Abstract
There is growing evidence to demonstrate that air pollution is affecting invertebrates both directly (e.g., causing physiological stress responses) and indirectly (e.g., via changes in host plant chemistry and/or by disruption of communication by volatile odours). Many of the studies to-date have focused upon winged insects and disruption of in-flight foraging. Therefore, in this study we investigated how the community composition of predominantly ground-dwelling invertebrates in fields of winter wheat are affected by two of the most ubiquitous lower tropospheric air pollutants, diesel exhaust emissions (including nitrogen oxides–NOx) and ozone (O3), both individually and in combination, over 2 years. Pitfall traps, located within the rings of a Free-Air Diesel and Ozone Enrichment (FADOE) facility, were used to sample invertebrates. The facility consisted of eight 8 m-diameter rings, which allowed elevation of the pollutants above ambient levels (ca 49–60 ppb NOx and 35–39 ppb O3) but within levels currently defined as safe for the environment by the Environmental Protection Agency. The invertebrates collected were taxonomically identified and characterised by diet specialisation, mobility and functional group. Taxonomic richness and Shannon’s diversity index were calculated. Even under the relatively low levels of air pollution produced, there were adverse impacts on invertebrate community composition, with greater declines in the abundance and taxonomic richness of invertebrates in the diesel exhaust treatment compared with O3 treatment. In the combined treatment, pollutant levels were lower, most likely because NOx and O3 react with one another, and consequently a lesser negative effect was observed on invertebrate abundance and taxonomic richness. Specialist-feeding and winged invertebrate species appeared to be more sensitive to the impacts of the pollutants, responding more negatively to air pollution treatments than generalist feeders and wingless species, respectively. Therefore, these results suggest a more severe pollution-mediated decline in specialist- compared with generalist-feeding invertebrates, and in more mobile (winged) individuals. Understanding how invertebrate communities respond to air pollutants alone and in combination will facilitate predictions of how terrestrial environments respond to changes in anthropogenic emissions, especially as we shift away from fossil fuel dependence and therefore manipulate the interactions between these two common pollutants.
Highlights
Insects and other invertebrates provide a myriad of essential ecosystem services that create the biological foundation for all terrestrial ecosystems (Scudder, 2017)
O3 mixing ratios in the D + O3 treatment were similar to those in the Control treatment during both time periods (Supplementary Figures 1C,D) and mixing ratios of NOx and the ratio of nitric oxide (NO)/NO2 significantly decreased under D + O3, compared with the D treatment, during the complete and the experimental periods (Supplementary Figures 1A,B, respectively)
Our results demonstrated that both diesel exhaust and O3 pollution had adverse impacts on invertebrate community composition, in the combined pollution treatment O3 exposure mitigated the negative effects of diesel exhaust emission on invertebrate abundance and taxonomic richness
Summary
Insects and other invertebrates provide a myriad of essential ecosystem services (e.g., nutrient cycling, maintenance of soil structure and fertility, pest control, pollination and seed dispersal) that create the biological foundation for all terrestrial ecosystems (Scudder, 2017). Recent research has proposed a role for common air pollutants, e.g., diesel exhaust [ nitrogen oxides—NOx, comprised of nitric oxide (NO) and nitrogen dioxide (NO2)] and ozone (O3), as a further threat to ecosystem function. These pollutants can impair the fitness of invertebrates, both directly via pollution-induced molecular and physiological changes (Leonard et al, 2019; Reitmayer et al, 2019; Thimmegowda et al, 2020; Vanderplanck et al, 2021), and indirectly via changes to the nutritional status of host plants or by chemically altering the odour compounds that invertebrates use for navigation (e.g., to locate plants or invertebrate hosts) and communication (Fuentes et al, 2016; Jamieson et al, 2017; Jürgens and Bischoff, 2017). A basic understanding of how air pollution alters invertebrate community composition and functional group (e.g., feeding guild) dynamics would enable us to predict effects of future pollution scenarios on plant– invertebrate systems, which could be used to influence policy to mitigate impacts on ecosystem function (Couture and Lindroth, 2013; Li et al, 2016)
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