Ozone In Open-top Chambers Research Articles

Determinants of stomatal sluggishness in ozone-exposed deciduous tree species

Our knowledge of ozone effects on dynamic stomatal response is still limited, especially in Asian tree species. We thus examined ozone effects on steady-state leaf gas exchange and stomatal dynamics in three common tree species of China (Ailanthus altissima, Fraxinus chinensis and Platanus orientalis). Seedlings were grown and were exposed to three levels of ozone in open-top chambers (42, 69, 100nmolmol−1 daylight average, from 09:00 to 18:00). At steady-state, ozone exposure induced an uncoupling of photosynthesis and stomatal conductance, as the former decreased while the latter did not. Dynamic stomatal response was investigated by cutting the leaf petiole after a steady-state stomatal conductance was reached. Ozone exposure increased stomatal sluggishness, i.e., slowed stomatal response after leaf cutting, in the following order of sensitivity, F. chinensis>A. altissima>P. orientalis. A restriction of stomatal ozone flux reduced the ozone-induced sluggishness in P. orientalis. The ozone-induced impairment of stomatal control was better explained by stomatal ozone flux per net photosynthesis rather than by stomatal ozone flux only. This suggests that ozone injury to stomatal control depends both on the amount of ozone entering a leaf and on the capacity for biochemical detoxification or repair. Leaf mass per area and the density of stomata did not affect stomatal sluggishness.

Do elevated ozone and variable light alter carbon transport to roots in sugar maple?

Summary • Here we conducted a series of 14C pulse-chase labeling experiments to test the hypothesis that ozone reduces allocation of recently assimilated carbon to roots of sugar maple (Acer saccharum). • Sugar maple seedlings were fumigated with 1.0 ×, 1.7 × and 3.0 × ambient ozone in open-top chambers for 3 yr under low and high light. Shoots were labeled with 14CO2 for 1 h in August of year 3, and seedlings were harvested 0, 4, 24 and 48 h after labeling. • Three years of ozone fumigation reduced total biomass of seedlings in low and high light treatments by 49% and 34%, respectively, and reduced per cent allocation of total seedling biomass to roots. Ozone similarly reduced allocation of net 14C (gross 14CO2 assimilated at time = 0 minus respiratory losses) to roots after 48 h, but not gross 14C, despite significant ozone effects on 14CO2 assimilation, leaf-level partitioning, and retention of gross carbon in shoots. • Although ozone delayed transport of 14C out of leaves initially, it had no effect on the transport process per se. Any reduction in net allocation to roots is most likely a function of changes in whole-plant source–sink relationships, with control a function of both shoot and root traits.

Impact of ozone on the growth of birch ( Betula pendula) saplings

Saplings of one half-sib family of birch, Betula pendula, were exposed to three levels of ozone in open-top chambers (OTCs) during two growing seasons 1997–1998. The ozone treatments were non-filtered air (NF, accumulated daylight AOT40 over the two growing seasons of 3.0 μl l −1 h), non-filtered air with extra ozone (NF+, accumulated daylight AOT40 of 27.3 μl l −1 h) and non-filtered air with additional extra ozone (NF++, accumulated daylight AOT40 of 120 μl l −1 h). The birch saplings, including the roots, were harvested after the first and second growing seasons. After the first growing season, the NF++ treatment reduced the total wood biomass by 22%, relative to the NF treatment. There was no further reduction of the total wood biomass in the NF++ treatment after the second growing season. The root biomass was reduced by 30% after the first growing season. The shoot/root ratio, as well as the proportional biomass of leaves, were increased by ozone during both years. The ozone impact on the relative growth rate was estimated to −2% per 10 μl l −1 h daylight AOT40 per growing season.

Seedling insensitivity to ozone for three conifer species native to Great Smoky Mountains National Park

Field symptoms typical of ozone injury have been observed on several conifer species in Great Smoky Mountains National Park, and tropospheric ozone levels in the Park can be high, suggesting that ozone may be causing growth impairment of these plants. The objective of this research was to test the ozone sensitivity of selected conifer species under controlled exposure conditions. Seedlings of three species of conifers, Table Mountain pine ( Pinus pungens), Virginia pine ( Pinus virginiana), and eastern hemlock ( Tsuga canadensis), were exposed to various levels of ozone in open-top chambers for one to three seasons in Great Smoky Mountains National Park in Tennessee, USA. A combination of episodic profiles (1988) and modified ambient exposure regimes (1989–92) were used. Episodic profiles simulated an average 7-day period from a monitoring station in the Park. Treatments used in 1988 were: charcoal-filtered (CF), 1.0× ambient, 2.0× ambient, and ambient air–no chamber (AA). In 1989 a 1.5× ambient treatment was added, and in 1990, additional chambers were made available, allowing a 0.5× ambient treatment to be added. Height, diameter, and foliar injury were measured most years. Exposures were 3 years for Table Mountain pine (1988–90), 3 years for hemlock (1989–91), and 1 and 2 years for three different sets of Virginia pine (1990, 1990–91, and 1992). There were no significant ( p<0.05) effects of ozone on any biomass fraction for any of the species, except for older needles in Table Mountain and Virginia pine, which decreased with ozone exposure. There were also no changes in biomass allocation patterns among species due to ozone exposure, except for Virginia pine in 1990, which showed an increase in the root:shoot ratio. There was foliar injury (chlorotic mottling) in the higher two treatments (1.0× and 2.0× for Table Mountain and 2.0× for Virginia pine), but high plant-to-plant variability obscured formal statistical significance in many cases. We conclude, at least for growth in the short-term, that seedlings of these three conifer species are insensitive to ambient and elevated levels of ozone, and that current levels of ozone in the Park are probably having minimal impacts on these particular species.

Use of a single-tree simulation model to predict effects of ozone and drought on growth of a white fir tree.

A physiologically based, single-tree simulation model, TREGRO, was parameterized with existing phenological, allometric, and growth data and used to predict effects of ozone and drought on growth of a 53-year-old white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.) tree following a 3-year model simulation. Multiple experimental simulations were conducted to assess the individual and interactive effects of ozone (O(3)) exposure and drought on growth of white fir. The effects of O(3) were imposed as reductions in carbon (C) assimilation of 0, 2.5, 5, 10, and 20%. Drought was imposed as 0, 10, 25, and 50% reductions in total annual precipitation. The results of the simulations were compared with the effects of O(3) on white fir seedlings grown in the presence and absence of ozone in open-top chambers and with a field survey of white fir trees subjected to a gradient of O(3). In the O(3) simulations, an O(3)-induced reduction in C assimilation of 2.5% reduced total tree biomass and branch total nonstructural carbohydrate (TNC) content by < 7%. Although quantifiable in simulation experiments, such small reductions would probably not be detectable in the field. Results from both an open-top chamber experiment and a field survey indicated that reductions in C assimilation of white fir growing in elevated O(3) were much greater than 2.5%, but were not statistically different from control values. A simulated O(3) reduction in C assimilation of >/= 10% reduced total tree biomass by 7% and branch TNC by 55%. Results from the field survey indicated that branch elongation was reduced in response to increased O(3) concentration, corroborating the simulated response of reduced C allocation to the branches of white fir. Although simulated reductions in total annual precipitation of >/= 25% reduced final tree biomass, the simulated reductions also reduced O(3) uptake and therefore reduced the O(3) response of white fir. However, a combination of low amounts of O(3) (2.5% reduction in C assimilation) and drought (25% reduction in annual precipitation) synergistically reduced C gain of white fir more than either stress individually. Our simulations predict that moderate drought (no more than a 25% reduction in total annual precipitation) may not ameliorate the response of white fir to O(3) and that moderate amounts of atmospheric O(3) and drought could be more detrimental to white fir than either stress singly.

Abscisic acid in needles of Pinus cembra in relation to ozone exposure.

Ozone pollution was analyzed in arolla pine (Pinus cembra L.) forests growing over two mountain ranges located in southern France by using specific ozone-sensitive tobacco plants as bio-indicators and a physico-chemical analyzer. Concentrations of abscisic acid (ABA) were determined in needles of healthy and declining trees in a massif with a declining forest and in a massif with a healthier forest. In addition, ABA was quantified in needles of trees exposed to either charcoal-filtered air or unfiltered air supplemented with ozone in open-top chambers located at the Col du Donon. The concentration of ABA in needles of injured trees increased when the trees were exposed to ozone either under field conditions or in open-top chambers; however, the difference in ABA concentration between control and ozone-exposed needles was less in the open-top chambers, where ozone was the sole variable, than in the field. The results are discussed in the context of the effects of ozone on plant water relations and hormone-mediated cell defense.

Accumulation of a porin‐like mRNA and a metallothionein‐like mRNA in various clones of Norway spruce upon long‐term treatment with ozone

SummaryIn a long‐term study six Norway spruce (Picea abies) clones from two different provenance regions were exposed to 150/μg/m3 and 300μg/m3 ozone in open top chambers. Differential screening of subtractive cDNA libraries made from mRNA of ozone‐treated trees identified several cDNA clones of ozone‐responsive genes, two of which were studied in more detail. One cDNA clone corresponded to a porin‐like mRNA, the other to a metallothionein‐like mRNA. Under moderate ozone exposure the accumulation of these two mRNAs was already detectable before damage symptoms became visible. The spruce clones varied in the level of accumulation for the mRNAs. This is discussed under the aspect of ozone‐induced early senescence rather than a defense reaction suppressing symptoms, because the two phenotypically most ozone‐‘tolerant’ spruce clones showed the lowest levels of accumulation for both mRNAs.

Influence of ozone and soil nitrogen content on the stem anatomy of Norway spruce saplings grown in open-top chambers

Four-year-old Norway spruce saplings ( Picea abies) were exposed to different concentrations of ozone in open-top chambers for 22 weeks. The treatments were charcoal filtered air (CF), non-filtered ambient air (NF) and two elevated ozone treatments: non-filtered air with O 3 added at 25 nl l −1 (NF25) and at 50 nl l −1 (NF50). In each chamber, half of the investigated saplings were grown on nitrogen-poor soil (17 mg N kg −1) and half on nitrogen-enriched soil (34 mg N kg −1). Changes in the anatomy of the stem, the growth parameters, and nitrogen concentration in needles and stem were followed over one growing season. In saplings grown on nitrogen-enriched soil the number of tracheids and the number of latewood tracheids decreased, but diameter of latewood tracheids increased with increasing ozone concentration in comparison to ambient level of ozone. In the fumigated saplings grown on nitrogen-poor soil, the number of sieve cells and diameter of latewood tracheids decreased with increasing ozone concentration in comparison to ambient level of ozone. Ozone increased the thickness of sieve cell walls independent of the nitrogen level in the soil. Needle length was the only growth parameter that was very little reduced after one growing season of combined nitrogen-enriched soil and fumigation with high ozone concentrations. Foliar and stem nitrogen concentrations did not respond significantly to increased ozone levels.

A time-concentration study on the effects of ozone on spring wheat ( Triticum aestivumL.). : 3: Effects on leaf area and flag leaf senescence

Spring sown wheat ( Triticum aestivum L. cv. `Promessa') was exposed to different concentrations of ozone in open-top chambers over a three year period at a site in the south-east of Ireland. Filtered and non-filtered treatments were used in addition to fumigated treatments in which additional ozone was added to the non-filtered air. Ozone was added either as short term high concentration exposures or as long term low concentration exposures. In 1991, exposure to the A+50 (Ambient+50 ppb ozone) treatment resulted in a substantial reduction in the green leaf area index and enhanced both the onset and the rate of leaf yellowing. The A+50 treatment in 1993 also resulted in a reduction in green leaf area in addition to accelerating chlorophyll and soluble protein loss in flag leaves. This treatment caused a more gradual loss of chlorophyll and green leaf area in comparison to the same treatment in 1991 which received a greater amount of potentially damaging ozone. In contrast the A+25 treatment in 1992 delayed leaf yellowing and enhanced green leaf retention in comparison to the filtered control treatment. This treatment received the same total cumulative ozone exposure as the A+50 treatment in 1991 but was supplied as a lower concentration over a longer time interval. High concentrations applied over short time intervals proved more phytotoxic than identical exposures in which lower concentrations were applied over longer time intervals. Changes in leaf senescence and in leaf area index induced by ozone were closely paralleled by changes in the grain yield. The results suggest that changes in grain yield are the result of ozone induced alterations in leaf senescence which lead to changes in the leaf area available for photosynthate production.

Stress-physiological investigations and chromosomal analyses on cloned Norway spruce trees exposed to various levels of ozone in open-top chambers

Antioxidants and pigments in needles as well as chromosomal aberrations in root tip meristems of young clonal Picea abies trees were investigated after exposure to different ozone concentrations (charcoal filtered, non-filtered, non-filtered +25ppb, non-filtered +50ppb) in open-top chambers for three months. The same analyses were conducted after keeping the trees under ambient conditions for one year. Ozone treatments induced a dose dependent increases in chromosomal aberrations (up to nearly 10%) which could be found even after one year. Antioxidants and pigments in needles varied between sample times but differences among ozone treatments were not observed.

Differential response of buddleia ( Buddleia davidii Franch.) to ozone

Five cultivars of buddleia, Buddleia davidii Franch., were exposed to sub-ambient, ambient, and twice-ambient levels of ozone in open-top chambers for 8 weeks (June–August) during 1995: Plants were evaluated for foliar injury, growth index, and inflorescence characteristics during and following exposure. Destructive harvests were conducted at the end of the exposure period to determine dry weights of both above- and below-ground plant components. All cultivars had symptoms of visible injury in the twice-ambient treatment at both three and eight weeks after exposures began. No visible symptoms were observed at ambient ozone concentrations. At three weeks of exposure, ‘Pink Delight’ had the highest percentage of the leaves injured (PLI), 46.2%, followed by ‘Opera’ with a PLI of 23.3%. The other three cultivars had similar PLIs of less than 15%. After eight weeks of exposure, visible injury was equally severe on all cultivars with a mean PLI of 50.2% and mean Horsfall-Barratt rating of 5.4, indicating 12 to 25% of the leaf area was injured. No ozone × cultivar interaction was found for any growth variable measured. Across cultivars, growth index was reduced by 6%, total dry weight by 35%, and the number of developing floral buds and inflorescences by 29% for plants in twice-ambient ozone concentrations compared to ambient ozone concentrations. Percent biomass allocated to inflorescences was significantly greater for plants exposed to sub-ambient levels compared to those exposed to ozone at either ambient or twice-ambient concentrations. Results indicate that ozone levels similar to those in large urban areas in the southeastern United States have the potential to reduce growth and flowering of this important landscape plant.

OZONE SENSITIVITY OF BUDDLEIA CULTIVARS

Five cultivars of buddleia, Buddleia davidii, were exposed to subambient, ambient, and twice-ambient levels of ozone in open-top chambers for 8 weeks during 1995. Plants were evaluated for foliar injury, growth index, and inflorescence characteristics during and following the exposure period. Destructive harvests were conducted at the end of the exposure period to determine the dry weight of both above- and below-ground plant components. All cultivars showed signs of visible injury in the twice-ambient treatment at both 3 and 8 weeks after treatment initiation (WAT). At 3 WAT, `Pink Delight' was the most severely injured, followed by `Opera'. The other three cultivars had similar lower levels of foliar injury. Reductions in growth index as well as dry weight were found for all cultivars in the twice-ambient treatment. The number of developing floral buds and inflorescences was reduced in the twice-ambient treatment for all cultivars. Differences among the cultivars was due to normal differences in growth habit and not due to elevated ozone levels. These data indicate that Buddleia cultivars are sensitive to levels of ozone similar to those found in urban areas of the southeastern United States.

Exposure of a grass-clover mixture to ozone in open-top chambers—effects on yield, quality and botanical composition

A field-grown grass-clover mixture was exposed to four different levels of ozone in open-top chambers: filtered air, non-filtered air and non-filtered air with two different levels of ozone added. There was also an ambient air treatment with no chambers. The same pasture was exposed to ozone for two consecutive growing seasons. Three cuts per season were made. There was a negative relationship between yield and ozone concentration, and a significant regression was obtained between total dry weight yield for all six harvests and the Accumulated exposure Over Threshold 40 nl l −1 (AOT40) for the whole exposure period. Analysis of variance did not reveal significant ozone effects on quality parameters (fibre content, energy content, protein, Ca, Fe, Mo). Fibre content and botanical composition were, however, influenced by enclosure of the plants in the open-top chambers. The importance of the ozone concentration gradient above a field crop for the estimation of yield loss is discussed. It is hypothesised that the lower ozone sensitivity in pasture compared with wheat is due to the fact that pasture is harvested before natural senescence, while wheat is exposed during this ozone sensitive phase of plant development.

The Impact of Ozone on the15N Incorporation and Nitrogen Assimilation of Wheat and Maize

Abstract Young wheat (C3) and maize (C4) plants were exposed to near-ambient concentrations of ozone in open-top chambers in order to investigate the possible effects of ozone on nitrogen metabolism. Nitrogen was supplied to the plants by adding (15)N-labelled tracer substances via the soil substrate. Enzyme activities (NADH nitrate reductase, nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase) and the incorporation of (15)N were determined. The findings show that nitrogen metabolism was affected by O(3), however, there were distinct differences between the two species. In plants treated with O(3), NADH nitrate reductase activity in maize leaves was reduced, while NR activity in wheat leaves only slightly declined. Only minor changes were observed with respect to the activities of nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase. Feeding experiments using (15)NO(3) (-) showed that the incorporation of nitrate nitrogen in wheat plants exposed to ozone remains virtually unchanged, whereas in maize plants reduced incorporation rates were observed for nitrate nitrogen. The incorporation of ammonium nitrogen was distinctly increased in wheat and maize by the impact of ozone. When investigating pigment contents, reduced levels of chlorophyll a and b and carotenoids were observed, whereas the pigment content of wheat leaves remained unchanged. These results indicate that young maize plants are more susceptible than wheat plants to short-term ozone exposure.

Physiological responses of Fagus sylvatica L. exposed to low levels of ozone in open-top chambers

Four-year-old beech seedlings were fumigated with three levels of ozone for 2 consecutive years in open-top chambers. During the second growth season different physiological measurements were conducted before and during daily fumigation. A 25–40% decrease in net photosynthesis was seen during fumigation, whereas no differences were detected before fumigation in July. In August lasting effects in net photosynthesis were seen. The apparent quantum yield was decreased after fumigation. Stomatal conductance was generally decreased during fumigation, but transpiration was reduced relatively less than net photosynthesis indicating a lower water use efficiency of the trees exposed to ozone. Chlorophyll fluorescence (Fv/Fm) showed additive reductions in relation to ozone and light.

Mild ozone exposure alters (14)C dynamics in foliage of Pinus taeda L.

To explore the physiological mechanisms underlying ozone-induced growth reductions in loblolly pine (Pinus taeda L.), seedlings were exposed to sub-ambient (charcoal-filtered), ambient or twice-ambient ozone in open-top chambers for three growing seasons. In the final year of exposure, current-year needle fascicles were labeled with (14)CO(2) and the incorporation of (14)C into biochemical fractions was followed for 48 hours. Irrespective of ozone treatment, losses of (14)C-assimilates from foliage to respiration and translocation were minimal during the first 3 hours, whereas more than 60% of the label was lost during the next 45 hours. Radiolabel in sugar decreased rapidly after a lag period, roughly paralleling the pattern of total (14)C loss. The amount of (14)C label in starch and lipids plus pigments remained constant throughout the 48-hour chase period, whereas the amount of (14)C label in other fractions showed a net decrease over the 48-hour chase period. Ozone treatments altered foliar carbon dynamics in two ways: (1) ozone exposure increased foliar (14)C retention up to 21% for the first 5 hours after labeling, but not thereafter, and (2) ozone exposure decreased partitioning of (14)C into starch and increased partitioning of (14)C into organic acids, residue, and lipids plus pigments, indicating an intensified partitioning of carbon to injury and repair processes. Both short-term carbon retention and diversion of carbon from storage compounds to repair processes are foliar mechanisms by which ozone exposure could decrease growth in loblolly pine seedlings.

Yield and quality of spring barley, Hordeum vulgare L., exposed to different concentrations of ozone in open-top chambers

Spring barley ( Hordeum vulgare L., cv. ‘Lina’) was exposed to different concentrations of ozone in open-top chambers (OTCs) for 6 weeks following anthesis at a site located in south-west Sweden during the summer of 1989. The chambers were placed in a field of commercially grown barley. The treatments were charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air plus extra ozone (NF +). Presence of the OTCs reduced grain yield, number of ears per unit area, and 1000-grain weight, probably due to increased drought during the warm and dry weather in the summer of 1989. The chamber also increased the crude protein content of grain. These effects were, however, not statistically significant. Grain yield was not affected by 7 h day −1 seasonal mean ozone concentrations up to 45 nl l −1 (24 h seasonal mean = 22 nl l −1) compared to charcoal-filtered air. It is concluded that barley is likely to be less sensitive to ozone than wheat. The possible role of differences in the process of grain filling between the two species for the differences in ozone sensitivity is discussed.

Yield and grain quality of spring wheat ( Triticum aestivum L., cv. Drabant) exposed to different concentrations of ozone in open-top chambers

Spring wheat ( Triticum aestivum L., cv. Drabant) was exposed to different concentrations of ozone in open-top chambers for two growing seasons, 1987 and 1988, at a site located in south-west Sweden. The chambers were placed in a field of commercially grown spring wheat. The treatments were charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air plus extra ozone (NF +). In 1988, one additional ozone concentration (NF ++) was used. Grain yield was affected by the ozone concentration of the air. Air filtration resulted in an increase in grain yield of about 7% in both years, compared to NF. The addition of ozone (NF +, NF ++) reduced grain yield and increased the content of crude protein of the grain in both years. Filtration of the air had no significant effect on the content of crude protein, compared to NF. The results showed a strong positive chamber effect on grain yield in the cold and wet summer of 1987. In 1988, there was no net chamber effect on grain yield. The relative differences between the CF, NF and NF + treatments with respect to grain yield were of the same magnitude in the two years, despite the very different weather conditions.

Long-term exposure of Norway spruce, Picea abies (L.) Karst., to ozone in open top chambers: II. Effects on the ultrastructure of needles.

One clone of spruce, Picea abies (L.) Karst., was exposed to different concentrations of ozone in open-top chambers for three seasons. The treatments were filtered air (CF), non-filtered air (NF) and non-filtered air + ozone (NF+). Changes in ultrastructure occurring in the 1985 flush of needles were followed for three years. Ultrastructural changes due to ozone first occurred in the chloroplasts. A decrease in length of the chloroplasts, an increase of the density of the stroma, an accumulation of ribosome-like granules and a decrease in the size of starch grains, were observed. The second organelle to be affected was the microbody and the last the mitochondria. At this later stage the cytoplasm had also disintegrated. Structural changes always appeared first in the outer cell layer facing the sky. The changes then gradually advanced in the tissue towards the lower part of the needle. In the NF+ treatment changes were observed at the first sampling event in November, 1 month after the end of the first exposure period. At this time the needles were about 6 months old. In the NF treatment the same changes appeared when the needles were about 14 months old. No changes were observed in the CF treatment. Changes of the same type as those observed in the mesophyll tissue were also seen in stomatal and endodermal cells. In albuminous cells a general breakdown of the organelles was observed.

Yield response of red kidney bean Phaseolus vulgaris ti incremental ozone concentrations in the field

Field-grown red kidney beans were exposed to incremental levels of ozone in open-top chambers for 21 days during pod filling. Treatments consisted of ambient plots without chambers, chambers receiving charcoal-filtered air and chambers receiving non-filtered air to which either 0·00, 0·03, 0·06 or 0·09 ppm O 3 was added for 7 h each day. The addition of 0·06 or 0·09 ppm O 3 produced foliar injury, extensive defoliation and reductions in per plant bean yield of 24 and 27%, respectively. Regression analysis indicated a significant linear relationship between the 7-h mean O 3 concentration and yield per plant. This relationship was expressed as: Yield = 17·44 – 35·51 (CONC).