New Insights into Leaf Physiological Responses to Ozone for Use in Crop Modelling

Estimating food production under future air pollution and climate conditions in scenario analysis depends on accurately modelling ozone (O₃) effects on yield. This study tests several assumptions that form part of published approaches for modelling O₃ effects on photosynthesis and leaf duration against experimental data. In 2015 and 2016, two wheat cultivars were exposed in eight hemispherical glasshouses to O₃ ranging from 22 to 57 ppb (24 h mean), with profiles ranging from raised background to high peak treatments. The stomatal O₃ flux (Phytotoxic Ozone Dose, POD) to leaves was simulated using a multiplicative stomatal conductance model. Leaf senescence occurred earlier as average POD increased according to a linear relationship, and the two cultivars showed very different senescence responses. Negative effects of O₃ on photosynthesis were only observed alongside O₃-induced leaf senescence, suggesting that O₃ does not impair photosynthesis in un-senesced flag leaves at the realistic O₃ concentrations applied here. Accelerated senescence is therefore likely to be the dominant O₃ effect influencing yield in most agricultural environments. POD was better than 24 h mean concentration and AOT40 (accumulated O₃ exceeding 40 ppb, daylight hours) at predicting physiological response to O₃, and flux also accounted for the difference in exposure resulting from peak and high background treatments

Evaluation of simulated biomass damage in forest ecosystems induced by ozone against observation-based estimates

Regional estimates of the effects of ozone pollution on forest growth depend on the availability of reliable damage functions that estimate a representative ecosystem response to ozone exposure. A number of such damage functions for forest tree species and forest functional types have recently been published and subsequently applied in terrestrial biosphere models to estimate regional or global effects of ozone on forest tree productivity and carbon storage in the living plant biomass. The resulting impacts estimated by these biosphere models show large uncertainty in the magnitude of ozone effects predicted. To understand the role that these damage functions play in determining the variability of estimated ozone impacts, we use the O-CN biosphere model to provide a standardised modelling framework. We test four published damage functions describing the leaf-level, photosynthetic response to ozone exposure (targeting Vcmax or net photosynthesis) in terms of their simulated whole-tree biomass responses against field data from 23 ozone filtration/fumigation experiments conducted with European tree species at sites across Europe with a range of climatic conditions. Our results show that none of these previously published damage functions lead to simulated whole-tree biomass reductions in agreement with the observed dose-response relationships derived from these field experiments, and instead lead to significant over- / or underestimations of the ozone effect. By reparameterising these photosynthetic based damage functions we develop linear, plant functional type specific dose-response relationships, which provide accurate simulations of the observed whole-tree biomass response across these 23 experiments

Ozone pollution will compromise efforts to increase global wheat production

Introduction of high-performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain-fed and irrigated areas of major wheat-producing countries (e.g. United States, France, India, China and Russia). Averaged over 2010–2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above-mentioned UN SDG, while also contributing to other SDGs related to human health and well-being, ecosystems and climate change

A single-point modeling approach for the intercomparison and evaluation of ozone dry deposition across chemical transport models (Activity 2 of AQMEII4)

A primary sink of air pollutants and their precursors is dry deposition. Dry deposition estimates differ across chemical transport models, yet an understanding of the model spread is incomplete. Here, we introduce Activity 2 of the Air Quality Model Evaluation International Initiative Phase 4 (AQMEII4). We examine 18 dry deposition schemes from regional and global chemical transport models as well as standalone models used for impact assessments or process understanding. We configure the schemes as single-point models at eight Northern Hemisphere locations with observed ozone fluxes. Single-point models are driven by a common set of site-specific meteorological and environmental conditions. Five of eight sites have at least 3 years and up to 12 years of ozone fluxes. The interquartile range across models in multiyear mean ozone deposition velocities ranges from a factor of 1.2 to 1.9 annually across sites and tends to be highest during winter compared with summer. No model is within 50 % of observed multiyear averages across all sites and seasons, but some models perform well for some sites and seasons. For the first time, we demonstrate how contributions from depositional pathways vary across models. Models can disagree with respect to relative contributions from the pathways, even when they predict similar deposition velocities, or agree with respect to the relative contributions but predict different deposition velocities. Both stomatal and nonstomatal uptake contribute to the large model spread across sites. Our findings are the beginning of results from AQMEII4 Activity 2, which brings scientists who model air quality and dry deposition together with scientists who measure ozone fluxes to evaluate and improve dry deposition schemes in the chemical transport models used for research, planning, and regulatory purposes

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Impacts of tropospheric ozone and climate change on Mexico wheat production

Wheat is an important staple crop sensitive to negative effects from elevated tropospheric ozone (O3) concentrations, but the impacts of future O3 concentrations on wheat production in Mexico are unknown. To determine these impacts, the O3-modified DSSAT-NWheat crop model was used to simulate wheat production in Mexico using a baseline scenariowith pre-industrial O3 concentrations from 1980 to 2010 and five Global Climate Models (GCMs) under the Representative Concentration Pathway (RCP) 8.5 scenario from 2041 to 2070 paired with future O3 concentrations from the European Monitoring and Evaluation Programme (EMEP) Meteorological Synthesizing Centre–West (MSC-W) model. Thirty-two representative major wheat-producing locations in Mexico were simulated assuming both irrigated and rainfed conditions for two O3 sensitivity cultivar classifications. The simulations showed large variability (after averaging over 30 years) in yield loss, ranging from 7 to 26% because of O3 impact, depending on the location, irrigation, and climate change emissions scenario. After upscaling and aggregating the simulations to the country scale based on observed irrigated and rainfed production, national wheat production for Mexico is expected to decline by 12% under the future RCP 8.5 climate change scenario with additional losses of 7 to 18% because of O3 impact, depending on the cultivar O3 sensitivity. This yield loss caused by O3 is comparable with, or even larger than, the impact from projected future climatic change in temperature, rainfall, and atmospheric CO2 concentration. Therefore, O3 impacts should be considered in future agricultural impact assessments

Ozone effects on crops and consideration in crop models

We review current knowledge of the processes by which ozone will cause injury and damage in crop plants. We do this both through an understanding of the limitations to ozone uptake (i.e. ozone being transferred from some height in the atmosphere to the leaf boundary layer and subsequent uptake via the stomata) as well as through the internal plant processes that will result in damage and /or injury. We consider these processes across the range of scales that are impacted in the plant, from cellular injury and damage (that can result in visible injury and alterations to photosynthesis and stomatal conductance) through to leaf level impacts on physiology and leaf senescence and ultimately to alterations in whole plant canopy and root systems that will affect biogeochemical cycling within the plant. We consider these processes from the viewpoint of developing crop growth models that are capable of incorporating key ozone impact processes within modelling structures that asses crop growth under a variety of different stresses. This would provide a dynamic assessment of the impact of ozone on crop growth within the context of other key variables considered important in determining crop growth and yield. We consider the ability to achieve this through an assessment of the different types of crop model (e.g. empirical, radiation use efficiency, and photosynthesis based crop growth models. Finally, we show how international activities such as the AgMIP (Agricultural Modelling and Improvement Intercomparison Project) could provide a network of crop growth modellers to assess the capabilities of different crop models to simulate the effects of ozone and other stresses to improve future regional and global risk assessments

Idiosyncratic trends of woodland invertebrate biodiversity in Britain over 45 years

•1. Woodland cover in Britain has increased over the past century and is set to increase further through woodland creation schemes aiming to tackle climate change. Nonetheless, the wider repercussions of increasing woodland cover for species, especially invertebrates, have not been comprehensively assessed. •2. Here, we quantified the woodland associations of 2762 invertebrate species in Britain across 21 broad taxon groups using species occurrence records collected by specialist recording societies. We then related the strength of species' woodland associations to published estimates of their long-term national distribution trends between 1970 and 2015. •3. Across all taxa, 29% of species were positively associated with broadleaf woodland cover, whereas 27% of species were negatively associated. There was a slight tendency for species associated with broadleaf woodland to have more positive long-term distribution trends, but the effect had little explanatory power. For 15% of species, we detected a non-monotonic association with broadleaf woodland cover, such that their occurrence peaked at intermediate levels of cover. Intermediate-cover species had more positive long-term distribution trends than species with monotonic positive or negative woodland associations. •4. Our findings suggest that woodland invertebrates have not consistently increased, despite the increases in woodland cover. While some caution is warranted owing to our use of heterogeneous occurrence records, the considerable variation in distribution trends of woodland-associated species could be explained by the high diversity of woodland species and ways in which they use woodland habitat. Woodland creation, or increasing tree cover in general, could have idiosyncratic impacts on species, depending on how new woodlands are created and managed