Báo cáo lâm nghiệp: "The influence of acid mist upon transpiration, shoot water potential and pressure—volume curves of red spruce seedlings"

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The influence of acid mist upon transpiration, shoot water potential and pressure—volume curves of red spruce seedlings D. Fowler D. Eamus I. Leith Penicuik, EH 26 OOB, Scotland, U.K. Bush Estate, Institute of Terrestrial Ecology, 16-20°C. On 16/7/87 100 seedlings were Introduction inside each of 8 open top chambers placed (OTCs) at a site in Scotland, U.K. (55°50’N; Widespread forest decline has been docu- 2°13’W; 200 m altitude). Four different pH treat- mented in Europe and NE-U.S.A. (John- ments (pH 2.5, 3.0, 4.0 and 5.0) with simulated son, 1987; Woodman, 1987). This decline acid mist were supplied using dilutions of an equimolar solution of (NH and HN0 Q SO Z ) 4 - 3 increases with increasing altitude (Mc- Each chamber received twice weekly sprays Laughlin, 1985). One hypothesis to ex- with an equivalent of 2 mm precipitation per plain the decline and its altitude depen- spray. Spraying commenced on 24/7/87 and dence is that excessive proton input has a continued until 20112187. deleterious effect upon tree growth. Acid The following measurements were made: 1) input to the foliage and soil via wet and shoot water potential was determined at 09:00 dry deposition may be a major factor in h on 23/10/87 using a portable Scholander causing decline directly or indirectly by pressure bomb (Hellkvist et al., 1974). Eight replicate branches from pH ?-.5, 3.0, 4.0 and 5.0 predisposing the tree to additional biotic treated trees were measured. 2) Day and night and/or abiotic stress factors. transpiration rates were determined on 16/11/87 The maintenance of a favorable water for 10 entire seedlings, of pH 2.5 and pH 5.0 . status is a priority for continued growth treatments and 10 attached shoots enclosed in a cuvette. 3) Eight replicate shoots (rehydrated and survival, and many of the symptoms overnight as attached branches) from pH 2.5, associated with forest decline (crown thin- 3.0 and 5.0 treated seedlings were subjected to ning, root necroses) may be expected to pressure-volume analysis (Kim and Lee-Sta- influence plant water status. This paper delmann, 1984; Stadelmann, 1984). presents some of the results of a detailed study of the influence of acid mist on the water relations of red spruce seedlings. Results Materials and Methods Fig. 1 shows that branch water potential (’Pw) decreased from !.07 to -1.2 MPa as germinated and grown Red spruce seeds were treatment pH decreased from 5.0 to ?-.5. for 16 mo in a greenhouse maintained at
Day and night transpiration rates were 1.19 ± 0.06 mmol (day) and .tree- 1 s- ’ 0.54 ± 0.06 mmol (night) for .tree- 1 s- ’ whole trees treated with pH 2.5 mist, and 1.5 ± 0.14 mmol (day) and .tree- 1 s- ’ 0.68 ± 0.09 mmol (night) for pH .tree- 1 s- ’ 5.0 treated trees. Night:day ratio was 0.45 for both. The slightly greater values for pH 5.0 treated trees per tree was due to the slightly larger pH 5.0 trees. However, day and night transpiration rates for branches, expressed on a unit area basis, did treatment pH decreased. Solute potential not differ significantly (pH 2.5: 0.23 ± 0.04 mmol-m- (day), 0.099 ± 0.006 l 7 -s 2 (’ at zero turgor decreased with in- ’11’) 1 1 -s- 2 mmol-m- (night); pH 5.0: 0.22 ± 0.03 creasing treatment pH. 1 -s- 2 mmol-m- (day), 0.015 mmol!m-2!s-! Fig. 2 shows changes in e with turgor v (night)). (top) and RWC (bottom) for pH 2.5, 3.0 TableI is a summary of the data derived and pH 5.0 treated branches. -, increased linearly with turgor and increased curvili- from pressure-volume curves. Maximum turgor decreased from 2.35 to 1.3 MPa as nearly with RWC. pH 5.0 treated trees treatment pH decreased. The relative maintained the largest E at all turgors, pH y 2.5 treated trees maintained the smallest, water content (RINC) associated with zero turgor ( Yp=0) and the maximum bulk volu- with pH 3.0 intermediate between the two. For all RWCs greater than 90%, this trend metric elastic modulus ( decreased as ) Ev was observed, whilst at RWCs less than 90% 3 crossover points in the data oc- curred. Discussion and Conclusion The developms!nt of water stress is char- acterized by a decline in ’I In this study, w’ ’ as treatment pH decreased, branch *!, mild but significant decreased, revealing a water stress. Water stress occurs when the rate of water loss exceeds the rate of uptake. It was clear that the rates of day and night transpiration did not differ be- tween treatments. From needle drying curves (data not shown), cuticular resis- tance did not differ between treatments. This result is in contradiction to those of several investigators who noted a signifi- cant effect of acid rain/mist upon cuticle structure and/or resistance. The lack of
significant reduction in solute apparent effect in the present study may tion. A potential associated with zero turgor be due to an efficient repair mechanism or (Table I) was also observed as treatment because changes in structure can occur pH increased, further reflecting a de- without concomitant changes in cuticular in solute accumulation with resistance. It is suggested that uptake crease decreased pH of the treatment mist.- Tur- and/or supply of water may be impaired in gor ( was maintained to lower RI!VCs at the roots or acid-treated seedlings. Pres- p) W pH 2.5 than pH 3.0 treated branches. This sure-volume analysis revealed significant can result from either increased solute effects of the acid mist. Maximum turgor accumulation or reduced -,. The former (’Fp, max) decreased with decreasing did not occur; the latter did (Table I). A treatment pH. This decreased t maxp, y reduction in E indicates a more elastic cell reflects a reduction in solute accumula- y
Effects of Atmospheric Pollutants on Forests, wall, possibly the result of the acidification VVetlands and Ac Ecosystems, (Hutch- ricultural f of the apoplast leading to proton-induced inson T.C. & Meema K.M., eds.), NATO ASI cell wall loosening (Davies, 1973). Series, Springer-’Verlag, Berlin, pp. 83-99 Kim J.M. & Lee-3tadelmann O.Y. (1984) Water relations and cell wall elastic quantities in Phaseolus vulgaris leaves. J. Exp. Bot. 35, 841 - References 858 S.B. (1985) Effects of air pollution McLaughlin Davies P.J. (1973) Current theories on the forests. A criiical review. J. Air Pollut. Con- on mode of action of auxin. Bot. Rev. 39, 139-171 trol Assoc. 35, 5!; 2-532 Hellkvist J., Richards G.P. & Jarvis P.G. (1974) Stadelmann E.J. (1984) The derivation of the Vertical gradients of water potential and tissue cell wall elasticity function from the cell turgor water relations in Sitka spruce trees measured potential J. Exp. Bot. 35, 859-868 with the pressure chamber. J. Appl. Ecol. 11, 637-667 Woodman J.N. (1987) Pollution induced injury Johnson A.H. (1987) Deterioration of red spruce in North American forests: facts and suspicions. in the northern Appalachian mountain. In: Tree Physiol. 3, H 5