Responses to ozone of insects feeding on a crop and a weed species

The influence of ozone on insect herbivore growth and population development was investigated. Fumigation of both pea (Pisum sativum L.) and dock (Rumex obtusifolius L.) at a range of O(3) concentrations between 21-206 nl litre(-1) produced changes in mean relative growth rates of the aphids Acyrthosiphon pisum Harris and Aphis rumicis L. of between 24 and -6% relative to controls. However, there was no evidence of a dose-related response to O(3) fumigation and no clear differences in aphid response when fumigated with the plant on prefumigated or previously unfumigated plant material. It is suggested that this may, in part, be due to the presence of NO contamination during O(3) fumigation. However, the MRGR of dock aphids was found to be greater on new compared to old leaves as well as the increase on the new growth and decrease on the old growth of fumigated plants relative to unfumigated controls. The size of egg batches of the chrysomelid beetle Gastrophysa viridula Degeer were found to be larger, survival and productivity of larvae was higher, and the food consumption lower on R. obtusifolius fumigated with 70 nl litre(-1) O(3) compared with unfumigated controls. This meant that these beetle larvae consumed less leaf area per mg of production on fumigated leaves probably because of their better nutritional quality and/or reduced leaf defences. However, the rate of development of larvae was similar on fumigated and control plants.     

Effects of reactive hydrocarbons and hydrogen peroxide on antioxidant activity in cherry leaves

One-year-old cherry trees were fumigated with propene and gas-phase hydrogen peroxide, singly and in combination, in controlled-environment chambers for an 8-week period during the summer season. A UV light source was included with the combined propene and hydrogen peroxide regime to provide a source of hydroxyl radicals and ozone, and thus all the constituents of a photochemical smog. Measurements were made of soluble protein concentration and of glutathione reductase activity in leaf extracts from two or three leaf classes in plants from each treatment regime at the end of each fumigation period. Significant increases in soluble protein concentration with respect to the controls were found in plants fumigated with propene and hydrogen peroxide. The occurrence and extent of these differences depended on the leaf class and on the timing of the fumigation period over the summer with respect to bud break. The activity of glutathione reductase was found to be significantly increased in mature lower leaves of plants which had been fumigated with hydrogen peroxide. This effect was independent of the timing of fumigation with respect to bud break. Enzyme activity was also increased in propene and in propene plus hydrogen peroxide treatments, but only when plants were fumigated early in the growth season.     

Secondary effects of air pollution: ozone decreases brown rust disease potential in wheat

Young wheat plants were fumigated with 170 microg m(-3) ozone for 3 days, or with 210 microg m(-3) ozone for 7 days, for 7 hours a day. At the end of the fumigation period the plants were inoculated with brown rust (Puccinia recondita f. sp. tritici) uredospores. The development of new uredospore pustules on fumigated and control plants was evaluated as a measure of rust disease potential. The number of pustules on the ozone fumigated plants was greatly reduced in comparison with the number of plants treated with charcoal-filtered air.     

Influence of ozone air pollution on plant-herbivore interactions. Part 1: Biochemical changes in ornamental milkweed (Asclepias curassavica L.; asclepiadaceae) induced by ozone

A series of fumigation experiments was conducted with bloodflower (Asclepias curassavica L.) in continuous-flow stirred reactors (CSTRs) to elucidate the effects of ozone on foliar concentrations of several primary and secondary plant metabolites relevant to herbivores. Plants 8 weeks of age were subjected to different ozone levels ranging from 0 to 134 nl liter(-1) for exposure periods up to 16 days. Leaves were analyzed for concentration of soluble carbohydrates, starch, free amino acids, soluble protein, total phenolics, and total cardenolides. Significant interactions between the linear effects of ozone concentration and exposure time were found for soluble carbohydrates, amino acids, cardenolides and phenolics. No significant treatment effects could be observed on foliar starch and protein concentration. The metabolic responses of plants to fumigation appeared to be altered by overall plant nutrition. It is possible that the metabolic changes observed in the host plant represent important changes in nutritional quality to insects.     

Nitrate leaching in important crops of the Valencian Community region (Spain)

Seedlings of the salt secreting mangrove Avicennia marina were exposed to fumes of the volatile fraction of light Arabian crude oil (VFCO) under controlled conditions. Rates of salt secretion were determined in leaves fumigated for 0, 3, and 6 h under four different salinity levels (10, 20, 30, and 40 ppt). Studying the effect of these fumigation periods on stomatal resistance and transpiration was restricted to one salinity level (20 ppt). Opposite to salinity, increasing the fumigation period significantly reduced both salt secretion and transpiration with a significant increase in the stomatal resistance to gas diffusion. During the first day of recovery from fumigation stress, different stomatal oscillation patterns were observed in the treated plants. The amplitude of the oscillations increased with the duration of fumigation. as did the time required for stomatal recovery. Seedlings fumigated for 3 h started to recover within 48 h, while full recovery in seedlings fumigated for 6 h required almost twice that period. The apparent recovery process was evident in the damping off of the amplitude of stomatal oscillations during the measurements period. Data presented herein show that the exposure of mangrove seedlings to VFCO disturbs the normal functions of two major structures in the leaves, i.e. the stomata and the salt glands. The ecophysiological significance of these results was discussed in relation to previous studies.     

Air pollution and agricultural aphid pests. I: Fumigation experiments with SO2 and NO2

A wide range of aphid/host-crop systems was surveyed by means of fumigation experiments in closed chambers for sensitivity to SO(2) and NO(2) at a concentration of 100 nl litre(-1). Aphid performance was measured by the mean relative growth rate (MRGR) of individual aphids. In all cases, except for Acrythosiphon pisum (Harris) on Vicia fabaL., there were increases in the MRGR of the aphids feeding on fumigated plants as compared to clean air controls, both during and post fumigation. The increases in MRGR ranged from 6 to 75%, with the majority falling between 25 and 40%. A. pisum on V. faba showed a consistent negative response, with decreases in MRGR between -9 and -12%. The changes in aohid MRGR were not due to direct effects, as no significant differences in MRGR were observed between fumigated and clean air chambers when aphids were fed on artificial diet sachets during fumigation.     

Effects of SO2, NO2, and O3 on population development and morphological and physiological parameters of native herb layer species in a beech forest

The native ground vegetation of a beech forest was fumigated with moderate doses of SO(2), NO(2), and O(3) in open-top chambers. The effects of fumigants on growth and above-ground development were dependent on species. The treatments caused early senescence in several of the species present. The epicuticular waxes were attacked by fumigation, which was shown by higher wettability of the leaf surfaces and by leaching of ions. Interspecific differences were observed in the responses of transpiration and photosynthesis to fumigation. Similar patterns of effects on transpiration and photosynthesis, however, were found in the same species. Carbohydrate metabolism was altered by fumigation, leading to starch accumulation in the leaves. Besides effects on higher plants, fumigations also resulted in alterations of the soil microflora. The bacteria/fungi ratio was depressed at the fumigation plots.     

Variation in ozone sensitivity among clones of Betula pendula and Betula pubescens

Forty clones of Betula pendula and 6 clones of Betula pubescens, originating from southern and central Finland, were ranked in order of ozone sensitivity according to visible injuries, growth and leaf senescense under low ozone exposure. The plants were fumigated in natural climatic conditions using an open-air exposure system during two growing seasons. Control plants were grown under ambient air, and the elevated-ozone exposures were 1.6x the ambient in 1994 and 1.7x the ambient in 1995. The differences in ozone sensitivity among clones were large. Ozone tolerance was related to thicker leaves and higher stomatal density as compared to sensitive clones. Ultrastructural ozone-induced symptoms were found in chloroplasts of sensitive clones. Increased number of visibly injured leaves on fumigated plants was correlated with reduced leaf formation, foliage area, shoot dry wt and number of stomata, and increased yellowing of leaves. The results suggest that a considerable proportion of birch trees, showing high sensitivity to ozone, are at risk if ambient ozone exposures increase.     

Apolipophorin III and transmission electron microscopy as toxicity indicators for harmaline and tea saponin in Spodoptera exigua (Noctuidae: Lepidoptera)

Apolipophorin III, traditionally known for lipid transport in insects is fairly established as toxicity indicator against harmaline and tea saponin during this study. Apolipophorin III expressed in the hemolymph and midgut tissues of 3rd, 4th, 5th larval instars and pupae of Spodoptera exigua. Apolipophorin III presence was further confirmed by achieving its partial cDNA (Genbank accession no. FJ606822) of 448 bp. qRT PCR revealed that tea saponin resulted in significant reduction of gene expression in 3rd and 4th larval instars but increased in 5th instar as compared to control. Harmaline caused gradual increase of gene expression in 3rd, 4th and 5th instars after feeding on the treated diet. Fifth instar larvae synonymously resulted in the highest gene expressions against both the biochemicals. After the injection of harmaline and tea saponin abrupt increase in gene expression of 4th, 5th larval instar and pupae was observed as compared to control treatment. Transmission electron microscopy of midgut epithelium after being fed with harmaline and tea saponin depicted certain cytological changes. Harmaline treatment lead to cytoplasm vacuolization, mitochondrial disruption, spherocrystals with concentric layers, irregular nucleus and floating nuclei in cytoplasm. Tea saponin treatment resulted in denser cytoplasm, higher intracellular osmotic concentration and reduced complement of apical microvilli. Cells were found to have only a few mitochondria and glycogen deposits in comparison to control treatment.     

Persistent stimulation of CO2 assimilation and stomatal conductance by summer ozone fumigation in Norway spruce

CO(2) assimilation rate, stomatal conductance and chlorophyll content of current and previous years' needles of Norway spruce were measured in May 1988, 205 days after the cessation of ozone fumigation during the summer of 1987. Rates of assimilation were consistently higher for both needle year age classes for ozone fumigated trees in comparison to control trees, although only statistically significant for part of the day for current year's needles. A 26% and 48% stimulation, overall, in mean daily rates of assimilation for current and previous years' needles of ozone fumigated trees was observed. This was due to an enhanced apparent quantum yield and light saturated rate of assimilation of ozone fumigated trees. The temperature response regression of assimilation versus temperature was also greater, such that at any given temperature, assimilation was higher for ozone treated trees than control trees. Stomatal conductance was greater for ozone fumigated trees than the controls, but this was only marginally statistically significant. Moreover, there was a consistent increase in chlorophyll content in both year classes in ozone-treated trees. These results are discussed in relation to a possible long term effect of ozone fumigation upon the processes of conifer winter hardening and spring de-hardening.     

Impact of fungicides on active oxygen species and antioxidant enzymes in spring barley (Hordeum vulgare L.) exposed to ozone.

Two modern fungicides, a strobilurin, azoxystrobin (AZO), and a triazole, epoxiconazole (EPO), applied as foliar spray on spring barley (Hordeum vulgare L. cv. Scarlett) 3 days prior to fumigation with injurious doses of ozone (150-250 ppb; 5 days; 7 h/day) induced a 50-60% protection against ozone injury on leaves. Fungicide treatments of barley plants at growth stage (GS) 32 significantly increased the total leaf soluble protein content. Additionally, activities of the antioxidative enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate-peroxidase (APX) and glutathione reductase (GR) were increased by both fungicides at maximal rates of 16, 75, 51 and 144%, respectively. Guiacol-peroxidase (POX) activity was elevated by 50-110% only in AZO treated plants, while this effect was lacking after treatments with EPO. This coincided with elevated levels of hydrogen peroxide (H2O2) only in EPO and not in AZO treated plants. The enhancement of the plant antioxidative system by the two fungicides significantly and considerably reduced the level of superoxide (O2*-) in leaves. Fumigation of barley plants for 4 days with non-injurious ozone doses (120-150 ppb, 7 h/day) markedly and immediately stimulated O2*- accumulation in leaves, while H2O2 was increased only after the third day of fumigation. Therefore, O2*- itself or as precursor of even more toxic oxyradicals appears to be more indicative for ozone-induced leaf damage than H2O2. Ozone also induced significant increases in the activity of antioxidant enzymes (SOD, POX and CAT) after 2 days of fumigation in fungicide untreated plants, while after 4 days of fumigation these enzymes declined to a level lower than in unfumigated plants, due to the oxidative degradation of leaf proteins. This is the first report demonstrating the marked enhancement of plant antioxidative enzymes and the enhanced scavenging of potentially harmful O2*- by fungicides as a mechanism of protecting plants against noxious oxidative stress from the environment. The antioxidant effect of modern fungicides widely used in intense cereal production in many countries represents an important factor when evaluating potential air pollution effects in agriculture.     

Indirect effects of air pollutants: Changes in plant/parasite interactions

The impact of air pollutants on plant/parasite-interactions has been investigated. It could be demonstrated that fumigation of Vicia faba L. with 0.15 ppm SO2 (400 microg m(-3)) or 0.2 ppm NO2 (400 microg m(-3)) during 7 days caused changes in plant metabolism which resulted in higher growth rates of the aphid Aphis fabae Scop. feeding on these plants. Fumigation of V. faba with 0.085 ppm O3 during 2 or 3 days, however, caused decreased aphid growth on fumigated plants. That result could be reversed by higher O3 concentrations or through the presence of NOx during O3 fumigation. Ambient air comprising a mixture of pollutant gases had a strong enhancing effect on aphid performance. Thus, the growth of A. fabae on field bean plants was significantly higher in ambient summertime. London air than in charcoal-filtered air. Similarly, the growth of Macrosiphon rosae L. on rose bushes (Rosa sp., cv. Nina Weibull) was improved in ambient summertime Munich air; the increase in growth rate averaged about 20%.     

Effects of simultaneous ozone exposure and nitrogen loads on carbohydrate concentrations, biomass, growth, and nutrient concentrations of young beech trees (Fagus sylvatica)

Beech seedlings were grown under different nitrogen fertilisation regimes (0, 20, 40, and 80 kg Nha(-1)yr(-1)) for three years and were fumigated with either charcoal-filtered (F) or ambient air (O3). Nitrogen fertilisation increased leaf necroses, aphid infestations, and nutrient ratios in the leaves (N:P and N:K), as a result of decreased phosphorus and potassium concentrations. For plant growth, biomass accumulation, and starch concentrations, a positive nitrogen effect was found, but only for fertilisations of up to 40 kg Nha(-1) yr(-1). The highest nitrogen load, however, reduced leaf area, leaf water content, growth, biomass accumulation, and starch concentrations, whereas soluble carbohydrate concentrations were enhanced. The ozone fumigation resulted in reduced leaf area, leaf water content, shoot growth, root biomass accumulation, and decreased starch, phosphorus, and potassium concentrations, increasing the N:P and N:K ratios. A combined effect of the two pollutants was detected for the leaf area and the shoot elongation, where ozone fumigation amplified the nitrogen effects.     

The effect of reciprocal treatments with ozone and ultraviolet-B radiation on photosynthesis and growth of perennial grass Elymus athericus

The impact on plant growth of the simultaneously changing factors of the global climate, rising tropospheric O3 concentrations and increasing UV-B radiation fluxes, has been tested in a combined glasshouse and growth chamber experiment. The saltmarsh grass species Elymus athericus was sequentially fumigated for two weeks with O3 and for another two weeks irradiated with UV-B (vv). Exposure to elevated UV-B did not negatively affect photosynthesis or plant growth. Fumigation with O3 had a depressing effect on net photosynthesis, the number and biomass of flowers, the number of leaves and the number of shoots. O3-induced damage only was observed in plants which had been fumigated during the last two weeks of the experiment. Since interactive responses were not observed, results suggest different primary target sites for O3 and UV-B within the plant.     

Plant-mediated effects of heavy metal pollution on host choice of a grass miner

We studied the effects of heavy metal exposure on host plant choice and performance of the grass miner Chromatomyia milii (Diptera, Agromyzidae). Cadmium decreased plant growth in a dose-dependent way. C. milii preferred the control to the cadmium-exposed plants for feeding and oviposition. Moreover, preference for the control plants increased with increasing cadmium exposure of the alternative choice. Adult and offspring performance decreased with increasing plant cadmium exposure. This suggests that, at least under our laboratory conditions, host choice of C. milii is adaptive under pollution stress. Foliar cadmium concentration increased and the soluble sugar concentration decreased with increasing cadmium exposure. Regression analysis showed that both latter components might be responsible for the decrease in performance of C. milii on cadmium-exposed plants. The protein and amino acid concentration of the leaves, the amount of structural defenses, and water concentration were not affected by the cadmium treatment.     

Effects of simultaneous ozone exposure and nitrogen loads on carbohydrate concentrations, biomass, and growth of young spruce trees (Picea abies)

Spruce saplings were grown under different nitrogen fertilization regimes in eight chamberless fumigation systems, which were fumigated with either charcoal-filtered (F) or ambient air (O3). After the third growing season trees were harvested for biomass and non-structural carbohydrate analysis. Nitrogen had an overall positive effect on the investigated plant parameters, resulting in increased shoot elongation, biomass production, fine root soluble carbohydrate concentrations, and also slightly increased starch concentrations of stems and roots. Only needle starch concentrations and fine root sugar alcohol concentrations were decreased. Ozone fumigation resulted in needle discolorations and affected most parameters negatively, including decreased shoot elongation and decreased starch concentrations in roots, stems, and needles. In fine roots, however, soluble carbohydrate concentrations remained unaffected or increased by ozone fumigation. The only significant interaction was an antagonistic effect on root starch concentrations, where higher nitrogen levels alleviated the negative impact of ozone.     

The effects of ozone-exposed sugar maple seedlings on the biological performance and the feeding preference of the forest tent caterpillar (Malacosoma disstria Hbn.)

The effects of exposure of sugar maple (Acer saccharum Marsh.) to ozone on the entire larval stage of a native insect have not been previously investigated. This study reports the effects of sugar maple seedlings exposed to different ozone concentrations on the relative performance and the feeding preference of the forest tent caterpillar (Malacosoma disstria Hbn.). Three-year-old seedlings were set in nine open-top field chambers in the spring of 1992 and 1993. Three ozone concentrations were generated: charcoal-filtered ambient air (0x), ambient air (1x) and three times ambient air (3x). In 1992, female and male larval development time did not differ among ozone treatments. In 1993, female larvae reared on 3x developed faster than those on 0x and 1x, while male larvae were not affected. Ozone treatments did not influence pupal weights except for males in 1993 where pupae reared on 0x were heavier than 1x but did not differ from 3x. Larval and pupal survival rates were not affected by ozone in either year. Finally, 4th and 5th instar larvae showed a significant feeding preference for 3x foliage in 1993 but not in 1992. The response of the forest tent caterpillar to ozone exposed seedlings varied between years and could be more sensitive to annual climatic variations than ozone.     

Seasonal and diurnal gas exchange differences in ozone-sensitive common milkweed (Asclepias syriaca L.) in relation to ozone uptake

Stomatal conductance and net photosynthesis of common milkweed (Asclepias syriaca L.) plants in two different soil moisture regimes were directly quantified and subsequently modeled over an entire growing season. Direct measurements captured the dynamic response of stomatal conductance to changing environmental conditions throughout the day, as well as declining gas exchange and carbon assimilation throughout the growth period beyond an early summer maximum. This phenomenon was observed in plants grown both with and without supplemental soil moisture, the latter of which should theoretically mitigate against harmful physiological effects caused by exposure to ozone. Seasonally declining rates of stomatal conductance were found to be substantial and incorporated into models, making them less susceptible to the overestimations of effective exposure that are an inherent source of error in ozone exposure indices. The species-specific evidence presented here supports the integration of dynamic physiological processes into flux-based modeling approaches for the prediction of ozone injury in vegetation.     

Seasonal changes in the tissue-metal (Cd, Zn and Pb) concentrations in two ecophysiologically dissimilar earthworm species: pollution-monitoring implications

During two consecutive growing seasons, the same potted individuals of European aspen (Populus tremula), grown from root cuttings of one clone, were fumigated with either ambient air or ozone concentrations of 0 (control), 0.05 or 0.1 microlitre litre(-1). Structure and biomass of the annually formed branches were analysed after excision at the end of each season. Only at 0.1 microlitre litre(-1) was branch weight reduced, and crooked axes occurred in each season. During the second season, branch length and leaf sizes were strongly reduced, while many leaves displayed yellowish deficiency symptoms and lowered cation concentrations. Such leaves contrasted to those showing characteristic O3-bronzing. Although foliage density was enhanced due to reduced branch length, the area of attached foliage was limited by the small leaf sizes, necrotic leaves and premature leaf loss. During mid-summer of the second fumigation period, photosynthetic capacity, carboxylation efficiency and water-use efficiency (WUE) declined in (attached) yellowish and bronze leaves at 0.1 microlitre litre(-1), whereas green leaves at 0.05 microlitre litre(-1) displayed accelerated senescence in late summer while maintaining WUE. It is concluded that the differences in branch growth between the two growing seasons were caused in part by internal changes in those plant organs (root and basal stem), which had experienced both fumigation periods.