Phenylpropanoids are key players in the antioxidant defense to ozone of European ash, Fraxinus excelsior

Physiological and biochemical responses to ozone (O3) (150 ppb, 8 h day−1, 35 consecutive days) of two Italian provenances (Piedmont and Tuscany) of Fraxinus excelsior L. were evaluated, with special attention to the role of phenylpropanoids. Our results indicate (i) the high O3 sensitivity especially of Piedmont provenance (in terms of visible injury, water status, and photosynthetic apparatus); (ii) although the intra-specific sensitivity to O3 between provenances differs (mainly due to different stomatal behaviors since only Tuscany plants partially avoided the uptake of the pollutant gas), both provenances showed detoxification and defense mechanisms; (iii) the crucial participation of phenylpropanoids, with a key role played by flavonoids (especially quercitrin): among this class of metabolites, isoquercitrin is the principal player in the lower O3 sensitivity of Tuscany plants, together with lignins; (iv) although coumarins (typical compounds of Fraxinus) were severely depressed by O3, isofraxidin was triggered suggesting a key role in reactive oxygen species (ROS) detoxification, as well as trans-chalcone. Furthermore, the different behavior of verbascoside and oleuropein among provenances lead us to speculate on their influence in the tentatively repair or acclimation shown by Piedmont plants at the end of the exposure. Finally, the intra-specific O3 sensitivity may be also due to de novo peaks triggered by O3 not yet associated to some chemicals

Living in a Mediterranean city in 2050: broadleaf or evergreen ‘citizens’?

The predicted effects of global change (GC) will be exacerbated in the more densely populated cities of the future, especially in the Mediterranean basin where some environmental cues, such as drought and tropospheric ozone (O3) pollution, already mine seriously plant survival. Physiological and biochemical responses of a Mediterranean, evergreen, isohydric plant species (Quercus ilex) were compared to those of a sympatric, deciduous, anisohydric species (Q. pubescens) under severe drought (20% of the effective daily evapotranspiration) and/or chronic O3 exposure (80 ppb for 5 h dayâ1 for 28 consecutive days) to test which one was more successful in those highly limiting conditions. Results show that (i) the lower reduction of total leaf biomass of Q. ilex as compared to Q. pubescens when subjected to drought and drought à O3 (on average â59 vs â70%, respectively); (ii) the steeper decline of photosynthesis found in Q. pubescens under drought (â87 vs â81%) and drought à O3 (â69 vs â59%, respectively); (iii) the increments of malondialdehyde (MDA) by-products found only in drought-stressed Q. pubescens; (iv) the impact of O3, found only in Q. pubescens leaves and MDA, can be considered the best probes of the superiority of Q. ilex to counteract the effect of mild-severe drought and O3 stress. Also, an antagonistic effect was found when drought and O3 were applied simultaneously, as usually happens during typical Mediterranean summers. Our dataset suggests that on future, the urban greening should be wisely pondered on the ability of trees to cope the most impacting factors of GC, and in particular their simultaneity

Physiochemical responses of Ailanthus altissima under the challenge of Verticillium dahliae: elucidating the decline of one of the world’s worst invasive alien plant species

Natural infections of Verticillium spp. (Fungi, Ascomycota) on Ailanthus altissima have suggested to consider the biological control as a promising strategy to counteract this invasive plant, which is otherwise difficult to control by traditional mechanical and chemical treatments. Verticillium wilt is able to lead plants to death, throughout a pathogenic mechanism including vessel occlusions and production of degrading enzymes and phytotoxins. In this study, a 10 weeks open air pot experiment was set to investigate the ecophysiological and biochemical responses of Ailanthus trees artificially inoculated in the trunk with the V. dahliae strain VdGL16, previously isolated in Central Italy from the same host. Inoculated plants showed visible injuries starting from 2 weeks post inoculation (wpi), that progressively developed until a final severe defoliation. The fungal infection rapidly compromised the plant water status, and photosynthesis was impaired due to both stomatal and mesophyll limitations from 4 wpi, with subsequent detrimental effects also on PSII activity. Moreover, the disease altered the translocations of nutrients, as confirmed by cation and carbohydrate contents, probably due to a consumption of simple sugars and starch reserves without replacement of new photosynthesized. An accumulation of osmolytes (abscisic acid and proline) and phenylalanine (a precursor of phenylpropanoids) was also reported at 8 wpi, this being a response mechanism that needs to be further elucidated. However, the activation delay of such defence strategy inevitably did not avoid the premature defoliation of plants and the decline of physiochemical parameters, confirming the key role of Verticillium in Ailanthus decay

Cross‐Talk between Physiological and Metabolic Adjustments Adopted by Quercus cerris to Mitigate the Effects of Severe Drought and Realistic Future Ozone Concentrations

Global climate change represents a moving target for plant acclimation and/or adaptation, especially in the Mediterranean basin. In this study, the interactions of severe drought (20% of the effective daily evapotranspiration) and O3 fumigation (80 ppb, 5 h day−1, for 28 consecutive days) on (i) photosynthetic performance, (ii) cell membrane stability, (iii) hydric relations, (iv) accumulation of compatible solutes, and (v) lipophilic antioxidant compounds were investigated in young Quercus cerris plants. In addition to the typical drought-induced stomatal closure, imposition of water withholding dramatically influenced the profile of stress-associated metabolites, i.e., abscisic acid (ABA), proline, and lipophilic antioxidants. However, plants were not able to delay or prevent the negative effects of water deficit, the greatest impacting factor in this study. This translated into a steep decline of photosynthetic efficiency, leaf hydration, and membrane fluidity and permeability. When water stress was coupled with O3, plants orchestrated cross-talk among ABA, proline, and sugar in fully-expanded mature leaves, partially leading to a premature senescenc

Variations in physiological and biochemical traits of oak seedlings grown under drought and ozone stress

Despite the huge biodiversity characterizing the Mediterranean environment, environmental constraints, such as high sunlight and high temperatures alongside with dry periods, makes plant survival hard. In addition, high irradiance leads to increasing ozone (O3 ) concentrations in ambient air. In this era of global warming, it is necessary to understand the mechanisms that allow native species to tolerate these environmental constraints and how such mechanisms interact. Three Mediterranean oak species (Quercus ilex, Q. pubescens and Q. cerris) with different features (drought tolerant, evergreen or deciduous species) were selected to assess their biometrical, physiological and biochemical responses under drought and/or O3 stress (80-100 nl l(-1) of O3 for 5 h d(-1) for 77 consecutive days). Leaf visible injury appeared only under drought stress (alone or combined with O3 ) in all three species. Drought × O3 induced strong reductions in leaf dry weight in Q. pubescens and Q. cerris (-70 and -75%, respectively). Alterations in physiological (i.e. decrease in maximum carboxylation rate) and biochemical parameters (i.e. increase in proline content and build-up of malondialdehyde by-products) occurred in all the three species, although drought represented the major determinant. Q. ilex and Q. pubescens, which co-occur in dry environments, were more tolerant to drought and drought × O3 . Quercus ilex was the species in which oxidative stress occurred only when drought was applied with O3 . High plasticity at a biochemical level (i.e. proline content) and evergreen habitus are likely on the basis of the higher tolerance of Q. ilex

Losing the warning signal: Drought compromises the cross-talk of signaling molecules in quercus ilex exposed to ozone

Understanding the interactions between drought and acute ozone (O3) stress in terms of signaling molecules and cell death would improve the predictions of plant responses to climate change. The aim was to investigate whether drought stress influences the responses of plants to acute episodes of O3 exposure. In this study, the behavior of 84 Mediterranean evergreen Quercus ilex plants was evaluated in terms of crosstalk responses among signaling molecules. Half of the sample was subjected to drought (20% of the effective daily evapotranspiration, for 15 days) and was later exposed to an acute O3 exposure (200 nL L-1 for 5 h). First, our results indicate that in well-water conditions, O3 induced a signaling pathway specific to O3-sensitive behavior. Second, different trends and consequently different roles of phytohormones and signaling molecules (ethylene, ET; abscisic acid, ABA; salycilic acid, SA and jasmonic acid, JA) were observed in relation to water stress and O3. A spatial and functional correlation between these signaling molecules was observed in modulating O3-induced responses in well-watered plants. In contrast, in drought-stressed plants, these compounds were not involved either in O3-induced signaling mechanisms or in leaf senescence (a response observed in water-stressed plants before the O3-exposure). Third, these differences were ascribable to the fact that in drought conditions, most defense processes induced by O3 were compromised and/or altered. Our results highlight how Q. ilex plants suffering from water deprivation respond differently to an acute O3 episode compared to well-watered plants, and suggest new effect to be considered in plant responses to environmental changes. This poses the serious question as to whether or not multiple high-magnitude O3 events (as predicted) can change these cross-talk responses, thus opening it up possible further investigations

How Quercus ilex L. saplings face combined salt and ozone stress: a transcriptome analysis

Background: Similar to other urban trees, holm oaks (Quercus ilex L.) provide a physiological, ecological and social service in the urban environment, since they remove atmospheric pollution. However, the urban environment has several abiotic factors that negatively influence plant life, which are further exacerbated due to climate change, especially in the Mediterranean area. Among these abiotic factors, increased uptake of Na + and Cl − usually occurs in trees in the urban ecosystem; moreover, an excess of the tropospheric ozone concentration in Mediterranean cities further affects plant growth and survival. Here, we produced and annotated a de novo leaf transcriptome of Q. ilex as well as transcripts over- or under-expressed after a single episode of O3 (80 nl l-1, 5 h), a salt treatment (150mM for 15 days) or a combination of these treatments, mimicking a situation that plants commonly face, especially in urban environments. Results: Salinity dramatically changed the profile of expressed transcripts, while the short O3 pulse had less effect on the transcript profile. However, the short O3 pulse had a very strong effect in inducing over- or under-expression of some genes in plants coping with soil salinity. Many differentially regulated genes were related to stress sensing and signalling, cell wall remodelling, ROS sensing and scavenging, photosynthesis and to sugar and lipid metabolism. Most differentially expressed transcripts revealed here are in accordance with a previous report on Q. ilex at the physiological and biochemical levels, even though the expression profiles were overall more striking than those found at the biochemical and physiological levels. Conclusions: We produced for the first time a reference transcriptome for Q. ilex, and performed gene expression analysis for this species when subjected to salt, ozone and a combination of the two. The comparison of gene expression between the combined salt + ozone treatment and salt or ozone alone showed that even though many differentially expressed genes overlap all treatments, combined stress triggered a unique response in terms of gene expression modification. The obtained results represent a useful tool for studies aiming to investigate the effects of environmental stresses in urban-adapted tree species

Frequently asked questions about chlorophyll fluorescence, the sequel

[EN] Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122: 121-158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additionalChl a fluorescence-related topics are discussed again in a question and answer format. 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Studies of systematic uncertainties on the measurement of the muon anomalous magnetic moment at the Fermilab Muon g-2 experiment

The measurement of the muon magnetic anomaly aµ = (gµ−2/2), where g is the g-factor of the muon, is one of the most accurate tests of the Standard Model (SM) theory of elementary particles. This quantity is known at a very high precision (∼ 0.5 parts per million), both theoretically and experimentally. Dirac’s equation predicts gµ = 2 and therefore aµ = 0, whereas SM radiative corrections, dominated by the QED Schwinger term α/2π ≈ 0.00116, predict aµ with a total accuracy of 0.5 ppm, with the main source of uncertainty coming from the QCD sector. The E821 experiment at Brookhaven National Laboratory in 2001 measured aµ with an accuracy of 0.54 ppm and found a tantalizing difference of 3.7 standard deviations compared to the SM prediction. The purpose of the new Muon g-2 experiment E989 at Fermilab is to reduce the total experimental error by a factor of 4 to 0.14 ppm, by achieving a statistical and a systematic error of comparable size (0.1 ppm). When a muon is injected into a magnetic field, both its spin and its momentum vectors precede, and, since aµ != 0, the rate at which the spin turns relative to the momentum is ωa = aµ(e/m)B, namely “anomalous precession frequency”. This means that aµ can be extracted by accurately measuring ωa and B. In E989 experiment, positive muons are injected at the so-called “magic momentum” of 3.1 GeV/c into a storage ring of 14 m of diameter, in the presence of a vertical dipolar magnetic field of 1.45 T, with an average bunch rate of 12 Hz. The choice of the magic momentum (γµ ≈ 29.3) is such that the electric field of the vertically focusing quadrupoles does not affect ωa. Due to parity violation in the weak process of muon decay, high energy positrons are emitted preferably towards the muon’s spin direction and can be detected by 24 electromagnetic calorimeters placed along the inner radius of the ring. Each calorimeter can measure the energy and the arrival time of emitted positrons and is made up of 6×9 crystals of lead fluoride (PbF2) read by silicon photomultipliers (SiPM). If we count all emitted positrons with an energy above 1.7 GeV as a function of time, the counting rate oscillates with ωa frequency and its maximum occurs when the muon spin and momentum vectors are aligned. ωa can therefore be extracted by fitting the histogram of the oscillating number of counted positrons as a function of time, called also wiggle plot, with a 22-parameter function, which takes into account, amongst others, detector and beam dynamics effects. Muons are stored in the ring for 700 µs (“fill time”), which corresponds to almost 5000 turns of the muon beam in the ring, and to about 160 periods of the anomalous precession (T of anom. prec. = 4.4 µs). All effects that change over this time-scale affect the ωa measurement and must be well-known and accounted for in the fitting procedure. The work of this Thesis consisted in the discussion of the systematic effects affecting the ωa extraction for the first run of data in 2018 (Run1). Chapter 1 introduces the subject of the anomalous magnetic moment of the muon. Chapter 2 describes the current status of the SM theoretical prediction, and reviews some possible New Physics scenarios. Chapter 3 reviews the history of the muon g −2 experiments and Chapter 4 gives an overview on the E989 experiment, focusing on the improvements that were necessary to reach the design goal on the measurement of aµ. Chapter 5 discusses the different sources of systematic error on ωa measurement, starting from the ones that originate from detector effects: Pileup, that occurs when two positrons hit the same calorimeter crystal very close in time, and Gain instability of the SiPMs during fill time. There are also systematic effects due to beam dynamics, that are parametrized in the fitting function: the Coherent Betatron Oscillation (CBO), both in the radial and vertical directions, and Lost Muons, which are muons that exit the storage ring due to their imperfect trajectory, lowering the number of emitted positrons during fill time. The so-called E-field and Pitch corrections affect ωa as well, because not all muons travel at the magic momentum and their trajectory is not always perpendicular to the magnetic field. Chapter 6, which is the original part of the Thesis, introduces the so-called “Phase Acceptance” (PA) effect, which, due to the limited calorimeter acceptance in the presence of magnetic field, affects the reconstructed phase of the muon spin when positrons are emitted from different beam positions around the ring. This effect, which is larger for Run1 due to damaged quadrupole resistors that affected RC time constants on beam dynamics parameters, fixed in Run2, turned out to be one of the largest and unexpected contribution to the ωa uncertainty. The analysis of the PA effect uses data from Run1 and from Monte Carlo simulation: many studies were performed to establish the size of the contribution on ωa and its uncertainty. For the whole Run1 dataset, the PA affects ωa at the level of O(100 ppb) with an uncertainty of ∼ 40 ppb, whereas, for Run2, preliminary studies showed that the impact of PA was less than 50 ppb

Responses of oak species to single and combined abiotic stresses in the global climate change era

In this era of global warming it is necessary to understand the mechanisms that allow native plant species to tolerate these environmental constraints and the way such mechanisms interact. The main scope of this research work was to investigate the responses of oak species to single and combined abiotic stresses that are common in the Mediterranean urban environments (drought, O3 and salinity). Firstly, three Mediterranean oak species (Querucs ilex, Q. pubescens and Q. cerris) with different features (drought tolerance, evergreen or deciduous species) were selected in order to assess their responses under a long period of moderate drought (30% of the effective daily evapotranspiration) and/or O3 stress (80 ppb of O3 for 5 h d-1 for 77 consecutive days). The chronic O3 treatment had a minor impact compared to drought, highlighting that the plasticity of the species is dependent on the environment in which they live. Species that inhabit environments characterized by long periods of water deficiency (i.e. Q. ilex and Q. pubescens) are usually more plastic under the same stress compared with those that rarely face the same environmental constraint (Q. cerris). Furthermore, this dataset shows that biochemical and physiological adjustments may reduce the impact of O3 when combined with the effect of drought. Following the results came out from this first experiment, and since the mitigative effect of drought against O3 seems more consistent when plant is exposed to short and harsh period of severe drought rather than to longer O3 exposure but under moderate drought, other two sets of experiments were performed. Firstly, the interactions of severe drought (20% of the effective daily evapotranspiration) and O3 (80 ppb, 5 h d-1, for 28 consecutive days) were investigated in Q. cerris focusing on its hydric relations, synthesis/production of compatible solutes and lipophilic antioxidant compounds. Although, leaf-intrinsic adjustments occurred (stomatal limitations) and the synthesis of stress-associated metabolites was altered, plants were not able to delay or prevent the negative impact of drought. Furthermore, it was evident that drought alone induced fairly higher effects in comparison to O3, whereas when O3 was applied together with drought it showed some “mitigating effects” against limited water availability. In fact, plants of Q. cerris exposed to both drought and O3 seemed able to partially adjust and optimize their photosynthetic activity. This response could be interpreted as a photosynthetic acclimation leading to a premature senescence of fully-developed leaves as a strategy to respond to multiple stress conditions, likely addressed to alert younger leaves. Later, physiological and biochemical responses of Q. ilex (evergreen, isohydric species) were compared to those of the sympatric Q. pubescens (deciduous, anisohydric species) under the same environmental constrains of the previous experiment. This study confirms the higher ability of evergreen species to counteract the effect of drought and O3 when compared to deciduous species in Mediterranean environment. This ability of evergreens seems to be correlated with the stronger necessity of these species, which inhabits usually unfavorable environments, to protect their long-lived leaves from several negative environmental factors. This peculiarity seems less relevant for highly-demanding, fast-growing deciduous species characterized by shorter leaf lifespan, which have superior fitness than evergreens in non-limiting environment. Then, the response of Q. ilex (the most studied oak species, as well as the species that has been shown the higher tolerance and plasticity in the first experiment) to drought (20% of the effective daily evapotranspiration) and/or an acute O3-exposure (200 ppb, 5 h) was also investigated. This study, which focused on the interaction between reactive oxygen species (ROS), phytohormones and signalling molecules to evaluate if the response of Q. ilex resembles the biotic defense reactions, shows that: (i) in well-watered conditions, O3 induced a signalling pathway similar to that triggered by a pathogen only in terms of ROS pattern (showing an O3-sensitive behavior); (ii) different trends and consequently different roles of phytohormones and signalling molecules were observed in relation to the leaf hydric status and O3 (applied both singularly and consequently), and (iii) these differences were ascribable to the fact that in drought conditions most defense processes induced by O3 were compromised/altered. Furthermore, the response of Q. ilex was also investigated also under salinity and O3. Q. ilex saplings were firstly exposed to salinity (150 mM NaCl, 15 days), and the effect on photosynthesis, hydric relations and ion partitioning were evaluated (Experiment I). Then, salt-treated plants were exposed to 80 ppb of O3 for 5 h (Experiment II). The results of the first experiment indicate that evergreen sclerophylls such as Q. ilex, with their long-lived leaves have a low photosynthetic efficiency on a mass basis because these species invest preferentially in vascular and cell wall formation. This induces these species to decrease intercellular spaces and increase cell wall thickness, increasing CO2 drawdown but also maintaining high foliar RWC and osmotic stress tolerance. These mechanisms are consistent with a conservative strategy adopted by Q. ilex to preserve its long-lived leaves against different abiotic stresses. Furthermore, the dataset of the second experiment shows that O3 did not exacerbate the oxidative stress observed in salt-treated plants although a further relevant enhancement of the Halliwell-Asada cycle was necessary to counteract the O3-induced damage when the leaf status was already negatively affected by a previous salt exposure. This harmonic response is an extra burden for plants, and growth can suffer as a result in the long-term, if these single O3 episodes take place repeatedly. Assessing the impact of climate change and air pollution on ecosystems is still a challenging task and the development of adequate monitoring techniques is necessary for assessing vegetation status. Thus, a final study was performed showing that reflectance spectroscopy can be an alternative method for monitoring leaf water potential and also making a posteriori measurements of pre-dawn leaf water potential (PDΨW) on tropical live oak Q. oleoides sampled in four Central American populations (Belize, Costa Rica, Honduras and Mexico) and grown under differential water availability. This study confirms that spectroscopic approaches are quick and non-destructive, providing the possibility to screen more samples in the field and over multiple time periods. In addition, this dataset demonstrates that spectroscopic retrievals of PDΨW in response to environmental variation (e.g. water availability) can be used as a surrogate for standard approaches