Growth response to ozone of annual species from Mediterranean pastures

Ozone (O3) phytotoxicity has been reported on a wide range of plant species. However, scarce information has been provided regarding the sensitivity of semi-natural grassland species, especially those from dehesa Mediterranean grasslands, in spite of their great biological diversity and the high O3 levels recorded in the region. A screening study was carried out in open-top chambers (OTCs) to assess the O3-sensitivity of representative therophytes of these ecosystems based on the response of selected growth-related parameters. Three O3 treatments and 3 OTCs per treatment were used. Legume species were very sensitive to O3, because 78% of the tested species showed detrimental effects on their total biomass relative growth rate (RGR) following their exposure to O3. The Trifolium genus was particularly sensitive showing O3-induced adverse effects on most of the assessed parameters. Gramineae plants were less sensitive than Leguminosae species because detrimental effects on total biomass RGR were only observed in 14% of the assessed species. No relationship was found between relative growth rates when growing in clean air and O3 susceptibility. The implications of these effects on the performance of dehesa acidic grasslands and on the definition of ozone critical levels for the protection of semi-natural vegetation are discussed.     

Modelling annual pasture dynamics: Application to stomatal ozone deposition

Modelling ozone (O₃) deposition for impact risk assessment is still poorly developed for herbaceous vegetation, particularly for Mediterranean annual pastures. High inter-annual climatic variability in the Mediterranean area makes it difficult to develop models characterizing gas exchange behaviour and air pollutant absorption suitable for risk assessment. This paper presents a new model to estimate stomatal conductance (g_s) of Trifolium subterraneum, a characteristic species of dehesa pastures. The MEDPAS (MEDiterranean PAStures) model couples 3 modules estimating soil water content (SWC), vegetation growth and g_s. The g_s module is a reparameterized version of the stomatal component of the EMEP DO₃SE O₃ deposition model. The MEDPAS model was applied to two contrasting years representing typical dry and humid springs respectively and with different O₃ exposures. The MEDPAS model reproduced realistically the g_s seasonal and inter-annual variations observed in the field. SWC was identified as the major driver of differences across years. Despite the higher O₃ exposure in the dry year, meteorological conditions favoured 2.1 times higher g_s and 56 day longer growing season in the humid year compared to the dry year. This resulted in higher ozone fluxes absorbed by T. subterraneum in the humid year. High inter-family variability was found in gas exchange rates, therefore limiting the relevance of single species O₃ deposition flux modelling for dehesa pastures. Stomatal conductance dynamics at the canopy level need to be considered for more accurate O₃ flux modelling for present and future climate scenarios in the Mediterranean area.     

Growth and physiology of Northern Red Oak: preliminary comparisons of mature tree and seedling responses to ozone

Considerable progress has been made during the past decade in the development of mechanistic models that allow complex chemical, physical, and biological processes to be evaluated in the global change context. However, quantitative predictions of the response of individual trees, stands, and forest ecosystems to pollutants and climatic variables require extrapolation of existing data sets, derived largely from seedling studies, to increasing levels of complexity with little or no understanding of the uncertainties associated with these extrapolations. Consequently, a project designed to address concerns associated with scaling from seedling to mature tree responses was initiated. During the 1990 and 1991 growing seasons, mature northern red oak (Quercus rubra L.) trees and seedlings were exposed to subambient, ambient, and twice ambient ozone (O(3)) concentrations. The initial focus of the study was to identify possible trends and obvious differences between mature trees and seedlings, both in terms of growth and physiology and in response to O(3). Generally, mature trees exhibited a greater decrease in photosynthesis rates over the growing season than did the seedlings. Ozone treatments had no consistent effect on gas exchange rates of seedlings, but the twice ambient O(3) treatment resulted in reduced photosynthesis rates in the mature tree. Despite no effect of O(3) on seedling gas exchange rates, total seedling biomass was significantly less at the end of the 1991 growing season for those seedlings exposed to twice ambient O(3) levels. Disproportionate reductions in root biomass also resulted in reduced root to shoot ratios at elevated O(3) concentrations.     

Foliar injury, leaf gas exchange and biomass responses of black cherry (Prunus serotina Ehrh.) half-sibling families to ozone exposure

Open pollinated families of black cherry seedlings were studied to determine genotypic differences in foliar ozone injury and leaf gas exchange in 1994 and growth response following three growing seasons. An O(3)-sensitive half-sibling family (R-12) and an O(3)-tolerant half-sibling family (MO-7) planted in natural soil were studied along with generic nursery stock (NS) seedlings. Ozone exposure treatments were provided through open top chambers and consisted of 50, 75, and 97% of ambient ozone, and open plots from May 9 to August 26, 1994. Ambient ozone concentrations reached an hourly peak of 88 ppb with 7-hour averages ranging from 39 to 46 ppb. Seedlings in the 50 and 75% of ambient chambers were never exposed to greater than 80 ppb O(3). Visible foliar ozone injury (stipple) was significantly higher for R-12 seedlings than MO-7 seedlings and increased with increasing ozone exposures. For the chamber treatments averaged over all families, there was no significant difference in stomatal conductance and net photosynthetic rates, but there was a significant decrease in root biomass, and a significant decrease in root/shoot ratio between the 50 and 97% of ambient chambers. Stomatal conductance and net photosynthetic rates were significantly different between families with R-12 seedlings generally greater than MO-7 seedlings. The R-12 seedlings had a 7.5 mmol m(-2) increase in ozone uptake compared to MO-7, and at the same cumulative O(3) exposure R-12 exhibited 40.9% stippled leaf area, whereas MO-7 had 9.2% stippled leaf area. Significant differences were observed in stem volume growth and total final biomass between the open-top chambers and open plots. Although R-12 had the most severe foliar ozone injury, this family had significantly greater stem volume growth and total final biomass than MO-7 and NS seedlings. Root:shoot ratio was not significantly different between MO-7 and R-12 seedlings.     

Physiological and foliar injury responses of Prunus serotina,Fraxinus americana,and Acer rubrum seedlings to varying soil moisture and ozone

Sixteen black cherry (Prunus serotina, Ehrh.), 10 white ash (Fraxinus americana, L.) and 10 red maple (Acer rubrum, L.) 1-year old seedlings were planted per plot in 1997 on a former nursery bed within 12 open-top chambers and six open plots. Seedlings were exposed to three different ozone scenarios (ambient air: 100% O3; non-filtered air: 98% ambient O3; charcoal-filtered air: 50% ambient O3) within each of two different water regimes (nine plots irrigated, nine plots non-irrigated) during three growing seasons.During the 1998 and 1999 growing season, leaf gas exchange, plant water relations, and foliar injury were measured. Climatic data,ambient- and chamber-ozone-concentrations were monitored. We found that seedlings grown under irrigated conditions had similar (in 1998) but significantly higher gas exchange rates (in 1999) than seedlings grown within non-irrigated plots among similar ozone exposures. Cherry and ash had similar ozone uptake but cherry developed more ozone-induced injury (< 34% affected leaf area, LAA) than ash (<5% LAA), while maple rarely showed foliar injury, indicating the species differed in ozone sensitivity. Significantly more severe injury on seedlings grown under irrigated conditions than seedlings grown under non-irrigated conditions demonstrated that soil moisture altered seedling responses to ambient ozone exposures.     

Effects of ozone impact on the gas exchange and chlorophyll fluorescence of juvenile birch stems (Betula pendula Roth.)

Effects of ozone impact on gas exchange and chlorophyll fluorescence of juvenile birch (Betula pendula) stems and leaves were investigated. Significant differences in the response of leaves and stems to ozone were found. In leaves, O3 exposure led to a significant decline in photosynthetic rates, whereas stems revealed an increased dark respiration and a concomitant increase in corticular photosynthesis. In contrast to birch leaves, corticular photosynthesis appeared to support the carbon balance of stems or even of the whole-tree under O3 stress. The differences in the ozone-response between leaves and stems were found to be related to ozone uptake rates, and thus to inherent differences in leaf and stem O3 conductance.     

Influence of ozone stress on growth processes, yields and grain quality characteristics among soybean cultivars

Field studies were conducted at USDA Beltsville Agricultural Research Center, Beltsville, Maryland, in 1984 and 1985 using open-top chambers to acquire information on the responses of 12 soybean (Glycine max L. Merr.) cultivars to O3 stress and to examine the interactions between maturity groups and O3 stress. Cultivars representing Groups III, IV, and V were exposed for approximately 3 months to charcoal-filtered air (CF) and nonfiltered air plus 40 nl litre(-1) O3 (NF + O3). Ozone was added 6 h d(-1), 5 d week(-1) for 13 weeks. The CF effectively reduced the accumulative oxidant exposure (AOX) to less than 1.0 microl litre(-1) h and the NF + O3 treatment approximately doubled the ambient AOX (16.7 microl litre(-1) h) to about 30 microl litre(-1) h. The AOX estimates the total O3 exposure above 30 nl litre(-1) during an entire growing season. Plant growth rates and relative growth rates were reduced by 17.0 and 14.4%, respectively, when averaged over cultivars. Based on growth rates, the Group III cultivars were the most affected by O3 stress. Averaged over cultivars, leaf expansion rates, leaf conductance, and transpiration rates were lower in the NF + O3 treatment compared to the CF control; however, wide variation was found with the stomatal results from field observations. Combined over years and cultivars, grain yield was reduced by an average of 12.5% by O3 stress with 3 of 12 cultivars showing significant reductions. Grain protein content was increased by 0.7% by O3 stress, but cultivar differences were equal to the differences caused by the O3 treatments. Grain oil content was unchanged by the O3 treatments. Group IV cultivars showed the greatest decrease in grain yield due to O3 stress. Multiple regression analyses were calculated using the difference between the CF and NF + O3 treatment as a measure of O3 stress. Significant positive relationships were found among net assimilation rates, plant growth rates, relative growth rates, and leaf expansion rates, which suggest that growth analysis characteristics would be useful in addition to yield in air pollution tolerance improvement studies with soybeans.     

Response patterns in adult forest trees to chronic ozone stress: identification of variations and consistencies

The responsiveness of adult beech and spruce trees to chronic O(3) stress was studied at a free-air O(3) exposure experiment in Freising/Germany. Over three growing seasons, gas exchange characteristics, biochemical parameters, macroscopic O(3) injury and the phenology of leaf organs were investigated, along with assessments of branch and stem growth as indications of tree performance. To assess response pattern to chronic O(3) stress in adult forest trees, we introduce a new evaluation approach, which provides a comprehensive, readily accomplishable overview across several tree-internal scaling levels, different canopy regions and growing seasons. This new approach, based on a three-grade colour coding, combines statistical analysis and the proficient ability of the "human eye" in pattern recognition.     

Effects of ozone on the foliar histology of the mastic plant (Pistacia lentiscus L.)

An open-top chamber study was conducted to investigate the tissue and cellular-level foliar effects of ozone (O3) on a Mediterranean evergreen species, the mastic plant (Pistacia lentiscus L.). Plants were exposed at three different O3 levels, and leaf samples were collected periodically from the beginning of the exposure. Although no visible foliar injury was evident, alterations of the plastids and vacuoles in the mesophyll were observed. Senescence processes were accelerated with an anomalous stacking of tannin vacuoles, and a reduction in the size and number of the chloroplasts. Overall, most of the modifications induced by O3 were consistent with previously reported observations on deciduous broadleaf species, with the exception of alterations in the cells covering the secretory channels, reported here as a new finding. Comments on the feasibility of using microscopy to validate O3 related field observations and subtle foliar injury are also given.     

Physiological and foliar symptom response in the crowns of Prunus serotina, Fraxinus americana and Acer rubrum canopy trees to ambient ozone under forest conditions

The crowns of five canopy dominant black cherry (Prunus serotina Ehrh.), five white ash (Fraxinus americana L.), and six red maple (Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0-5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake (U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential (psi(L)) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor (g(wv)) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity (P(n)), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions (P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between g(wv) and P(n) demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.     

Effects of long-term ozone fumigations on growth and gas exchange of Fraser fir seedlings

Fraser fir seedlings from two seed sources in the Southern Appalachians (Mt Mitchell, North Carolina, a declining population; and Mt Rogers, Virginia, a relatively healthy population) were subjected to long-term (2.5 years) intermittent ozone fumigations (0.025, 0.070, and 0.150 ppm) while being grown through five growth cycles in an accelerated-growing regime. Fumigations took place during bud break, stem elongation and bud set. Following each growing cycle, gas exchange parameters and dry weights were determined. The ozone fumigations did not produce any effect on seedling growth. The ozone fumigation effects on gas exchange parameters were inconsistent, and generally not statistically different, with no differences occurring between seed sources. There was no correlation between photosynthetic rates and seedling growth. These results provide no evidence that ozone may be contributing to the differences in decline noted between the Mt Rogers and Mt Mitchell populations of Fraser fir.     

White clover clones as a cost-effective indicator of phytotoxic ozone: 10 years of experience from central Italy

Data collected at one site in central Italy using the NC-S/NC-R clover (Trifolium repens) biotype system during 1997-2007 were analysed in order to assess: (a) its performance under Mediterranean conditions; (b) variations of ozone damage linked with meteorological conditions; (c) if critical level approach is a good predictor of ozone risk on vegetation. NC-S dry biomasses were systematically lower than those of NC-R, the mean ratio being 0.7. Relevant relationship between ozone visible injury and cumulated values of AOT40 were also reported. Temperature and number of rainy days were the most important factors associated with ozone presence and, as a consequence, with leaf injury index. Photosynthetic gas exchange properties indicate that NC-S has higher values of stomatal conductance.     

Tree age dependence and within-canopy variation of leaf gas exchange and antioxidative defence in Fagus sylvatica under experimental free-air ozone exposure

We characterized leaf gas exchange and antioxidative defence of two-year-old seedlings and 60-year-old trees of Fagus sylvatica exposed to ambient (1 x O3) or two-fold ambient (2 x O3) O3 concentrations (maximum of 150 ppb) in a free-air canopy exposure system throughout the growing season. Decline in photosynthesis from sun-exposed to shaded conditions was more pronounced in adult than juvenile trees. Seedling leaves and leaves in the sun-exposed canopy had higher stomatal conductance and higher internal CO2 concentrations relative to leaves of adult trees and leaves in shaded conditions. There was a weak overall depression of photosynthesis in the 2 x O3 variants across age classes and canopy positions. Pigment and tocopherol concentrations of leaves were significantly affected by canopy position and tree age, whereas differences between 1 x O3 and 2 x O3 regimes were not observed. Glutathione concentrations were significantly increased under 2 x O3 across both age classes and canopy levels. Seedlings differed from adult trees in relevant physiological and biochemical traits in ozone response. The water-soluble antioxidative systems responded most sensitively to 2 x O3 without regard of tree age or canopy position.     

Crop growth along a gradient of ambient air pollution

An experiment, designed to elucidate the relative importance of SO2, NO2, O3, and other environmental factors in influencing the performance of four cultivars of Trifolium pratense L. and Hordeum vulgare L., was performed by growing plants in situ along a transect from central London into the surrounding countryside. A multiple regression analysis provided evidence of significant effects of SO2, NO2, and, to a lesser extent, O3, on vegetative and reproductive growth parameters, although these differed according to pollutant, cultivar, species, and the parameter concerned. The significance of these findings for the impact of ambient air pollution on the growth of crops in the more polluted rural areas of western Europe is suggested by the fact that mean SO2, NO2, and O3 concentrations in the experimental area are less than 0.020 (39.2 microg/m3), 0.025 (47.75 microg/m3), and 0.030 ppm (58.8 microg/m3), respectively. The value of the technique is discussed with respect to other studies on the effects of low levels of air pollution on crops.     

Effects of ozone on managed pasture: II. Yield, species composition, canopy structure, and forage quality

Managed pasture composed of grasses, clover and weeds was exposed in open-top chambers to different levels of ozone (O(3)) during two consecutive seasons to study changes in yield, species composition, canopy structure, and forage quality. The pasture was established in 1990 and exposed in 1991 and 1992. Ozone treatments included charcoal-filtered air (CF), non-filtered air (NF), and two treatments with O(3) added to NF air during periods with global radiation >/= 400 W m(-2) (NF(+), NF(++)). The ratio between the 2-year cumulative, radiation-weighted O(3) concentration in ambient air (= 365 microl litre(-1) h) and in the different treatments was 0.50 (CF), 0.85 (NF), 1.11 (NF(+)), and 1.64 (NF(++)). Plots were harvested four times in 1991, and five times in 1992. The total forage yield for both seasons was modified little by O(3). The yield reduction in NF(++) was only 10% as compared to the CF treatment. Also, only marginal changes were observed in forage quality (Ca, crude protein, crude fibre), and in leaf area index and fractional light penetration. Ozone strongly reduced the yield of clover (Trifolium repens L. and Trifolium pratense L.). The O(3)-effect on clover growth was small after the first harvest and increased with each growth period. In NF, the 2-year cumulative clover yield was reduced by 24% relative to CF. In NF(++), clover growth almost ceased near the end of the second season. The reduction in clover yield with increasing O(3) was associated with a slight increase in the yield of grasses (mainly Dacytlis glomerata L). The increase in the proportion of invading species (weeds or herbs) (Taraxacum officinale L.) during the experiment was not significantly affected by O(3). A second order polynomial function was fitted to the data to establish an exposure-response model for the cumulative clover yield and the cumulative, radiation-weighted O(3) dose, and linear models were developed for total forage mass, grass yield and yield of weeds. Reducing O(3) from elevated levels (NF(+) and NF(++)) during the first season to near-ambient levels (NF) during the second season resulted in a significant recovery of clover yield after two re-growth periods. It is concluded that continuous exposure to ambient levels of O(3) negatively affects the yield of clover in frequently cut, managed pasture, but because of the relatively small proportion of clover, the shift in species composition only marginally affects total forage yield and forage quality. It is emphasised, however, that limitations of the experimental system must be taken into account before extrapolations to real field situations can be made.     

Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow-poplar seedlings

Potted seedlings of black cherry (Prunus serotina Ehrh.) (BC), green ash (Fraxinus pennsylvanica Marsh.) (GA), and yellow-poplar (Liriodendron tulipifera L.) (YP) were exposed to one of the four treatments: (1) charcoal-filtered air (CF) at ambient CO(2) (control); (2) twice ambient O(3) (2 x O(3)); (3) twice ambient CO(2) (650 microl l(-1)) plus CF air (2 x CO(2)); or (4) twice ambient CO(2) (650 microl l(-1)) plus twice ambient O(3) (2 x CO(2) + 2 x O(3)). The treatments were duplicated in eight continuously stirred tank reactors for 10 weeks. Gas exchange was measured during the last 3 weeks of treatment and all seedlings were destructively harvested after 10 weeks. Significant interactive effects of O(3) and CO(2) on the gas exchange of all three species were limited. The effects of elevated CO(2) and O(3), singly and combined, on light-saturated net photosynthesis (A(max)) and stomatal conductance (g(s)) were inconsistent across species. In all three species, elevated O(3) had no effect on g(s). Elevated CO(2) significantly increased A(max) in GA and YP foliage, and decreased g(s) in YP foliage. Maximum carbon exchange rates and quantum efficiencies derived from light-response curves increased, while compensation irradiance and dark respiration decreased in all three species when exposed to 2 x CO(2). Elevated O(3) affected few of these parameters but any change that was observed was opposite to that from exposure to 2 x CO(2)-air. Interactive effects of CO(2) and O(3) on light-response parameters were limited. Carboxylation efficiencies, derived from CO(2)-response curves (A/C(i) curves) decreased only in YP foliage exposed to 2 x CO(2)-air. In general, growth was significantly stimulated by 2 x CO(2) in all three species; though there were few significant growth responses following exposure to 2 x O(3) or the combination of 2 x CO(2) plus 2 x O(3). Results indicate that responses to interacting stressors such as O(3) and CO(2) are species specific.     

The effects of crude oil and the effectiveness of cleaner application following oiling on US Gulf of Mexico coastal marsh plants

Field studies were conducted in two different marsh habitats in Louisiana coastal wetlands to evaluate the effects of oiling (using South Louisiana Crude oil, SLC) and the effectiveness of a shoreline cleaner (COREXIT 9580) in removing oil from plant canopies. The study sites represented two major marsh habitats; the brackish marsh site was covered by Spartina patens and the freshwater marsh was covered by Sagittaria lancifolia. Field studies were conducted in each habitat using replicated 5.8 m2 plots that were subjected to three treatments; oiled only, oiled + cleaner (cleaner was used 2 days after oiling), and a control. Plant gas exchange responses, survival, growth, and biomass accumulation were measured. Results indicated that oiling led to rapid reductions in leaf gas exchange rates in both species. However, both species in 'oiled + cleaned' plots displayed improved leaf conductance and CO2 fixation rates. Twelve weeks after treatment initiation, photosynthetic carbon fixation in both species had recovered to normal levels. Over the short-term, S. patens showed more sensitivity to oiling with SLC than S. lancifolia as was evident from the data of the number of live shoots and above-ground biomass. Above-ground biomass remained significantly lower than control in S. patens under 'oiled' and 'oiled + cleaned' treatments while it was comparable to controls in S. lancifolia. These studies indicated that the cleaner removed oil from marsh grasses and alleviated the short-term impact of oil on gas exchange function of the study plants. However, use of cleaner had no detectable effects on above-ground biomass production or regeneration at the end of the first growing season in S. patens. Similarly, no beneficial effects of cleaner on carbon fixation and number of live shoots were apparent beyond 12 weeks in S. lancifolia.     

Impact of biochar application to a Mediterranean wheat crop on soil microbial activity and greenhouse gas fluxes

Biochar has been recently proposed as a management strategy to improve crop productivity and global warming mitigation. However, the effect of such approach on soil greenhouse gas fluxes is highly uncertain and few data from field experiments are available. In a field trial, cultivated with wheat, biochar was added to the soil (3 or 6 kg m⁻²) in two growing seasons (2008/2009 and 2009/2010) so to monitor the effect of treatments on microbial parameters 3 months and 14 months after char addition. N₂O, CH₄ and CO₂ fluxes were measured in the field during the first year after char addition. Biochar incorporation into the soil increased soil pH (from 5.2 to 6.7) and the rates of net N mineralization, soil microbial respiration and denitrification activity in the first 3 months, but after 14 months treated and control plots did not differ significantly. No changes in total microbial biomass and net nitrification rate were observed. In char treated plots, soil N₂O fluxes were from 26% to 79% lower than N₂O fluxes in control plots, excluding four sampling dates after the last fertilization with urea, when N₂O emissions were higher in char treated plots. However, due to the high spatial variability, the observed differences were rarely significant. No significant differences of CH₄ fluxes and field soil respiration were observed among different treatments, with just few exceptions. Overall the char treatments showed a minimal impact on microbial parameters and GHG fluxes over the first 14 months after biochar incorporation.     

Comparison of calculated and measured foliar O3 flux in crop and forest species

We designed a new gas exchange system that concurrently measures foliar H2O, O3, and CO2 flux (HOC flux system) while delivering known O3 concentrations. Stomatal responses of three species were tested: snapbean, and seedlings of California black oak (deciduous broadleaf) and blue oak (evergreen broadleaf). Acute O3 exposure (120-250 ppb over an hour) was applied under moderate light and low vapor pressure deficits during near steady state conditions. The rate of stomatal closure was measured when the whole plant was placed in the dark. An adjacent leaf on each plant was also concurrently measured in an O3-free cuvette. Under some conditions, direct measurements and calculated foliar O3 flux were within the same order of magnitude; however, endogenously low gs or O3 exposure-induced depression of gs resulted in an overestimation of calculated O3 fluxes compared with measured O3 fluxes. Sluggish stomata in response to light extinction with concurrent O3 exposure, and incomplete stomatal closure likewise underestimated measured O3 flux.     

Emissions of isoprene,monoterpene and short-chained carbonyl compounds from Eucalyptus spp. in southern Australia

Eucalypts are among the highest emitters of biogenic volatile organic compounds, yet there is relatively little data available from field studies of this genus. Emissions of isoprene, monoterpenes and the short-chained carbonyls formaldehyde, acetaldehyde and acetone were determined from four species (Eucalyptus camaldulensis, Eucalyptus globulus, Eucalyptus grandis, and Eucalytpus viminalis) in Australia. A smaller comparative study was conducted on E. camaldulensis in south-eastern Australia. Carbonyl emissions, reported here for the first time from eucalypts, were generally comparable with rates reported for other species, with diurnal emissions peaking at about 4, 75 and 34 nmol m^?2 min^?1 for acetone, formaldehyde and acetaldehyde respectively. There was wide variation in diurnal isoprene and monoterpene emissions between species, but under standard conditions, isoprene emissions were much lower than previous reports. Conversely, standard emission rates of monoterpenes were as much as six times greater than previous reports for some species. Emission of each carbonyl was correlated with its ambient concentration across different species, but more weakly related to temperature. Acetaldehyde emission in particular was significantly correlated with transpiration, but not with sap flow or with ethanol concentrations in xylem sap, suggesting fermentation within the leaf and stomatal conductance are primary controlling processes. Differences in acetaldehyde exchange velocities between sites, in addition to transpiration differences, suggest stomata may indeed exert long term emission regulation, in contrast to compounds for which no biological sink exists.