Báo cáo khoa học: "The behavior of oaks in response to natural and induced exposure to the surfactant ABS"

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Original article The behavior of oaks in response to natural and induced exposure to the surfactant ABS S Moricca E Paoletti C 2 Comparini Istituto 1 di Patologia e Zoologia Forestale e Agraria, Piazzale delle Cascine, 28, 50144 Florence; 2 Centre di Studio per la Patologia delle Specie Legnose Montane, CNR, Piazzale delle Cascine 28, 50144 Florence, Italy Summary — Quercus pubescens, Q frainetto, Q ilex and Q robur were sprayed with ABS (sodium dodecyl benzenesulfonate, a surfactant often found in marine aerosols) over 2 growing seasons to test the effect of the surfactant on the leaf wax structure. Though all species were affected, they dif- fered in their tolerance to ABS. The effect of ABS was also tested on the pollen quality of Q ilex. Pol- len from declining and apparently healthy individuals was germinated in cultures with different con- centrations of ABS. A negative effect on pollen germination and pollen tube length was noted. The reduction in pollen viability could affect the genetic resources of holm oak populations in the future. ABS / oak spp / pollen / wax structure Résumé — Réaction des chênes à l’exposition naturelle et simulée à l’ABS. Des arbres appar- tenant à Quercus pubescens, Q frainetto, Q ilex et Q robur ont été aspergés d’ABS (dodecylbenzè- nesulfonate de sodium, détergent souvent trouvé dans les aérosols marins) pendant 2 saisons de végétation, afin de tester l’effet du détergent sur les structures des cires foliaires. Alors que toutes les espèces étaient atteintes, des différences spécifiques ont été observées. L’effet de l’ABS sur la qualité du pollen de Q ilex a également été étudié. Le pollen issu d’arbres dépérissants et apparem- ment sains a été germé dans des cultures ayant des concentrations variables d’ABS. L’ABS exerce un effet négatif sur la germination du grain de pollen et le développement du tube pollinique. La ré- duction de la viabilité pollinique peut affecter les ressources génétiques du chêne vert dans le futur. ABS / chêne / pollen / cires foliaires INTRODUCTION of forest trees. on the genetic resources The oak forest ecosystem in Europe has recently begun to show signs of ’oak de- That the effect of air pollution on forest cline’ (Donaubauer, 1987), the most nota- trees varies both among and within spe- ble symptoms of which are leaf yellowing cies has been well established (Karnosky and curling, leaf stunting, precocious leaf et al, 1989), but there are still gaps in our and twig shedding, failure of the buds to knowledge about specific pollution effects
break, changes in the branching habit and in cultures of modified Brewbaker and sayed Kwack (1963) solution containing 200 g/l of su- abnormally intense flowering (Gellini, crose and 0, 1, 3, 5 or 7 mg/l of ABS. Each as- 1989). Along the Tuscan coast (where a say was replicated 3 times. The percentages of large part of the vegetation consists of germination was arcsin-transformed. All data oak), several symptoms of decline have were subjected to analysis of variance and to been attributed to wind-borne surfactants Tukey’s multiple range test (P =0.05). from the sea (Gellini et al, 1983, 1985). The present study seeks to assess the ef- fect of natural and artificial exposure to RESULTS ABS on the leaf waxes of 4 oak species and on the pollen quality of Quercus ilex. ABS the leaf of all spe- damaged waxes cies, though to different degrees. Damage included: disaggregation and fusion of the MATERIALS AND METHODS epicuticular and epistomatic wax, deactiva- tion of the stomata (through occlusion or The leaf waxes of 5-year-old seedlings of Quer- damage to the stomatal aperture as it was pubescens Willd, Q frainetto Ten, Q ilex L cus plugged by migrating fused wax or through and Q robur L were sprayed with ABS (sodium impaired function of the guard cells), le- dodecyl benzenesulfonate) and examined over 2 growing seasons (1990-1991). Ten seedlings sions and cracks in the cuticle, trichome per species (5 for the spray treatment and 5 abscission and destruction, and the col- controls) were maintained in a plastic chamber lapse of the secreting heads of glandular where, during each growing season, they were hairs (fig 1A-D). Damage decreased in the treated twice weekly for 10 weeks with 50 mg/l following order: Q pubescens, Q frainetto, ABS in a fog-type spray. This concentration cor- Q ilex and Q robur. The same trees were responds realistically to the mean found in rain- fall on the Tuscan coast (Bussotti et al, 1983). sprayed again in 1991: initial data revealed Prior to treatment each year, the leaves were structural degradation of the leaf waxes marked and, after each series of treatments, 2 similar to that of the year before, but the leaves per tree were collected and air dried, as relative tolerance among the species was described by Karhu and Huttunen (1986). From unchanged. the middle of each leaf, 2 disks of about 50 mm 2 each were removed, 1 for upper surface and 1 In the culture ABS, pollen containing no for lower surface examination. Samples were lower in germination damaged trees was sputtered with gold palladium film and examined than in the healthy-looking tree, and in by scanning electron microscopy (SEM) at 20 damaged trees it was lower on the wind- kV. ward side than on the leeward side (table Q ilex, the species selected for pollen analy- sis, is common along the Tuscan coast and in I). However, the germinative capacity in hilly areas further inland and for several years the healthy-looking individuals was less has exhibited abnormally intense flowering (Gel- than that reported for truly healthy Q ilex lini and Paoletti, 1990). Pollen for our study was that had never been exposed to marine collected in the San Rossore Park from 1 aerosol (54%) (Bellani et al, 1988). In the healthy-looking individual that was sheltered culture without ABS, pollen tubes were from the sea wind by other vegetation and from 3 directly exposed and declining individuals. On considerably shorter in damaged trees these latter trees, pollen was taken both from than in the ’healthy’ individual tested, but the windward and the leeward sides for compar- there was no difference in tube length be- ative analysis. Pollen viability was determined tween the windward and leeward sides of by fluorescein diacetate (Heslop-Harrison et al, exposed trees. The addition of ABS to the 1984). Each test was replicated 5 times. To de- culture reduced germination in all trees. termine germination, pollen grains were as-
artificial. Moreover, in the ABS- The extent of reduction increased with in- natural or creasing doses, until 0% germination was containing cultures, damaged trees exhib- reached at 7 mg/l for the ’healthy’ tree and ited a lower germination capacity than 5 mg/l for the damaged trees. Increasing healthy trees. Surfactant-induced reduc- ABS concentrations also reduced pollen tion of the number and length of pollen tube length in the ’healthy’ tree, but not tubes could diminish seed production and significantly in declining trees. quality by weakening microgametophytic competition for ovules, or it could increase the tolerance of succeeding generations DISCUSSION of trees by selecting for pollen grains that surfactant-tolerant. The alterations in are the leaf waxes and in the pollen noted in The results confirm that wet depositions this study suggest that current surfactant of a substance such as ABS are harmful levels in nature (Bussotti et al, 1983) give to oaks. The morphological and physio- cause for serious concern. Pollution ex- logical alterations to the leaf waxes have erts selective pressures in favor of more biological consequences, increasing the tolerant species, but thereby reduces ge- cuticular transpiration rate and leaving the netic diversity, which is crucial if species tree more vulnerable to parasites (Cape, 1983). Pollen quality is confirmed as a are to adapt to changing environmental sensitive indicator of air pollution, whether conditions.
Gellini R, Paoletti E (1990) Deposizioni acide e REFERENCES loro effetti sulla vegetazione. Atti seminario salvaguardia e gestione ambientale, Firenze Nov-Dic 1989-Jan 1990, CSSGNB, 63-69 Bellani LM, Paoletti E, Cenni E (1988) Air pollu- Gellini R, Pantani F, Grossoni P, Bussotti F, Bar- tion effects on pollen germination of forest bolani E, Rinallo C (1983) Survey on deterio- species. In: Sexual Reproduction in Higher ration of the coastal vegetation in the park of Plants (Cresti M, Gori P, Pacini E, eds), San Rossore (central Italy). Eur J For Pathol Springer-Verlag, Berlin, 265-270 13, 296-304 Brewbaker JL, Kwack BH (1963) The essential Gellini R, Pantani F, Grossoni P, Bussotti F, Bar- role of calcium ion in pollen germination and bolani E, Rinallo C (1985) Further investiga- pollen tube growth. Am J Bot 50, 859-865 tions on the causes of disorder of the coastal Bussotti F, Rinallo C, Grossoni P, Gellini R, Pan- vegetation in the park of San Rossore (cen- tani F, Del Panta S (1983) Degrado della tral Italy). Eur J For Pathol 15, 145-157 vegetazione costiera nella tenuta di S Ros- Heslop-Harrison J, Heslop-Harrison Y, Shivanna sore. Prov Pisana 4, 46-50 KR (1984) The evaluation of pollen quality, and a further appraisal of the fluorochromatic Cape JN (1983) Contact angles of water drop- (FCR) test procedure. Theor Appl Genet 67, lets on needles of Scots pine (Pinus sylves- 367-375 tris) growing in the polluted atmospheres. Karhu M, Huttunen S (1986) Erosion effects of New Phytol 93, 293-299 air pollution on needle surface. Water Air Soil Donaubauer E (1987) Auftreten von Krankheiten Pollut 31, 417-423 und Schädlingen der Eiche und ihr Bezug Karnosky DF, Berrang PC, Scholz F, Bennet JP Eichensterben. Osterreichische Forst- zum (1989) Variation in and natural selection for zeitung 3, 46-48 air pollution tolerances in trees. In: Genetic e condizioni di ef- Gellini R (1989) Inquinamento Effects of Air Pollutants in Forest Tree Popu- lations (Scholz F, Gregorius HR, Rudin D, ficienza del bosco. Economia Montana, Linea eds) Springer-Verlag, Berlin, 29-37 Ecologica 6, 11-22