The effects of phytotoxic gases on native Australian plant species: Part 1. Acute effects of sulphur dioxide

THE EFFECTS OF PHYTOTOXIC GASES ON NATIVE AUSTRALIAN P L A N T S P E C I E S : P A R T I. A C U T E EFFECTS OF SULPHUR DIOXIDE

J. A. O'CONNOR, D. G. PARBERY& W. STRAUSS

University o f Melbourne, Parkville, Victoria 3052, Australia

ABSTRACT

Relative susceptibility to acute S 0 2 injury has been determined for seedlings of 131 Australian tree and shrub species, many widely used in urban plantings. Acute injury was seen to occur in sensitive species of Eucalyptus and Acacia after 3 h exposure to 1 ppm of SO z in filtered air. O f those tested, Eucalyptus species appeared to be the most sensitive and Casuarina species the most resistant. Other genera studied included Acacia, Banksia, Callistemon, Callitris, Hakea and Melaleuca.

INTRODUCTION

Damage to ornamental, forest and agricultural plant species, resulting from exposure to air pollutants, is already a world-wide problem, and is increasing in heavily industrialised and densely populated areas (Heggestad, 1968). Research into the effects of toxic gases on vegetation has been reviewed in recent years by several authors, including Scurfield (1960), Thomas (1961), Convoy (1962), Brandt & Heck (1968), Heggestad (1968) and Treshow (1970). While the amount of damage to Australian vegetation is limited when compared with that reported from Europe, Japan and the USA, it appears to be increasing. Went (1956) noted 'unmistakable smog damage' due to photochemical oxidants in Sydney and Melbourne, fluoride damage to vegetables near a Tasmanian superphosphate plant, and 'wholesale destruction of vegetation' around a Tasmanian smelter emitting SO2. Scurfield (1960) reported fluoride damage to Tasmanian Eucalyptus forest near an aluminium works; more recently, White (1962) in Sydney described oxidant smog damage to winter grass (Poa annua), tomatoes, tobacco, petunia and barley, while Hartigan (1970) observed possible oxidant damage to Norfolk Island pine along Sydney beach reserves. 7 Environ. Pollut. (7) (1974)--© Applied Science Publishers Ltd, England, 1974 Printed in Great Britain

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J . A . O'CONNOR, D. G. PARBERY, W. STRAUSS

Total oxidant concentration in the surface air over Sydney has attained 17 pphm for a one-hour average (NSW Department of Public Health, 1961-71), and in Melbourne 9 pphm has been recorded in a bayside suburb (Galbally, 1972). Chronic exposure to daily ozone levels as low as 5 pphm has been seen to induce premature leaf senescence in some sensitive plants, e.g. Pinto bean (Engle & Gabelman, 1967). In general, however, SO2 levels have remained low in Melbourne (Victorian Department of Health, 1961-72), Sydney (NSW Department of Public Health, 1961-71), and in Brisbane (Air Pollution Control Council of Queensland, 1971-72). SO2 concentrations (30 min average) have very occasionally attained 15 pphm in parts of Melbourne (O'Heare, 1972), and maximum 24 h average SO 2 concentrations of 18.5 pphm have been recorded in Wollongong (NSW Department of Public Health, 1961-71). Applegate & Durrant (1969) found the highly susceptible Spanish peanut to be injured by 5 to 12 pphm after 4 to 8 h fumigation, and Berry (1970) observed that sensitive clones of Eastern white pine were injured by 8 h exposure to 10 pphm SO 2 under certain conditions. However, acute injury does not normally occur to sensitive plants below 25-30 pphm exposure over an indefinite time period, while chronic injury may occur at concentrations between 10 and 30 pphm SO2, under continuing high-sensitivity conditions of exposure (Brandt & Heck, 1968). These levels do not widely prevail in Australian urban areas. When SOz is accompanied by another pollutant, lower concentrations of either gas can sometimes injure plants. For example, Applegate & Durrant (1969) showed that a 'synergistic' combination of 0.8 to 1.0 pphm ozone and 2 to 3 pphm SO 2 caused acute injury to Spanish peanut; acute injury was reported by Hindawi (1968) on tobacco exposed to a mixture of 3 pphm ozone with 10 pphm SO2. Prevailing Australian urban SO/ and oxidant levels could therefore be responsible for plant damage already noted. Since Eucalyptus and Acacia species are grown in California (USA), Israel, Italy, Spain, Portugal and South Africa, as well as in Australian cities, a series of investigations into the acute and chronic effects of air pollutants on a range of Australian tree and shrub species has been commenced. This paper reports preliminary observations, following exposure of young plants to various concentrations of SO 2, for various times, under controlled high sensitivity environmental conditions.

MATERIALS AND METHODS

Plants'were fumigated in a 50 ft 3 (1.42 m 3) naturally-illuminated chamber (see Fig. 1), based on design principles suggested by Heck et al. (1970). A turbulent air/SO 2 mixture was blown into the chamber through the base, and was exhausted

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN PLANTS

,s

Ti2

9

I

t

'

Fig. 1. Diagrammatic transverse section through fumigation system. I. SO2 bottle. 2. 3.2 mm/SO2 inlet tube. 3. Activated carbon filter, 46 cm x 30 cm × 2.5 cm. 4. 'Multivane' 450 cfm blower. 5. Excess gas slide control. 6. Fumigation mixture slide control. 7. 76 mm i.d. gas inlet duct. 8. Pitot/monometer, for monitoring air flow.

9. Hygrothermograph (temperature and RH). 10. Water in base (for RH control). 11. Pegboard gas distributor. 12. Chamber exit ports. 13. Polyester film walls of 50 ft3 chamber. 14. Probe to SO2 monitor. 15. Beckman 0-4 ppm SO2 monitor. 16. Three-speed chart recorder. 17. Trolley. 18. Section through container of plants.

Relative humidity was maintained in the 6 0 ~ - 7 0 ~ range by periodic spraying of the pegboard floor. t h r o u g h p o r t s a r o u n d the roof-line. A i r flow-rate past test-plant foliage was 2 m/rain, with 2 c o m p l e t e air changes/min, W i t h the c h a m b e r o p e r a t i n g u n d e r full sunlight d u r i n g late spring, internal t e m p e r a t u r e and relative h u m i d i t y were m a i n t a i n e d in the ranges 20°C to 27°C a n d 609/00 to 7 0 ~ , respectively. CO2 levels were 9 5 ~ or m o r e o f a m b i e n t external c o n c e n t r a t i o n ( a p p r o x i m a t e l y 330 to 340 p p m ) (Attiwiil, personal c o m m u n i c a t i o n ) . Test p l a n t s were g r o w n at high water availability, in well-drained s a n d y l o a m soil. F u m i g a t i o n s were carried o u t d u r i n g the midm o r n i n g to early a f t e r n o o n period, plants generally being less sensitive later in the day, when leaf sugar c o n t e n t is high a n d p h o t o s y n t h e t i c activity is below m a x i m u m . T h e physical c o n d i t i o n s simulated in the c h a m b e r a p p r o x i m a t e d those likely to occur periodically in a n d a r o u n d the large A u s t r a l i a n cities d u r i n g spring, s u m m e r and autumn. A h y g r o t h e r m o g r a p h r e c o r d e d t e m p e r a t u r e a n d h u m i d i t y within the c h a m b e r ; SO 2 levels were m e a s u r e d using a B e c k m a n M o d e l 906 A m o n i t o r with three-speed c h a r t recorder. Airflow t h r o u g h the inlet d u c t was m o n i t o r e d by a traversing pitot t u b e with 0-250 Pa m a n o m e t e r .

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J . A . O'CONNOR, D. G. PARBERY, W. STRAUSS

Air was filtered into the system through a 25 m m bed of activated charcoal, designed to adsorb ambient phytotoxic gases and particulates. SO2 was added at concentrations of 0.3 ppm (800/~g/m3), 1 p p m (2620/~g/m3), 2 ppm (5240/~g/m 3) and 3 ppm (7860/~g/m3). Durations of fumigations were 0.5, I, 2, 4 and 6 h at the 3 ppm SO2 level; 4 h at 2 ppm SO2; 3 and 6 h at 1 ppm SO2. In addition, one 27 h fumigation at 0.3 ppm SO2 (800 pg/m 3) was carried out. Sets of 3 to 9 months old plants, grown from seed in polythene or wood-veneer tubes 5 cm diameter x 15 cm length, placed in buckets containing well-drained sandy loam, were used for most fumigations. Table 1 lists the genera and number of TABLE 1 AUSTRALIAN GENERA FUMIGATED WITH SO2

Genus Acacia Agonis A Ibizzia Angophora Banksia Braehychiton Callistemon

Number o f species 27

1 1 1 5 1 7

Genus Callitris Casuarina Correa Eucalyptus Eugenia Grerillea Hak ea

Number o f species

Genus

Number o f species

4 6 1

Kunzea Lagunaria Leptospermum Melaleuca Myoporum Prostanthera S ynearpia Tristania

3 1 4 15 I 2 1 2

43

1 1 3

species exposed to SO 2- Where possible, each set of 131 species received simultaneous fumigation, to minimise the effects of variations in chamber conditions to plant sensitivity. For most species, 8 or 9 replicates were available for fumigation. One complete set of control plants was exposed to both filtered and unfiltered urban air, for periods of up to 30 h, under conditions similar to those maintained during fumigation.

RESULTS AND DISCUSSION

Relative sensitivities of Australian species to SO 2 are presented in Appendix 1. A sensitivity scale from 0 (unaffected by SO2) to 6 (sensitive to SO2) has been used, based on fumigation times and SO2 concentrations as given in Table 2. The wide range of plant sensitivity is due primarily to differences in rates of foliar absorption of SO 2, resulting from varying rates of leaf physiological activity (Thomas, 1961). In these experiments, sensitivities were compared by estimating the percentage of necrotic leaf tissue produced by exposure to S O 2 - - a method widely used as an index of plant injury. The proportion of necrotic tissue was estimated from visual inspection of the small plants, 3 or 4 days after fumigation, when injury was fully developed.

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN

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TABLE 2 SCALE OF SENSITIVITY OF AUSTRALIAN PLANTS TO SO 2

Symbol

0 1 2 3 4 5 6

% leaf tissue destroyed by exposure to: 1 ppm 8 0 2 2 ppm S 0 2 3 ppm S O 2 for 6 h for 4 h for 4 h

0 0 0-5 0-10 10-20 20-40 >40

Approx. 0 0-10 5-20 10-40 20-60 40-70 >80

Approx. 0 2-25 20-50 40-75 60-100 70-100 80-100

Description

Unaffected Extremely resistant Highly resistant Resistant Moderately resistant Moderately sensitive Sensitive

TABLE 3 TYPICAL SO 2 FUMIGATION RESULTS FOR 7 SPECIES

Acute injury (proportion o f necrotic leaf tissue) after exposure to ." Species

Sensitivity to SOz

2 ppm S02

1 ppm S 0 2

3h Casuarina stricta Melaleuca squamea Acaciapruinosa Callitris glauca Eucalyptus melliodora Melaleuca squarrosa Eucalyptus elata

0

1 2 3 4 5 6

.

6h .

4h .

3ppm S02

0'5h .

. . . . 0.05 -0.20 --0.30 -0 . 2 5 0.50 -0 - 3 0 0.75 0.01 0 - 7 0 0.90

.

. ----0.02

lh .

2h .

. O-Ol --0-02 0.60

4h

6h

O.15 0.30 0.75 0-90 0.60 0.95

0.25 0.50 0-75 1.00 0.75 0.95

.

0.20 0.01 0.02 0'50 0.95

Typical results for one species from each of the 7 sensitivity classes are given in T a b l e 3. Sensitive species, injured by exposure to 1 ppm S O / , exhibited s y m p t o m s of acute injury 2-3 h after exposure to high levels. F o r example, for A c a c i a p y c n a n t h a , s u n k e n water-soaked dull green areas were evident on injured leaves 2 h after fumigation with 3 p p m SO2 : this is due to loss of cellular capacity to retain water, with diffusion of cell sap through intercellular spaces (Treshow, 1970). T w e n t y - f o u r hours after fumigation, desiccation a n d death of injured areas had occurred and leaf colours had changed to pale tan through to deep red-brown, the final colour a p p e a r i n g species-specific. Leaf abscission usually occurred in small-leaved or pinnately leaved species within 4 days of injury, a n d frequently after only 3 days. In larger-leaved species, even when 70 % or m o r e leaf necrosis had occurred, leaf abscission was c o m m o n l y n o t completed for 2 weeks. Regrowth of injured plants occurred m a i n l y from apical shoots, and from axillary buds where leaf abscission had occurred. I n j u r y occurred most rapidly and extensively to fully-developed activelyphotosynthesising leaves of the y o u n g plants, due p r o b a b l y to the a c c u m u l a t i o n of

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J. A. O'CONNOR, D. G. PARBERY, W. STRAUSS

toxic sulphite at a rate exceeding cellular capacity to convert it to the far less toxic sulphate (Brandt & Heck, 1968). Young expanding leaves at the shoot apices were more resistant, and were rarely destroyed, even by 4 or 6 h exposure to 3 ppm SO2. At this level of exposure, total leaf destruction occurred in some Eucalyptus species (E. aggregata, E. st. johnii, E. crenulata, E. melliodora), and in Kunzea ericifolia. Nearly complete destruction was observed in E. astringens, E. baxteri,

E. bosistoana, E. cladocalyx, E. forrestiana, E. globulus, E. gomphocephala, E. nicholii, E. occidentalis, E. polyanthernos, E. radiata, E. regnans, E. robusta, E. rubida, E. saligna, E. spathulata, E. viminalis, and in one species of Acacia (A. buxifolia). Seedling death was observed in some sensitive Eucalyptus species, following total leaf loss resulting from exposure to high SO2 levels (3 ppm, 4 to 6 h). This occurred in E. regnans, E. radiata, E. nicholii, E. st. johnii, E. melliodora and E. viminalis. No highly-sensitive species, liable to acute SO2 injury at the 0.3 ppm level of exposure, were detected. Sensitive species, with 70 ~o or more of leaf tissue destroyed by exposure to 1 ppm of SO 2 for 3 to 6 h, were Eucalyptus elata, E. camaldulensis, E. radiata, E. regnans and E. saligna. Species measuring 50 ~ or more leaf destruction at these levels were E. crenulata, E. rnacrorhyncha, E. nicholii and E. polyanthemos. In addition, a few resistant species occurred in the genus Eucalyptus: E. globulus, E. rnaculata, E. ovata, E. tetraptera and E. urnigera. Other highly-resistant species were Casuarina cristata, C. cunninghamiana, C. stricta and C. torulosa, Acacia oxycedrus, A. sophorae and Lagunaria patersonii, all uninjured by 4 or 6 h exposure to 3 ppm SO2. Almost as resistant were Kunzea

baxteri, Acacia dealbata, A. terminalis, A. longifolia, Callitris oblonga, Hakea laurina, H. petiolaris, Melaleuca halmaturorum, M. squamea, Myoporum insulare and Syncarpia laurifolia, only slightly injured by the above high concentrations of SO2. Some species, severely injured by exposure to high SO2 concentrations, showed unexpectedly high resistance to somewhat lower SOz levels; such species are not readily classified into the sensitivity grades described in Table 2. For example, Eucalyptus globulus sustained only 5 ~o leaf necrosis after 4 h exposure to 2 ppm, but lost 100~o of leaf tissue after 4 h exposure to 3 ppm. However, there was generally good correlation between low threshold of injury and complete leaf destruction at higher concentrations; a typical example was Eucalyptusforrestiana, sustaining 30~o leaf necrosis after 6 h exposure to 1 ppm SO2, and 9 9 ~ necrosis after 4 h at 3 ppm. No evidence of acute or chronic injury, premature leaf abscission, or any other abnormality, was observed in sets of control plants, or in sets of plants exposed to 0-3 p p m of SO2 for 27 h.

Appearance of injured foliage (a) Dicotyledonous species: Initial acute symptoms, resulting from exposures at, or slightly above, the species' injury threshold, usually appeared as leaf tip or

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN PLANTS

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marginal necrosis, sharply delimited from uninjured green areas. Less commonly, initial injury appeared as marginal, intercostal or irregular flecks of necrotic tissue on middle or lower leaves (in approximately one-half of the Eucalyptus species tested). A few species, e.g. Eucalyptus viridis, initially developed basal leaf necrosis. At higher concentrations, leaf necrosis tended to be intercostal, extending inwards from tip and margin, and was confined to irregular areas between the larger veins. In leaves with lesions over more than 50 ~ of surface area, surviving tissues mostly occurred along midrib and main veins. Occasionally diffuse chlorotic margins developed, or chlorosis of otherwise unaffected leaves (e.g. Eugenia smithii, Acacia dealbata, Acacia oxycedrus). Veinal injury was not observed. (b) Callitris spp. : Injury resembled symptoms described by Treshow (1970) for needle-leaved coniferous species. Two to three days after exposure, apical necrosis of needles appeared, and extended gradually towards their bases. Injury was most evident on new growth. Colour varied from light tan (C. endlicheri) to deep redbrown (C. glauca). (c) Colour of necrotic tissues: This varied widely between species, but was constant for any given species; O'Connor (1973) includes a pictorial atlas of SO2 injury to Australian plants. Colours and injury patterns were characteristic of acute SO2 injury, described for a range of plants (Treshow, 1970; Brandt & Heck, 1968). Colours ranged from pale bleached tan (e.g. Prostanthera spp.), through light tan (e.g. Eucalyptus saligna), medium tan (Banksia spp.), dark tan (Callistemon spp.), red-brown (Acacia decurrens), dark brown (Hakea laurina), to deep red (Acacia

pruinosa). Some genera (e.g. Acacia, Eucalyptus) displayed wide intra-species variation of necrotic colour. Other genera tended to be uniform: Banksia (medium tan), Kunzea (light tan), Melaleuca (light or medium tan).

Variation in sensitivity within species Within single species, which are genetically heterogeneous, it is not surprising to find considerable variation in sensitivity to SOz. For example, one seedling of Eucalyptus gomphocephala sustained 6 0 ~ leaf necrosis after 1 h exposure to 3 ppm SO2; another seedling sustained only 40 ~ necrosis after 2 h exposure to the same concentration. For a few cases, two different sets of plants grown from seed from different districts were available for simultaneous fumigations. These also showed considerable variability: e.g. Melaleuca incana, 5 ~o and 80 ~o necrosis after 4 h exposure to 3 ppm SO2; Acacia pravissima, 2 0 ~ and 7 0 ~ necrosis after 4 h exposure to 2 ppm SO2 ; Agonisflexuosa, 20 ~ and 85 ~o necrosis after 4 h exposure to 3 ppm SOz (in this latter case, plants were aged 12 months and 3 months, respectively). Eucalyptus viminalis var. racemosa was more sensitive than other varieties tested at i ppm SO2, but was far less sensitive at the 2 ppm and 3 ppm levels. However, two sets of Brachychiton populneus, Acacia decurrens and Eucalyptus viminalis, reacted similarly to all treatments.

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J. A. O'CONNOR, D. G. PARBERY, W. STRAUSS

Since all fumigations could not be performed under the same environmental conditions, it was impossible to separate variation in genetic sensitivity (apart from the species discussed above) from that due to environmental or physiological changes. However, the majority of species showed a reasonably uniform increase in sensitivity with increasing SO2 concentrations, and increasing durations of exposure. This indicated that relative sensitivities would not vary greatly if fumigations were repeated on different batches of plants.

Variation in sensitivity between genera Genera with 5 or more species are briefly reviewed below. (i) Acacia (27 species tested): Sensitivity was very variable among Acacia spp., ranging from the extremely resistant A. oxycedrus which was almost unaffected by 4 h exposure to 3 ppm SO2, to the moderately sensitive A. howittii, measuring 20 necrosis after 3 h exposure to 1 ppm SO2. (ii) Banksia (5 species tested): This was a much more uniformly sensitive genus, although B. serrata was considerably less sensitive to a 4 h 3 ppm exposure than the other 4 species tested. (iii) Callistemon (7 species tested): A moderately resistant genus, with no injury observed at 1 ppm SOz, 6 h exposure. C. pinifolius, C. citrinus and C. violaceus possessed greater resistance than the other 4 species, at 2 ppm SO/. (iv) Callitris (4 species tested): This genus showed a large variation in resistance --all species were uninjured at I ppm, C. glauca showing 30 ~ injury at 2 ppm, 6 h, compared with 5 ~ injury to C. oblonga after 6 h, 3 ppm. (v) Casuarina (6 species tested): This was the most resistant genus, and the most uniformly insensitive. Only 2 species (C. glauca and C. littoralis) showed even slight injury after exposure to 3 ppm S O / f o r 4 h. (vi) Eucalyptus (43 species tested): This was the most sensitive genus tested, showing the widest range in susceptibility to acute SO 2 injury; it includes a few extremely resistant species (E. maculata, E. urnigera, E. botryoides, E. tetraptera), and many of (probably) Australia's most sensitive species, severely injured by 3 or 6 h exposure to 1 ppm of SO2. (vii) Melaleuca (15 species tested): M. squarrosa had the lowest injury threshold ( < 1 ppm for 6 h), but was more resistant to high-level exposure (3 ppm, 4 h) than were M. ericifolia (almost complete leaf destruction after 2 ppm, 4 h), M. decussata, M. elliptica, M. linari(folia, M. lanceolata and M. styphelioides.

Possible synergism : SO z acting with unfiltered air A fumigation at 3 ppm of S O 2 for 4 h, carried out with all plants on 31 October 1972, is of particular interest due to the unexpectedly high degree of injury caused to many plants. This fumigation was performed under low light intensity, at a lower temperature, with fully overcast skies, under sensitivity conditions classed as

P H Y T O T O X I C GASES A N D N A T I V E A U S T R A L I A N P L A N T S

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TABLE 4 EXAMPLES OF INJURIES CAUSED TO SOME SPECIES AFTER FUMIGATION UNDER TWO'DIFFERENT SETS OF ENVIRONMENTAL CONDITIONS

Species fumigated

(1)

Acacia iteaphylla Acacia triptera Angophora costata Brachychiton populneus Callistemon citrinus Callistemon sa[ignus Eucalyptus astringens Eucalyptus viridis Melaleuca lateritia Melaleuca lanceolata Acacia baileyana Acacia floribunda Acacia pycnantha Acacia sophorae Eucalyptus obliqua Leptospermum laevigatum Melaleuca squamea Prostanthera ovalifolia

40 30 20 5 3 1 50 50 2 30 95 75 90 50 90 50 25 98

°/o o leaf necrosis

(2) 75 60 70 20 75 80 98 75 50 80 70 40 50 15 60 15 15 75

Possible synergistic effects

Anticipated pattern of injury

1

(1) High sensitiL,ity conditions: 3-0 5_ 0.2 ppm S02, 6 h, 1200-1800 h, mean 24.5°C, 72~ relative humidity, full sunlight. SOz added tofiltered urban air. (2) Moderate sensitivity conditions." 3.0 ± 0"15 ppm S02, 4 h, 1200-1600h, mean 18.5°C, 68~o relative humidity, overcast-dull light. S02 added to unfiltered urban air.

'moderate'. However, injury produced in many species exceeded that from a previous fumigation at 3 ppm SO2, for 6 h ( 5 0 ~ longer duration), under high sensitivity conditions, including strong sunlight, carried out on 30 September 1972. Examples are given in Table 4 to illustrate both types of response. Both fumigations began at 1200 h ; relative humidites were approximately 70 ~ ; median temperatures were approximately 24°C (high light fumigation), and 18.5°C (low light fumigation). All other conditions (airflow, etc.) were the same. The significant difference appeared to be the use of unfiltered air for the 'moderate sensitivity' fumigation. It is possible that S O / w a s acting synergistically with some component of the unfiltered air (possibly traces of photochemical oxidants), to produce abnormally high injury levels in some species. However, variation of SO2 sensitivity within a species could also account for some of the increase in injury observed under low light conditions. Infra-red photograph)'

Bravo (1972) demonstrated a decrease in reflectance in the 500m/~ to 900 m/a infra-red range from foliar mesophyll tissues injured by ozone. This was detected using infra-red sensitive film, 48 h prior to the appearance of visible injury in fumigated leaves of Clintland oats.

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J . A . O"CONNOR, D. G. PARBERY, W. STRAUSS

Thomas (1956) summarised experimental results showing that photosynthetic activity was reduced by SO2 levels too low to cause visible injury. In an attempt to detect possible cellular changes accompanying this reduction, a series of paired photographs was made of Banksia integrifolia plants (15 months old), using films sensitive to infra-red and visible wavelengths, during the period 0-40 h after fumigation with 3 ppm SO2. No prior evidence of SOz injury was observed when comparing infra-red and daylight photographs. Oat leaves do not possess a palisade cell layer; in B. integrifolia this layer could tend to mask any possible loss of infra-red reflectance from underlying highly-reflective mesophyll tissues. However, it appears that infra-red photography may be less suitable for early detection of SOz injury than for oxidant damage to plants.

Field implications It is considered that the relative sensitivities demonstrated between species would be reflected to a considerable extent in field vegetation exposed to SO2 pollution episodes, under 'high sensitivity' conditions similar to those maintained in the fumigation chamber. However, the results of the experiments must be applied with discretion to the general environment for the following, viz: (i) Young plants, with the exception of seedlings of conifer and occasional other species such as Populus tremuloides (Gordon & Gorham, 1963), tend to be less sensitive to SOz than mature plants (Treshow, 1970). (ii) There is some evidence for a midday decrease in sensitivity to SO2 (Brandt & Heck, 1968); thus, some species could have greater sensitivity to SOz than is indicated by these experiments. (iii) A large number of environmental variables have been shown to affect susceptibility to SO2; for example, sensitivity generally increases with light intensity up to full sunlight, with increased relative humidity up to 100K, and with temperature increase accompanying higher light intensities. On the other hand, sensitivity tends to decrease when plants are growing under even a slight water stress or in fertile soils--particularly under high nitrogen conditions (Treshow 1970). (iv) Relative species sensitivity under chronic, low-level exposure to SOz need not necessarily follow the pattern observed during exposure to relatively high concentrations which result in acute injury. (v) Varieties of some species would be expected to show wide variation in sensitivity to SO2, while other species would have more constant sensitivity factors (Thomas, 1961). ACKNOWLEDGEMENTS

A preliminary study, developing some of the techniques used, was ~arried out by Mr C. Martin and Mrs A. Fisher. The Forests Commission of Victoria and the

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN PLANTS

17

Natural Conservation League of Victoria assisted in the supply of Australian native plants. The authors wish also to express their appreciation to the SECV Hermann Research Laboratory, and, in particular, Mr J. O'Heare and Mr J. McCulloch, for the use of the SO2 recorder. One of the authors (J. O'C.) was granted leave by the Preston Institute of Technology to enable him to carry out the investigation. REFERENCES APPLEGATE, H. G. t~¢, DURRANT, L. C. (1969). Synergistic action of ozone-sulphur dioxide on peanuts. Enriron. Sci. & Technol., 3, 759-60. BERRY, C. (1970). In Environment andplant response, by M. Treshow, Ch. 15, Sulphur dioxide, 252. New York, McGraw-Hill. BRANDT, C. S. & HECK, W. W. (1968). Effects of air pollution on vegetation. In Air pollution, ed. A. Stern, 1,401-43. New York, Academic Press. BRAVO, H. A. (1972). The use of color infrared photography in the detection of non-visible injury to vegetation by ozone. Proc. Clean Air Conf., Melbourne, 1972, 268-73. Clean Air Society of Australia and New Zealand. CONROY, R. J. (1962). The effects of air pollution on vegetation. Proc. Clean Air Conf., Unit,. N S W , 19-21 February, 1962, 1, Paper No. 8. ENGLE, R. L. & GABELMAN,W. H. (1967). The effects of low levels of ozone on pinto beans, Phaseolus rulgaris L. J. Am. Soc. hort. Sci., 91,305-9. GALBALLY, I. E. (1972). Ozone and oxidants in the surface air near Melbourne, Victoria. Proc. Clean Air Conf., Melbourne, 1972, 192-8. Clean Air Society of Australia and New Zealand. GORDON, A. G. & GORH'AM, E. (1963). Ecological aspects of air pollution from iron sintering plant in Wawa, Ontario. Can. J. Bot., 41, 1064-78. HARTIGAN, D. (1970). Disorder affecting Norfolk lsland pines along Sydney beaches. NSW Government Printer, Publication No. M.18500. HECK, W. W., DUNNING, J. A. & JOHNSON, H. (1970). Design o f a simple plant exposure chamber. US Department of Health, Education & Welfare, National Center for Air Pollution Control, APTD-68-6. HEGGESTAD, H. E. (1968). Diseases of crops and ornamental plants incited by air pollutants. Phytopathology, 58, 1089-97. HINDAWI, 1. J. (1968). Injury by sulfur dioxide, hydrogen fluoride and chlorine as they were observed and reflected on vegetation in the field. J. Air Pollut. ControlAss., 18, 307-12. NSW DEPARTMENT OF PUBLIC HEALTH (1961--1971). Annual results o f air pollution monitoring in New South Wales, 1970 and 1971. Division of Occupational Health and Pollution Control, Lidcombe, NSW. O'CONNOR, J. A. (1973). The sensitA'ity o f Australian natiue plants to sulphur dioxide. M.App.Sci. Thesis, University of Melbourne. O'HEARE, J. N. (1972). Air quality measurements in the Williamstown-Port Melbourne area. Proc. Clean Air Conf., Melbourne, 1972, 169-75. Clean Air Society of Australia and New Zealand. QUEENSLAND AIR POLLUTION CONTROL COUNCIL (1971-72). Annual report A.59--1972. Government Printer, Brisbane, Queensland. SCURFIELD,G. (1960). Air pollution and tree growth. For. Abstr., 21,339-47; 517-28. THOMAS, M. D. (1956). The invisible injury theory of plant damage. J. Air Pollut. Control Ass., 5, 205-6. THOMAS, M. D. (1961). Effects of air pollution on plants. Monograph Set. WHO, 46, 233-77. TRESHOW, M. (1970). Environment and plant response. Ch. 15, Sulfur dioxide, 245-66; Ch. 18, Ozone and plants, 322-83. New York, McGraw-Hill. VICTORIAN DEPARTMENTOF HEALTH (1961-1972). Air pollution monitor results in Victoria, published annually. Clean Air Division, General Health Branch, Melbourne. WENT, F. W. (1956). Some aspects o f plant research in Australia: A report on a visit to Australia, July-Oct. 1955. Melbourne, CSIRO. WHITE, N. H. (1962). Observations on air-oxidant injuries on plants in the Sydney metropolitan area. Proc. Clean Air Conf., Unit'. N S W , 19-21 February 1962, 1, Paper No. 7.

18

J. A. O'CONNOR, D. G. PARBERY, W. STRAUSS

APPENDIX I RELATIVE SENSITIVITIES OF AUSTRALIANPLANT SPECIES EXPOSED TO SO 2

Species

Common name

Sensitivity (see Table 2)

Acacia ( T o u r n . ) L. Fam. Leguminosae

A. accola

W a l l a n g a r r a wattle

2

C o o t a m u n d r a wattle

3

Box-leaf wattle

4

Wallowa

3

W y a l o n g wattle

2

Silver wattle

1

Q u e e n or early black wattle

3

D r u m m o n d ' s wattle

2

Catkin wattle

1

H a i r y - p o d wattle

2

Sticky wattle

2

Gawler R a n g e wattle

3

Sallow wattle

1

Blackwood

2

Myrtle wattle

3

Spike wattle

0

M o u n t M o r g a n ( Q u e e n s l a n d silver) wattle

1

O v e n s wattle

5

G o l d e n rain wattle

5

Frosty wattle

2

G o l d e n wattle

2

Wirilda

2

W e s t e r n wreath wattle

1

C o a s t wattle

1

C e d a r wattle

1

M a i d e n & Betche

A. baileyana F. Muell.

A. buxiJblia A. C u n n .

A. calamifolia Sweet

A cardiophylla A. C u n n , ex Benth.

A. dealbata Link

A. decurrens Willd.

A. drummondii Benth.

A. floribunda Sieb.

A. glandulicarpa Reader

A. howittii F. Muell.

A. iteaphylla F. Muell. (syn. A. neriifolia A. C u n n . )

A. Iongifolia Willd.

A. melanoxylon R. Br.

A. myrtifolia Willd.

A. oxycedrus Sieb.

A. podalyriaefolia A. C u n n .

A. pravissima F. Muell.

A. prominens A. C u n n .

A. pruinosa A. C u n n .

A. pycnantha Benth.

A. rhetinodes Schlecht

A. saligna Wendl.

A. sophorae R. Br.

A. terrninalis (Salisb.) MacBride (syn. A. elata A. C u n n . ex Benth.)

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN PLANTS RELATIVE SENSITIVITIES OF AUSTRALIAN PLANT SPECIES EXPOSED TO

Species A. triptera Bth, A. verniciflua A. Cunn. Agonis Lindl. Faro. Myrtaceae ,4. flexuosa Lindl. A. flexuosa Lindl. Albizzia Durazz. Fam. Legurninosae A. Iophantha Benth. Angophora Cav. Faro. Myrtaceae A. costata Domin. (syn..4. lanceolata Cav.) Banksia L.f. Faro. Proteaceae B. collina R . Br. B. ericifolia L.f. B. integrifolia L.f. B. marginata Cav. B. serrata L.f. Brachychiton Schott & Endl. Faro. Sterculiaceae B. populneus R . Br. Callistemon R. Br. Faro. Myrtaceae C. citrinus Stapf. (syn. C. lanceolatus Sweet) C. lilacinus Cheel (syn. C. violaceus) C. pinifolius Sweet C. phoenieeus Lindl. C. salignus Sweet C. viminalis G. D o n C. violaceus Callitris Vent. Faro. Coniferae C. collumellaris F. Muell. (syn. C, glauea R. Br.)

Common name

19

S02--eontinued Sensitivity (see Table 2)

Spur wing wattle

1

Varnish wattle

6

Willow myrtle

2

Willow myrtle

1

Cape wattle

2

Apple myrtle (rusty gum)

Hill or hair pin banksia

5

Heath banksia

4

Coast banksia

4

Silver banksia

5

Saw banksia

1

Currajong

1

Crimson bottlebrush

3

Lilac bottlebrush

3

Pine-leaved bottlebrush

3

Fiery bottlebrush

4

Pink-tip bottlebrush

3

Weeping bottlebrush

4

Violet bottlebrush

3

Murray cypress-pine

3

J. A. O'CONNOR, D. G. PARBERY, W. STRAUSS

20

RELATIVE SENSITIVITES OF AUSTRALIAN PLANT SPECIES EXPOSED TO

Species C. endlicheri (Patio F. M. Bailey (syn. C. calcarata R. Br.) C. oblonga Rich C. rhomboidea R, Br. Casuarina L. Fam. Casuarinaceae C. cristata Miq. C. cunninghamiana Miq. C. glauca Sieber C. littora6s Salisb. (syn. C. suberosa Otto & Dietr.) C. stricta Dryand C. torulosa Dryand Correa Andr. Faro. Rutaceae C. reflexa (Labill.) Vent. Eucalyptus L'Heritier Faro. Myrtaceae E. aggregata Deane & Maiden E. astringens Maiden E. baxteri (Benth.) Maiden & Blakely E. bosistoana F. Muell. E. botryoides Sm. E. ealophylla R. Br. ex Lindl. var. 'rosea' E. camaldulensis Dehn. E. chapmaniana Cameron E. cladocalyx F. Muell. E. cosmophylla F. Muell. E, crenula'ta Blakely ex de Beuz. E. elata Dehnh. (syn. E, andreana Naudin) E.ficifolia F. Muell.

Common name

SO2--continued Sensitivity (see Table 2)

Black cypress-pine

1

Tamar cypress-pine

1

Oyster Bay cypress-pine

3

Belah

0

River she-oak

0

Grey buloke (Swamp she-oak)

1

Black she-oak

1

Drooping she-oak

0

Rose she-oak

0

Common correa

3

Black gum

5

Brown mallet

5

Brown stringybark

5

Coast grey box

4

Southern mahogany gum

3

Pink marri

3

River red gum

6

Bogong gum

4

Sugar gum

4

Cup or bog gum

5

Silver or Buxton gum

6

River peppermint

6

Red flowering gum

2

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN PLANTS RELATIVE SENSITIVITIES OF AUSTRALIAN PLANT SPECIES EXPOSED TO

Species E. forrestiana Diels E. globulus Labill E. gomphocephala A. DC. E. "gummifera (Gaertn.) Hochr. E. kitsoniana (Luehm.) Maiden E. macrorhyncha F. Muell. E. maculata Hook E. melliodora A. Cunn. ex Schau. E. nicholii Maiden & Blakely E. obliqua L'Herit E. occidentalis Endl. E. ovata Labill. E. pauciflora Sieb. ex Sreng. E. perriniana F. Muell. ex Rodway E. platypus Hook E. polyanthemos Schau. E. radiata Sieb. ex DC. E. regnans F. Muell. E. risdonii Hook. f. E. robusta Sm. E. rubida D e a n e & Maiden E. saligna Sm. E. sideroxylon A. Cunn. ex Woolls vat. 'rosea' E. spathylata Hook E. st. johnii R. T. Baker (syn. E. bicostata Maiden et al.) E. tetraptera Turcz. E. urnigera Hook. f.

Common name

21

SO2--continued Sensitivity (see Table 2)

Forrest's marloch (Fuchsia gum)

6

Southern blue gum

1

Tuart

5

Red bloodwood

3

Bog gum or Gippsland Mallee

3

Red stringybark

5

Spotted gum

0

Yellow box

4

Willow-leaved peppermint

6

Messmate

3

Swamp yate

5

Swamp gum

1

White sallee

4

Spinning gum

5

Round-leaved moort

3

Red box

6

Narrow leaf peppermint

6

Mountain ash

6

Silver peppermint

5

Swamp mahogany

4

Candlebark

5

Sydney blue gum

5

Red ironbark

4

Swamp mallet

3

St John's blue gum

5

Four-winged mallee

1

Urn gum

0

J. A. O'CONNOR, D. G. PARBERY, W. STRAUSS

22

RELATIVE SENSITIVITIES OF

AUSTRALIANPLANT SPECIES

Species E. viminalis Labill. E. viminalis Labill. var. racemosa E. viridis R. T. Bak. Eugenia Mich. Fam. Myrtaceae E. smithii Grevillea R. Br. Fam. Proteaceae G. robusta A. Cunn. Hakea Schrad. Fam. Proteaceae H. laurina R . Br. H. petiolaris Meissn. H. saligna Knight Kunzea Reichb. Fam. Myrtaceae K. ambigua Druce K. baxteri (Klotzsch) Schau. K. muelleri Benth. (syn. K. ericifolia F. Muell.) Lagunaria G. Don. Fam. Malvaceae L. patersonii G. Don. Leptospermum Forst. Fam. Myrtaceae L. laevigatum F. Muell. L. lanigerum (Ait.) Sm. (syn. L. pubescens Lam.) L. obovatum Sweet (syn. L. flavescens Smith) L. squarrosum Gaertn. Melaleuca L. Fam. Myrtaceae M . armillaris Smith M . decussata R. Br. M . elliptica Labill. M . ericifolia Smith

EXPOSED TO

Common name

so2--continued Sensitivity (see Table 2)

Manna gum

5

Coastal manna-gum

2

Green mallee

4

Lilly pilly

1

Silky oak

3

Pin-cushion hakea

1

Sea-urchin hakea

1

Willow hakea

2

White kunzea

2

Baxter's kunzea

1

Heath-leaf kunzea

5

Pyramid tree

0

Coastal tea-tree

1

Woolly tea-tree

5

Tantoon

1

Peach-flower tea-tree

2

Bracelet honey-myrtle

3

Cross-leaf honey-myrtle

3

Granite honey-myrtle

2

Swamp paperbark

5

PHYTOTOXIC GASES AND NATIVE AUSTRALIAN PLANTS RELATIVE SENSITIVITIES OF AUSTRALIAN PLANT SPECIES EXPOSED TO

Species M . halmaturorum F. v M . M . huegelii Endl. M . hypericifolia Smith M. incana R . Br. M . lanceolata Otto (syn. M . pubescens Schauer.) M . lateritia Otto & Dietr. M . linariifolia Smith M. squamea Labill. M . squarrosa Donn. M . styphelioides Smith M . thymifolia Smith Myoporum Banks & Solan. Fam. Myoporaceae M . insulare R . Br. Prostanthera Labill. Fam. Labiatae P. nivea A. Cunn. P. ovalifolia R . Br. Syncarpia Tenore Fam. Myrtaceae S. laurifolia Tenore Tristania R. Br. Fam. Myrtaceae T. conferta R. Br. T. laurina R . Br.

Common name

23

sO2--continued Sensitivity (see Table 2)

Kangaroo or salt paperbark

1

Chenillle honey-myrtle

5

Red honey-myrtle

3

Grey honey-myrtle

3

Moonah

5

Robin red-breast bush

2

Flaxleaf paperbark

3

Swamp honey-myrtle

1

Scented paperbark

5

Prickly-leaf paperbark

5

Thyme-leaf honey-myrtle

1

Boobialla

1

Snowy mint-bush

2

Violet-shower mint-bush

4

Turpentine tree

1

Queensland brush box

1

Kanooka

1