A quantitative assessment of hormetic responses of plants to ozone

Effect of elevated tropospheric ozone on methane and nitrous oxide emission from rice soil in north India

Sensitivity to tropospheric ozone is highly variable in cultivars of different plant species. Wheat, an important cereal crop, has been found to be sensitive to elevated ozone levels leading to differences in grain yields. The objective of this study was to compare the effects of elevated tropospheric ozone on growth, yield and nutritional quality of two species of wheat, Triticum aestivum (PBW 343) and Triticum durum (HD 2936), which are tropical wheat cultivars commonly grown in northern India. Experiments were conducted growing winter wheat (rabi season) under elevated tropospheric ozone in northern India for two years in open-top chambers (OTCs) under charcoal-filtered air (CF), non-filtered air (NF), open air (OA) and elevated ozone (EO) concentration (NF + 25-35 ppb O3). There were different species responses to EO, with the modern aestivum wheat cultivar being more sensitive than durum wheat. The declines in all growth and yield parameters were greater in T. aestivum than T. durum in both the years. On average there was a 7% greater reduction in the photosynthetic rate and stomatal conductance in T. aestivum as compared to T. durum under EO at the flowering stage, and a 6% more reduction in leaf chlorophyll was observed on T. aestivum as compared to T. durum. Exposure to elevated O3 caused a decrease in the number of leaves and leaf area index, rubisco enzyme activity and chlorophyll in both the species. More reductions in grain yield were observed in T. aestivum (15 and 19%) as compared to T. durum (9 and 13%) under EO in the two years, respectively. Filtration of air significantly increased all growth and yield parameters in both species of wheat.

It was shown that biphasic responses are commonly reported for opiates with respect to a broad range of animal models and endpoints. These endpoints include such diverse functions as blood pressure, muscle tension, breathing rates, hCG production, HIV production, neutrophil migration, ACTH production, protein binding, and neuronal functioning. Quantitative features of the dose-response relationships indicated that the maximum stimulatory responses were ≤3-fold greater than the controls with most being between 10 to 70% greater than the controls. In contrast to the striking similarity in the maximum stimulatory response, there was marked variation with respect to the dose range of the stimulatory responses that varied from 101 to 1010. Mechanistic assessments were conducted for most biphasic dose-response relationships and are addressed in detail.

Reactions of Norway spruce and beech trees to 2 years of ozone exposure and episodic drought

This chapter reviews the effects of elevated ozone on tree species in China, based on the results of studies in the past two decades. The high ozone concentration in summer in most parts of China has induced typical ozone symptoms in urban and mountain forest tree species. In experiments using open-top chambers, elevated ozone affected the growth, gas-exchange rate, foliar microscopy, antioxidant systems, and biogenic volatile organic compound (BVOC) emissions in trees. The effects of ozone on biomass accumulation depended on the ozone concentration, tree species sensitivity, and exposure duration. The ozone uptake of individual tree species was also investigated by the sap flow technique. Further studies were conducted on the interactions between O3 and other environmental change factors, such as increasing CO2 concentrations, increased nitrogen deposition, and drought. Future needs for research include the development of an O3 flux model for the most widely used tree species and the assessment of ozone removal by urban forests on a regional and a national scale.

Tropospheric ozone (O3) is widely recognized as the most critical, regional atmospheric pollutant causing significant losses to agricultural productivity due to its phytotoxicity over agricultural areas and is expected to increase in future. In view of rising tropospheric ozone concentration over Indian regions, the present study aimed to evaluate the effect of elevated ozone stress on pulse crop blackgram (Vigna mungo L.), which contributes the major share of protein. The blackgram varieties namely CO 6, VBN 1, VBN 2, VBN 3, VBN 5, VBN 6, VBN 7, and VBN 8 were grown in open top chambers and factorial completely randomized block design was followed. The plants were exposed to elevated ozone concentration (50 and 100 ppb) from 10.00 h to 17.00 h over 10 days at flowering stage, with a weighted average ozone concentration of 50.1 and 101.2 ppb. Both the elevated ozone treatments significantly affected the plant physiological, biochemical, growth, and yield traits of all test varieties. On an average across eight blackgram varieties, decrease in chlorophyll content by 33.83 and 42.41%, stomatal conductance by 28.25 and 40.51% and photosynthetic rate by 29.43 and 42.30% exposed to 50 and 100 ppb ozone were observed, respectively. Correspondingly, the number of pods per plant decreased by 30.82 and 32.65%, 100 grain weight by 7.75 and 21.23% and plant weight by 16.03 and 21.23%, respectively, which were significant at 5% level. Furthermore in the observed traits, significantly higher reduction was observed in VBN3, while the least reduction was observed in VBN8. The path analysis displayed that all the observed physiological, biochemical, growth, and yield traits positively regulated the yield except leaf injury percentage, malondialdehyde, and proline content. The principal component analysis of two elevated ozone treatments confirmed VBN8 as ozone tolerant and VBN3 as ozone sensitive variety. Hence, cultivation of VBN8 variety at ozone hotspot regions would be the best option to overcome ozone induced yield loss.

Fine-root morphology of woody and herbaceous plants responds differently to altered precipitation: A meta-analysis

Divergent arbuscular mycorrhizal growth responses in woody and herbaceous plants across inoculum richness

A lysimeter study was performed to monitor effects of elevated ozone on juvenile trees of Fagus sylvatica L. as well as on the plant–soil system. During a fumigation period over almost three growing seasons, parameters related to plant growth, phenological development and physiology as well as soil functions were studied. The data analyses identified elevated ozone to delay leaf phenology at early and to accelerate it at late developmental stages, to reduce growth, some leaf nutrients (Ca, K) as well as some soluble phenolics (hydroxycinnamic acid derivatives, total flavonol glycosides). No or very weak ozone effects were found in mobile carbon pools of leaves (starch, sucrose), and other phenolic compounds (flavans). Altered gene expression related to stress and carbon cycling corresponded well with findings from leaf phenology and chemical composition analyses indicating earlier senescence and oxidative stress in leaves under elevated ozone. Conversely in the soil system, no effects of ozone were detected on soil enzyme activities, rates of litter degradation and lysimeter water balances. Despite the fact that the three reported years 2003–2005 were climatically very contrasting including a hot and dry as well as an extremely wet summer, and also mild as well as cold winters, the influence of ozone on a number of plant parameters is remarkably consistent, further underlining the phytotoxic potential of elevated tropospheric ozone levels.

Effects of elevated carbon dioxide and ozone on potato tuber quality in the European multiple-site experiment ‘CHIP-project’

In this paper, to examine the effects of elevated ozone on secondary metabolism and antioxidant capacity in soybean roots, as well as reactive oxygen species and antioxidant enzymes activity. Soybean grown in open top chambers (OTCs) were exposed to ambient air ((O 3)=40nmolmol -1 ) and elevated ozone ((O3)=110±10nmolmol -1 ). The results revealed that with ozone concentration rising, compared with control, the O3 stress induced the total flavonoids content in soybean root of all treatments showed a significant rising trend (P<0.05), and the total polyphenols content showed a rising trend but not significant. The PAL and PPO activity of soybean root was always lower than that of CK, the LOX activity of soybean root was always higher than that of CK, but the PALˎLOX and PPO activity of soybean root expressed an increased trend with the increase of soybean growth period. However, variation of antioxidant enzymes activity in soybean roots was very different from each other. Superoxide dismutase (SOD) activity was lower than the CK treatment at flowering and podding stages under elevated ozone stress, it presents a volatility changes. During the whole growth stage, elevated ozone stress induced a decrease on activity of catalase (CAT) except for flowering stage, it had a significant increase (p<0.05), the ozone treatment was higher than the CK treatment in general except flowering stage. Activity of peroxidase (POD) was increased under elevated ozone. It had a higher representation (p<0.05) than the CK treatment at every stage. It can be concluded that the ozone stress has significant effects on soybean roots, and effects on soybean roots' normal growth.

Elevated ozone and CO2 can differentially affect the performance of plant species. Variation among native, exotic and invader species in their growth and defense responses to CO2 and ozone may shape CO2 and ozone effects on invasions, perhaps in part also due to variation between native and invasive populations of invaders. We manipulated ozone (control or 100 ppb) and CO2 (ambient or 800 ppm) in a factorial greenhouse experiment in replicated chambers. We investigated growth and defense (tannins) of seedlings of Triadica sebifera from invasive (USA) and native (China) populations and pairs of US and China tree species within three genera (Celtis, Liquidambar and Platanus). Overall, ozone reduced growth in ambient CO2 but elevated CO2 limited this effect. T. sebifera plants from invasive populations had higher growth than those from native populations in control conditions or the combination of elevated CO2 and ozone in which invasive populations had greater increases in growth. Their performances were similar in elevated CO2 because native populations were more responsive and their performances were similar with elevated ozone because invasive populations were more susceptible. Compared to other species, T. sebifera had high growth rates but low levels of tannin production that were insensitive to variation in CO2 or ozone. Both China and US Platanus plants reduced tannins with increased CO2 and/or ozone and US Liquidambar plants increased tannins with the combination of elevated CO2 and ozone. The growth results suggest that intraspecific variation in T. sebifera will reduce the effects of CO2 or ozone alone on invasions but increase their combined effects. The tannin results suggest that defense responses to CO2 and ozone will be variable across native and exotic species. The effects of CO2 and ozone on growth and defense of native and exotic species indicate that the benefit or harm to species from these global change drivers is an idiosyncratic combination of species origin and genus.

Landscape plants have great potentials in heavy metals (HMs) removal as sewage sludge compost (SSC) is increasingly used in urban forestry. We hypothesize that woody plants might perform better in HMs phytoremediation because they have greater biomass and deeper roots than herbaceous plants. We tested the differences in growth responses and HMs phytoremediation among several herbaceous and woody species growing under different SSC concentrations through pot experiments. The mixing percentage of SSC with soil at 0%, 15%, 30%, 60, and 100% were used as growth substrate for three woody (Ficus altissima Bl., Neolamarckia cadamba (Roxb.) Bosser, and Bischofia javanica Bl.) and two herbaceous (Alocasia macrorrhiza (L.) G. Don and Dianella ensifolia (L.) DC) plants. Results showed that the biomass, relative growth rate, and nutrient uptake for all plants increased significantly at each SSC concentration compared to the control; woody plants had higher biomass and nutrient use efficiency than herbaceous plants. All plants growing in SSC-amended soils accumulated appreciable amounts of HMs and reduced the contents of HMs present in the substrates. The woody plants were generally more effective than herbaceous plants in potentials of HMs phytoextraction, but A. macrorrhiza showed higher bioconcentration and translocation of Cu and Zn and D. ensifolia had higher bioconcentration and translocation of Cd than woody plants. The optimal application concentrations were 30% or less for woody plants and 15% for herbaceous plants for plant growth and ecological risk control, respectively. Intercropping suitable woody and herbaceous landscape plants in urban forestry might have promising potentials to minimize the ecological risks in the phytoremediation of SSC.

The co-occurrence of elevated tropospheric ozone concentrations and drought in agricultural regions is anticipated to increase with climate change. Both stressors negatively impact leaf photosynthetic capacity and stomatal conductance, contributing to reductions in biomass and yield. The interaction of ozone and drought stress is complex and under-researched, particularly in field settings. Stomatal closure in response to soil drying may provide protection from high ozone influx to leaves. Conversely, elevated ozone may prevent drought-induced stomatal closure, leading to depletion of soil water resources and exacerbation of drought stress. Here, we used Free Air Concentration Enrichment of ozone (100 ppb) and rainfall exclusion canopies (intercepting ∼40% of seasonal rainfall) to test potential interaction effects of elevated ozone and drought stress on soybean (Glycine max) leaf-level physiology and yield. Elevated ozone consistently reduced soybean Rubisco carboxylation capacity (-17%) and maximum electron transport capacity (-9%) across 3 yrs of study. Elevated ozone did not alter the relationships between soil moisture, abscisic acid, and stomatal conductance. Thus, there was no evidence indicating that ozone exposure prevented stomata from responding during drought. Yield was significantly reduced in soybeans exposed to elevated ozone, resulting from fewer seeds per plot and reduced seed size. The reduced precipitation treatment only affected yields in the driest growing season. These findings suggest that the effects of elevated ozone and drought are additive, rather than interactive, and dose dependent. The persistence of ozone damage under soil moisture depletion is likely to be exacerbated by global climate change.

Comparing different eco-physiological responses to atmospheric CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> enrichment between woody and herbaceous plants had profound meaning in speculating variation of vegetation composition and stand structure under global climate change. Based on the independent experiment results of 64 trees (39 genera) and 77 grasses (54 genera), the plant responses were summarized with a meta-analysis. In the study, it was found herbaceous plants would allot more increased biomass to above-ground parts which suggested elevated CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> maybe increase its coverage. Although photosynthesis rates of woody and herbaceous plants didn't significantly different, herbaceous total nonstructural carbohydrate as anabolic production was significantly more. It also showed that elevated CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> had significantly positive effects on water use efficiency in both herbaceous and woody plants, via reduction in stomotal conductance. Although the differences between their responses weren't significant, we could still detect in some aspects that herbaceous plants would be more benefited from increased atmospheric CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> than woody plants.