Effects Of Elevated Ozone Research Articles

Effects of elevated ozone on photosynthesis and stomatal conductance of two soybean varieties: a case study to assess impacts of one component of predicted global climate change

Global climatic change scenarios predict a significant increase in future tropospheric ozone (O(3)) concentrations. The present investigation was done to assess the effects of elevated O(3) (70 and 100 ppb) on electron transport, carbon fixation, stomatal conductance and pigment concentrations in two tropical soybean (Glycine max L.) varieties, PK 472 and Bragg. Plants were exposed to O(3) for 4 h.day(-1) from 10:00 to 14:00 from germination to maturity. Photosynthesis of both varieties were adversely affected, but the reduction was higher in PK 472 than Bragg. A comparison of chlorophyll a fluorescence kinetics with carbon fixation suggested greater sensitivity of dark reactions than light reactions of photosynthesis to O(3) stress. The O(3)-induced uncoupling between photosynthesis and stomatal conductance in PK 472 suggests the reduction in photosynthesis may be attributed to a factor other than reduced stomatal conductance. An increase in internal CO(2) concentration in both O(3)-treated soybean varieties compared suggests that the reduction in photosynthesis was due to damage to the photosynthetic apparatus, leading to accumulation of internal CO(2) and stomatal closure. The adverse impact of O(3) stress increased at higher O(3) concentrations in both soybean varieties leading to large reductions in photosynthesis. This study suggests that O(3)-induced reductions in photosynthesis in tropical and temperate varieties are similar.

Performance and Secondary Chemistry of Two Hybrid Aspen (Populus tremula L. x Populus tremuloides Michx.) Clones in Long-Term Elevated Ozone Exposure

The effects of moderately elevated ozone (ca. 35 ppb) on the growth and secondary chemistry of the leaves of two soil-grown Finnish hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) clones with different ozone sensitivities were studied at an open-air exposure field in Kuopio, Finland. Stomatal conductance, photosynthetic rate, and chlorophyll fluorescence were measured during the third growing season. Foliar phenolic concentrations, ergosterol concentration of fine roots, and final dry mass of the trees were determined at the end of the third growing season. Elevated ozone increased the ectomycorrhizal status of the fine roots but had no effect on gas exchange or on the final biomass of either of the clones, indicating equal sensitivity to ozone and no effect of elevated ozone on the intraspecific competitive ability of the clones after three growing seasons. However, in agreement with the data from potted plants of the same clones after two growing seasons, significant differences between the clones were found in all parameters measured. A negative correlation between growth and high concentrations of foliar phenolics indicated that allocation to secondary chemistry also was costly in terms of growth under high resource availability.

Effects of elevated ozone on growth and yield of field-grown rice in Yangtze River Delta, China

With rapid industrialization and urbanization in the Yangtze Delta, China, the tropospheric ozone concentration has increased to levels that induce crop yield loss. Rice, a widely grown crop in China, was investigated in field-established, open-top chambers. Four treatments were used: charcoal-filtered air (CF), non-charcoal-filtered air (NF), and charcoal-filtered air with two levels of additional ozone (O3-1 and O3-2). The AOT40s (accumulated hourly mean ozone concentration above 40 ppbv) were 0, 0.91, 23.24, and 39.28 ppmv x h for treatment of CF, NF, O3-1, and O3-2, respectively. The rice height and biomass were reduced in the elevated ozone concentration. Less organic matter partitioning to roots under the elevated ozone significantly decreased rice root activity. The yield loss was 14.3% and 20.2% under O3-1 and O3-2 exposure, respectively. This was largely caused by a reduction in grain weight per panicle.

Interactive effects of elevated ozone and springtime frost on growth and physiology of birch (Betula pendula) in field conditions

We studied the impact of ozone enrichment and late frost, singly and interactively, on four birch (Betula pendula Roth) families selected from a naturally regenerated birch stand in southeastern Finland. Seedlings were exposed to 1.5× ambient ozone over one and a half growing seasons using free-air ozone enrichment system. Simulated springtime frost was implemented at the beginning of the second study year, 4 weeks after the bud burst. Plants were measured for timing of bud burst, visible ozone injuries, chlorophyll fluorescence, net photosynthesis and concentrations of photosynthetic pigments, as well as for growth and carbon allocation. Frost treatment caused a rapid 60% decline in net photosynthesis. The recovery of net photosynthesis from acute frost treatment was not complete during the subsequent 3 weeks, which led to significant growth reductions, decreased shoot/root ratio and accumulation of excess nitrogen in the leaves. Photosynthetic responses to ozone were very variable and family-specific. Concentrations of photosynthetic pigments were sensitive to both stress factors, while the maximum quantum yield of PSII was unaffected. Ozone exacerbated the effect of frost only on diameter increment. However, ozone and frost affected different seedling characters, e.g., ozone reduced pigments and frost collapsed net photosynthesis, and these effect combined appear to damage birch seedlings more than a single stress situation.

Effects of elevated ozone on chlorophyll a fluorescence in symptomatic and asymptomatic leaves of two tomato genotypes

Two different genotypes of Lycopersicon esculentum Mill. (cv. Cuor di Bue, O3-sensitive and line 93.1033/1, O3-resistant) were treated with a single dose of ozone (150 mm3 m−3 for 3 h). The PS 2 activity was examined by measurements of chlorophyll a fluorescence on symptomatic and asymptomatic leaves. Symptoms were evident on the 4th leaves from the bottom, in both genotypes, while the 2nd leaves of the line 93.1033/1 were asymptomatic. In these leaves, the net photosynthetic rate (PN) did not change even if the Fv/Fm ratio significantly decreased. A strong reduction in PN, mostly due to the stomatal closure, was observed in Cuor di Bue. The non photochemical quenching coefficient (qNP) and the degree of PS 2 reaction centres closure (1-qP) were higher, while the quantum efficiency of PS 2 photochemistry (ΦPS2) and quantum efficiency of excitation energy capture (Φexc.) were lower in O3 treated leaves of both genotypes. The limitation of photosynthesis was shown also by a decrease in the parameter %P, which diminished compared to controls in both genotypes. The response of the two genotypes for the energy fraction dissipated as thermal energy in the PS 2 antennae (%D) was similar. The fraction of %P remained lower during the recovery in symptomatic leaves of the resistant line as compared to the controls, whereas %X, which represents the amount of light energy that is not utilized in photochemistry or dissipated in the PS 2 antennae, significantly rose in the asymptomatic leaves of this line and in both the leaves of Cuor di Bue. From data obtained we concluded that ozone affected the plants independently on the appearance of visible symptoms of injury because the leaves without visible symptoms of both the genotypes were negatively influenced.

Pesticides and Health Effects: Karpati et al. Respond

In her letter, Ziem raises the issue of exacerbations of respiratory illness and other health effects of pesticide exposure that we did not measure in our study (Karpati et al. 2004). Our analysis was designed to evaluate only whether a population-level effect on emergency department visits, specifically on asthma and other respiratory illnesses, was evident following pyrethroid pesticide spraying. Similar study designs, despite their limitations, have proven to be sensitive methods of identifying population-level health impacts from exposure to criteria air pollutants from exposure to unusual events, such as smoke from forest fires. Moreover, our analysis did identify adverse population-level health effects of elevated ozone and particulates. As we noted in our discussion, the results of the analysis for pesticide exposure do not rule out the possibility that certain individuals might have been affected by exposure to the agent. Also, our focus was on emergency department visits, which generally signify more serious illness, although in urban neighborhoods even milder illnesses are often treated in such settings. However, if, in fact, certain individuals experienced asthma exacerbations following exposure, we believe our study demonstrates that their number was small enough that it did not result in a population-level increase in emergency department visits for asthma and chronic obstructive pulmonary disease. In our analysis we evaluated only respiratory complications of pesticide spraying to control West Nile virus, and we did not purport to measure possible neurotoxic or other nonrespiratory effects. Also, we did not evaluate the efficacy of pesticide spraying for mosquito control or its cost–benefit ratio with regard to pesticide-related health effects.

Effects of elevated ozone on leaf δ13C and leaf conductance of plant species grown in semi-natural grassland with or without irrigation

Stable carbon isotope ratios ( δ 13C) and leaf conductance ( g s) were measured (2002, 2003) in Holcus lanatus L., Plantago lanceolata L. Ranunculus friesianus (Jord.), and Trifolium pratense L. at two levels of ozone (O 3) with or without irrigation. In non-irrigated control plots, R. friesianus showed the least negative δ 13C, and the smallest response to the treatments. Irrigation caused more negative δ 13C, especially in H. lanatus. Irrespective of irrigation, O 3 increased δ 13C in relationship to a decrease in g s in P. lanceolata and T. pratense. The strongest effect of O 3 on δ 13C occurred in the absence of irrigation, suggesting that under field conditions lack of moisture in the top soil does not always lead to protection from O 3 uptake. It is concluded that in species such as T. pratense plants can maintain stomatal O 3 uptake during dry periods when roots can reach deeper soil layers where water is not limiting.

Effects of elevated ozone and low light on diurnal and seasonal carbon gain in sugar maple

AbstractThe long‐term interactive effects of ozone and light on whole‐tree carbon balance of sugar maple (Acer saccharum Marsh.) seedlings were examined, with an emphasis on carbon acquisition, foliar partitioning into starch and soluble sugars, and allocation to growth. Sugar maple seedlings were fumigated with ambient, 1·7 × ambient and 3·0 × ambient ozone in open‐top chambers for 3 years under low and high light (15 and 35% full sunlight, respectively). Three years of ozone fumigation reduced the total biomass of seedlings in the low‐ and high‐light treatments by 64 and 41%, respectively, but had no effect on whole‐plant biomass allocation. Ozone had no effect on net photosynthesis until late in the growing season, with low‐light seedlings generally exhibiting more pronounced reductions in photosynthesis. The late‐season reduction in photosynthesis was not due to impaired stomatal function, but was associated more with accelerated senescence or senescence‐like injury. In contrast, the 3·0 × ambient ozone treatment immediately reduced diurnal starch accumulation in leaves by over 50% and increased partitioning of total non‐structural carbohydrates into soluble sugars, suggesting that injury repair processes may be maintaining photosynthesis in late spring and early summer at the expense of storage carbon. The results in the present study indicate that changes in leaf‐level photosynthesis may not accurately predict the growth response of sugar maple to ozone in different light environments. The larger reduction in seedling growth under low‐light conditions suggests that seedlings in gap or closed‐canopy environments are more susceptible to ozone than those in a clearing. Similarly, understanding the effects of tropospheric ozone on net carbon gain of a mature tree will require scaling of leaf‐level responses to heterogeneous light environments, where some leaves may be more susceptible than others.

Ozone sensitivity, growth and flower development in Phleum genotypes of different geographic origin in the Nordic countries

Nine genotypes of Phleum pratense, with origins ranging from the southernmost part of Denmark to the Scandian mountains and the coast of the Barents sea, and three genotypes of Phleum alpinum, all from the boreal region of north Sweden, were exposed to four treatments: charcoal and purafil filtered air with or without an addition of 140 g m −3 ozone, and non-filtered air with or without an addition of 100 g m −3 ozone, in open-top chambers. Plants were also grown in the ambient air to be able to control the influence of the chamber climate. Filtration of the air did not significantly affect plant growth or flowering. In terms of growth reduction, P. alpinum was more sensitive to the elevated ozone concentration than P. pratense, but the effects of elevated ozone on P. pratense were also large and significant. The ozone sensitivity of P. pratense genotypes did not vary systematically with the geographical origin but covaried with the growth rate. The higher temperature in the open-top chambers had a positive effect on biomass production of genotypes from the sites with the highest summer temperatures, while it affected negatively growth and flowering in most of the genotypes from the sites with the lowest summer temperature. On average, the higher temperatures in the open-top chambers affected positively the average aboveground biomass production of the P. pratense genotypes, while the development of flowers was slightly negatively affected.

Effects of elevated ozone on CO2 uptake and leaf structure in sugar maple under two light environments

The interactive effects of ozone and light on leaf structure, carbon dioxide uptake and short‐term carbon allocation of sugar maple (Acer saccharum Marsh.) seedlings were examined using gas exchange measurements and 14C‐macroautoradiographic techniques. Two‐year‐old sugar maple seedlings were fumigated from budbreak for 5 months with ambient or 3 × ambient ozone in open‐top chambers, receiving either 35% (high light) or 15% (low light) of full sunlight. Ozone accelerated leaf senescence, and reduced net photosynthesis, 14CO2 uptake and stomatal conductance, with the effects being most pronounced under low light. The proportion of intercellular space increased in leaves of seedlings grown under elevated ozone and low light, possibly enhancing the susceptibility of mesophyll cells to ozone by increasing the cumulative dose per mesophyll cell. Indeed, damage to spongy mesophyll cells in the elevated ozone × low light treatment was especially frequent. 14C macroautoradioraphy revealed heterogeneous uptake of 14CO2 in well defined areole regions, suggesting patchy stomatal behaviour in all treatments. However, in seedlings grown under elevated ozone and low light, the highest 14CO2 uptake occurred along larger veins, while interveinal regions exhibited little or no uptake. Although visible symptoms of ozone injury were not apparent in these seedlings, the cellular damage, reduced photosynthetic rates and reduced whole‐leaf chlorophyll levels corroborate the visual scaling of whole‐plant senescence, suggesting that the ozone × low light treatment accelerated senescence or senescence‐like injury in sugar maple.

Whole-plant 14C-photosynthate allocation in Pinustaeda: seasonal patterns at ambient and elevated ozone levels

The seasonal patterns of carbon gain and allocation were examined in Pinustaeda L. seedlings grown under field conditions. To investigate how ozone stress may influence whole-plant carbon budgets over the growing season, the seedlings were grown in either ambient air or air enriched with ozone at twice-ambient levels. On five sampling dates during the 1987 growing season, seedlings were labeled with 14CO2, and whole-plant carbon budgets were constructed. Rate of assimilation of CO2 varied by a factor of 2 during the growing season, with a late spring maximum during the first growth flush. Respiratory losses were highest in the spring and then declined sharply during the summer when photosynthate allocation to the foliage increased rapidly. A second major shift in the carbon budget occurred in the autumn when allocation to the fine roots increased at the expense of the foliage. The proportion of photosynthate allocated to coarse roots and stems varied only slightly over the growing season. Allocation to any plant component was highest when growth of that component was at a maximum. No statistically significant effects of elevated ozone on either carbon gain or photosynthate allocation were detected at any specific time during the growing season. However, seedlings grown at twice-ambient ozone levels consistently exhibited the following trends: (i) lower rates of CO2 assimilation, (ii) greater allocation of photosynthate to respiration, and (iii) corresponding reduction in photosynthate allocation to fine roots. An individual-fascicle 14C-labeling technique was found to reflect the seasonal patterns of carbon import and export by foliage and thus may serve as an acceptable surrogate for whole-tree tagging. The pronounced seasonality of the carbon budgets in P. taeda in conjunction with a pattern of ozone effects on carbon assimilation and photosynthate allocation suggests that whole-plant carbon budgets are sensitive and biologically meaningful indicators of seedlings' responses to anthropogenic changes in atmospheric chemistry.