The magpie and the grapes: increasing ozone exposure impacts fruit consumption by a common corvid in a suburban environment.

BACKGROUND: The Eurasian magpie Pica pica is a resident bird species able to colonize farmlands and anthropized environments. This corvid shows a wide trophic spectrum by including fruits, invertebrates, small vertebrates and carcasses in its diet. A camera-trap experiment was carried out to test the effect of different ozone (O3 ) concentrations on potted Vitis vinifera plants, which resulted in different grape consumption rates by suburban birds. The test was performed at an Ozone-Free Air Controlled Exposure (FACE) facility, consisting of nine plots with three ozone (O3 ) levels: AA (ambient O3 concentration); and two elevated O3 levels, 1.5× AA (ambient air with a 50% increase in O3 concentration) and 2.0× AA (ambient air with a 100% increase in O3 concentration). Camera-traps were located in front of each treatment area and kept active for 24 h day-1 and for 5 days at a time over a period of 3 months to monitor grape consumption by birds. RESULTS: We collected a total of 38 videos. Eurasian magpies were the only grape consumers, with a total of 6.7 ± 3.3 passages per hour (mean ± SD) and no differences across the different O3 treatments. Grapes in the AA treatment were consumed significantly more quickly than those in the 1.5× AA treatment, which in turn, were consumed faster than those in the 2.0× AA treatment. At 3 days from the start of treatment, 94%, 53% and 22% berries from the AA, 1.5× AA and 2.0× AA treatments had been eaten, respectively. When the O3 was turned off, berries were consumed at the same rate among treatments. CONCLUSION: Increasing O3 concentrations limited grape consumption by magpies probably because O3 acted as a deterrent for magpies, although the lower sugar content recorded in the 2.0× AA berries did not affect the consumption when O3 was turned off. Our results provided valuable insights to mitigate human-wildlife conflicts in suburban environments. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The functional significance of the stomatal size to density relationship: Interaction with atmospheric [CO2] and role in plant physiological behaviour.

The limits for stomatal conductance are set by stomatal size (SS) and density (SD). An inverse relationship between SS and SD has been observed in fossil and living plants. This has led to hypotheses proposing that the ratio of SS to SD influences the diffusion pathway for CO2 and degree of physiological stomatal control. However, conclusive evidence supportive of a functional role of the SS-SD relationship is not evident, and patterns in SS-SD may simply reflect geometric constraints in stomatal spacing over a leaf surface. We examine published and new data to investigate the potential functional significance of the relationship between SS and SD to atmospheric [CO2] in multiple generation adaptive responses and short-term acclamatory adjustment of stomatal morphology. Consistent patterns in SS and SD were not evident in fossil and living plants adapted to high [CO2] over many generations. However, evolutionary adaptation to [CO2] strongly affected SS and SD responses to elevated [CO2], with plants adapted to the 'low' [CO2] of the past 10 million years (Myr) showing adjustment of SS-SD, while members of the same species adapted to 'high' [CO2] showed no response. This may suggest that SS and SD responses to future [CO2] will likely constrain the stimulatory effect of 'CO2-fertilisation' on photosynthesis. Angiosperms generally possessed higher densities of smaller stomata that corresponded to a greater degree of physiological stomatal control consistent with selective pressures induced by declining [CO2] over the past 90 Myr. Atmospheric [CO2] has likely shaped stomatal size and density relationships alongside the interaction with stomatal physiological behaviour. The rate and predicted extent of future increases in [CO2] will have profound impacts on the selective pressures shaping SS and SD. Understanding the trade-offs involved in SS-SD and the interaction with [CO2], will be central to the development of more productive climate resilient crops.

Publisher Correction: Impaired photosynthesis and increased leaf construction costs may induce floral stress during episodes of global warming over macroevolutionary timescales.

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Impaired photosynthesis and increased leaf construction costs may induce floral stress during episodes of global warming over macroevolutionary timescales.

Global warming events have coincided with turnover of plant species at intervals in Earth history. As mean global temperatures rise, the number, frequency and duration of heat-waves will increase. Ginkgo biloba was grown under controlled climatic conditions at two different day/night temperature regimes (25/20 °C and 35/30 °C) to investigate the impact of heat stress. Photosynthetic CO2-uptake and electron transport were reduced at the higher temperature, while rates of respiration were greater; suggesting that the carbon balance of the leaves was adversely affected. Stomatal conductance and the potential for evaporative cooling of the leaves was reduced at the higher temperature. Furthermore, the capacity of the leaves to dissipate excess energy was also reduced at 35/30 °C, indicating that photo-protective mechanisms were no longer functioning effectively. Leaf economics were adversely affected by heat stress, exhibiting an increase in leaf mass per area and leaf construction costs. This may be consistent with the selective pressures experienced by fossil Ginkgoales during intervals of global warming such as the Triassic - Jurassic boundary or Early Eocene Climatic Optimum. The physiological and morphological responses of the G. biloba leaves were closely interrelated; these relationships may be used to infer the leaf economics and photosynthetic/stress physiology of fossil plants.

Land use and wind direction drive hybridization between cultivated poplar and native species in a Mediterranean floodplain environment.

Deforestation and intensive land use management with plantations of fast-growing tree species, like Populus spp., may endanger native trees not only by eliminating or reducing their habitats, but also by diminishing their species integrity via hybridization and introgression. The genus Populus has persistent natural hybrids because clonal and sexual reproduction is common. The objective of this study was to assess the effect of land use management of poplar plantations on the spatial genetic structure and species composition in poplar stands. Specifically, we studied the potential breeding between natural and cultivated poplar populations in the Mediterranean environment to gain insight into spontaneous hybridization events between exotic and native poplars; we also used a GIS-based model to evaluate the potential threats related to an intensive land use management. Two study areas, both near to poplar plantations (P.×euramericana), were designated in the native mixed stands of P. alba, P. nigra and P.×canescens within protected areas. We found that the spatial genetic structure differed between the two stands and their differences depended on their environmental features. We detected a hybridization event with P.×canescens that was made possible by the synchrony of flowering between the poplar plantation and P.×canescens and facilitated by the wind intensity and direction favoring the spread of pollen. Taken together, our results indicate that natural and artificial barriers are crucial to mitigate the threats, and so they should be explicitly considered in land use planning. For example, our results suggest the importance of conserving rows of trees and shrubs along rivers and in agricultural landscapes. In sum, it is necessary to understand, evaluate, and monitor the spread of exotic species and genetic material to ensure effective land use management and mitigation of their impact on native tree populations.

Testing a ratio of photosynthesis to O3 uptake as an index for assessing O3-induced foliar visible injury in poplar trees.

Visible foliar injury by ozone (ozone visible injury) is known as a biomarker to assess potential phytotoxicity of ozone. We investigated ozone visible injury in an ozone-sensitive poplar (Oxford clone) under a 2-year free-air controlled exposure (FACE) experiment and calculated three ozone indices (i.e., accumulative ozone exposure over 40 ppb during daylight hours (AOT40), phytotoxic ozone dose above a flux threshold of 0 nmol m-2 s-1 (POD0), and the cumulative value of the ratio of hourly ozone uptake to net photosynthesis (ΣU/P n ) to assess the critical level (CL) at the time of the first symptom onset of ozone visible injury. We tested the hypothesis that ozone injury depends both on the amount of ozone entering a leaf and on the capacity for biochemical detoxification or repair with photosynthesis as a proxy. The CLs at the time of the first symptom onset of ozone visible injury were 19 ppm h for AOT40, 26 mmol m-2 for POD0, and 1.2 mol mol-1 for ΣU/P n in Oxford clone at the ozone FACE experiment. Our findings were then verified by 4-year observation-based data in central Italy on Oxford clone and white poplar (Populus alba L.). These observation-based data indicated that we found ozone visible injury in Oxford clone even though AOT40 was relatively low (11.7 ppm h). On the other hand, when values of POD0 and ΣU/P n exceeded over the CLs, the occurrence of initial symptoms in Oxford clone was shown. White poplar did not show ozone visible injury. ΣU/P n of white poplar at the field sites reached ~1.0 mol mol-1 (less than the CL = 1.2 mol mol-1, which was obtained from O3 FACE) during May-September, although the values of POD0 were relatively high in white poplar (44-47 mmol m-2 during May-September). The result implies that ozone injury may have occurred in poplars when stomatal ozone flux exceeded the critical range of tolerance due to the assimilate shortage for repair and defense against ozone stress.

A new-generation 3D ozone FACE (Free Air Controlled Exposure).

To artificially simulate the impacts of ground-level ozone (O3) on vegetation, ozone FACE (Free Air Controlled Exposure) systems are increasingly recommended. We describe here a new-generation, three-dimensional ozone FACE, with O3 diffusion through laser-generated micro-holes, pre-mixing of air and O3, O3 generator with integral oxygen generator, continuous (day/night) exposure and full replication. Based on three O3 levels and assumptions on the pre-industrial O3 levels, we describe principles to calculate relative yield/biomass and estimate impacts even at lower-than-ambient O3 levels. The case study is called FO3X, and is at present the only ozone FACE in Mediterranean climate and one of the very few ozone FACEs investigating more than one stressor at a time. The results presented here will give further impulse to the research on O3 impacts on vegetation all over the world.

Impaired Stomatal Control Is Associated with Reduced Photosynthetic Physiology in Crop Species Grown at Elevated [CO2].

Physiological control of stomatal conductance (Gs) permits plants to balance CO2-uptake for photosynthesis (PN) against water-loss, so optimizing water use efficiency (WUE). An increase in the atmospheric concentration of carbon dioxide ([CO2]) will result in a stimulation of PN and reduction of Gs in many plants, enhancing carbon gain while reducing water-loss. It has also been hypothesized that the increase in WUE associated with lower Gs at elevated [CO2] would reduce the negative impacts of drought on many crops. Despite the large number of CO2-enrichment studies to date, there is relatively little information regarding the effect of elevated [CO2] on stomatal control. Five crop species with active physiological stomatal behavior were grown at ambient (400 ppm) and elevated (2000 ppm) [CO2]. We investigated the relationship between stomatal function, stomatal size, and photosynthetic capacity in the five species, and then assessed the mechanistic effect of elevated [CO2] on photosynthetic physiology, stomatal sensitivity to [CO2] and the effectiveness of stomatal closure to darkness. We observed positive relationships between the speed of stomatal response and the maximum rates of PN and Gs sustained by the plants; indicative of close co-ordination of stomatal behavior and PN. In contrast to previous studies we did not observe a negative relationship between speed of stomatal response and stomatal size. The sensitivity of stomata to [CO2] declined with the ribulose-1,5-bisphosphate limited rate of PN at elevated [CO2]. The effectiveness of stomatal closure was also impaired at high [CO2]. Growth at elevated [CO2] did not affect the performance of photosystem II indicating that high [CO2] had not induced damage to the photosynthetic physiology, and suggesting that photosynthetic control of Gs is either directly impaired at high [CO2], sensing/signaling of environmental change is disrupted or elevated [CO2] causes some physical effect that constrains stomatal opening/closing. This study indicates that while elevated [CO2] may improve the WUE of crops under normal growth conditions, impaired stomatal control may increase the vulnerability of plants to water deficit and high temperatures.

Coordination of stomatal physiological behavior and morphology with carbon dioxide determines stomatal control.

PREMISE OF THE STUDY: Stomatal control is determined by the ability to alter stomatal aperture and/or the number of stomata on the surface of new leaves in response to growth conditions. The development of stomatal control mechanisms to the concentration of CO2within the atmosphere ([CO2]) is fundamental to our understanding of plant evolutionary history and the prediction of gas exchange responses to future [CO2]. METHODS: In a controlled environment, fern and angiosperm species were grown in atmospheres of ambient (400 ppm) and elevated (2000 ppm) [CO2]. Physiological stomatal behavior was compared with the stomatal morphological response to [CO2]. KEY RESULTS: An increase in [CO2] or darkness induced physiological stomatal responses ranging from reductions (active) to no change (passive) in stomatal conductance. Those species with passive stomatal behavior exhibited pronounced reductions of stomatal density in new foliage when grown in elevated [CO2], whereas species with active stomata showed little morphological response to [CO2]. Analysis of the physiological and morphological stomatal responses of a wider range of species suggests that patterns of stomatal control to [CO2] do not follow a phylogenetic pattern associated with plant evolution. CONCLUSIONS: Selective pressures may have driven the development of divergent stomatal control strategies to increased [CO2]. Those species that are able to actively regulate guard cell turgor are more likely to respond to [CO2] through a change in stomatal aperture than stomatal number. We propose a model of stomatal control strategies in response to [CO2] characterized by a trade-off between short-term physiological behavior and longer-term morphological response.