown in Taylor G. & Dobson M.C. (1989) Characteristics unfiltered air could be particularly suscep- of photosynthesis, stomatal responses and water relations of Fagus sylvatica: impact of air tible to drought-stress, since thinner roots quality at a site in southern Britain. New Phy- may be prone to loss or turgor and rapid tol. in press dehydration. In addition, resistance to U.K. Terrestrial Effects Review Group (1988) In: water flow in such a root system would be The Effects of A.!idic Deposition on the Terres- particularly high. Conversely, many thin trial Environme.nt in the United Kingdom. roots may enable the plant to exploit soil Department of Environment, London. pp. 30-31 moisture and nutrients more effectively Willson A., Durrant D.W.H. & Waddell D.A. during well-watered conditions. Further (1987) Experimental work on air pollution. work is in progress to esta- experimental Research information note 121.87.SSS, Fores- blish the effects of drought on these trees. try Commission.