Plant defences mediate interactions between herbivory and the direct foliar uptake of atmospheric reactive nitrogen

Simulated nitrogen deposition enhances resistance of female poplars over males to Pestalotiopsis microspora infection through the recruitment of antagonistic microbes in phyllosphere

Atmospheric nitrogen deposition has globally increased due to human activities and has strongly interfered with plant growth and resistance to biotic stressors. Dioecious plant species have shown secondary dimorphism in growth and development between male and female individuals in response to increased nitrogen deposition. However, the extent to whether these sexual differences influence variations in phyllosphere microbial communities and the associated pathogen resistance between male and female conspecifics remains unclear. To address this knowledge gap, female and male full-sibs of a poplar species were exposed to simulated nitrogen deposition and then artificially infected with a leaf pathogenic fungus, Pestalotiopsis microspora. The findings revealed that simulated nitrogen deposition promoted the growth of both sexes, with male plants exhibiting superior growth. Following P. microspora infection, female control plants displayed a greater leaf lesion area compared to males, but simulated nitrogen deposition reversed this difference. Further phyllosphere microbiome analysis and toxicity test indicated that the sexual differences in pathogen resistance between male and female conspecifics were likely attributable to alterations in the composition and structure of epiphytic microbes as the phyllosphere of female plants harbored a higher abundance of ecologically beneficial microbes with potential biological control capabilities, whereas males exhibited an increase abundance in the phytopathogens genera in response to simulated nitrogen deposition. Confirmatively, two bacterial strains were successfully isolated from the epiphytic phyllosphere of female plants that exhibited strong antagonistic effect against the pathogenic fungus P. microspora in both in vitro and in vivo conditions. The findings have significant implications for the selection of suitable poplar sexes for landscaping and reforestation efforts in areas experienced severe atmospheric nitrogen deposition.

Tripartite interactions of an endophytic entomopathogenic fungus, Asian corn borer, and host maize under elevated carbon dioxide

BACKGROUND

Biological control of insect pests is encountering an unprecedented challenge in agricultural systems due to the ongoing rise in carbon dioxide (CO2) level. The use of entomopathogenic fungi (EPF) in these systems is gaining increased attention, and EPF as crop endophytes hold the potential for combining insect pest control and yield enhancement of crops, but the effects of increased CO2 concentration on this interaction are poorly understood. Here, the introduction of endophytic EPF was explored as an alternative sustainable management strategy benefiting crops under elevated CO2, using maize (Zea mays), Asian corn borer (Ostrinia furnacalis), and EPF (Beauveria bassiana) to test changes in damage to maize plants from O. furnacalis, and the nutritional status (content of carbon, nitrogen, phosphorus, potassium), biomass, and yield of maize.

RESULTS

The results showed that endophytic B. bassiana could alleviate the damage caused by O. furnacalis larvae for maize plants under ambient CO2 concentration, and this effect was enhanced under higher CO2 concentration. Inoculation with B. bassiana effectively counteracted the adverse impact of elevated CO2 on maize plants by preserving the nitrogen content at its baseline level (comparable with ambient CO2 conditions without B. bassiana). Both simultaneous effects could explain the improvement of biomass and yield of maize under B. bassiana inoculation and elevated CO2.

CONCLUSION

This finding provides key information about the multifaceted benefits of B. bassiana as a maize endophyte. Our results highlight the promising potential of incorporating EPF as endophytes into integrated pest management strategies, particularly under elevated CO2 concentrations. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Nitrogen-mediated volatilisation of defensive metabolites in tomato confers resistance to herbivores

Plants synthesise a vast array of volatile organic compounds (VOCs), which serve as chemical defence and communication agents in their interactions with insect herbivores. Although nitrogen (N) is a critical resource in the production of plant metabolites, its regulatory effects on defensive VOCs remain largely unknown. Here, we investigated the effect of N content in tomato (Solanum lycopersicum) on the tobacco cutworm (Spodoptera litura), a notorious agricultural pest, using biochemical and molecular experiments in combination with insect behavioural and performance analyses. We observed that on tomato leaves with different N contents, S. litura showed distinct feeding preference and growth and developmental performance. Particularly, metabolomics profiling revealed that limited N availability conferred resistance upon tomato plants to S. litura is likely associated with the biosynthesis and emission of the volatile metabolite α-humulene as a repellent. Moreover, exogenous application of α-humulene on tomato leaves elicited a significant repellent response against herbivores. Thus, our findings unravel the key factors involved in N-mediated plant defence against insect herbivores and pave the way for innovation of N management to improve the plant defence responses to facilitate pest control strategies within agroecosystems.

Towards a mechanistic understanding of the impacts of nitrogen deposition on producer-consumer interactions

Nitrogen (N) deposition has increased substantially since the second half of the 20th century due to human activities. This increase of reactive N into the biosphere has major implications for ecosystem functioning, including primary production, soil and water chemistry and producer community structure and diversity. Increased N deposition is also linked to the decline of insects observed over recent decades. However, we currently lack a mechanistic understanding of the effects of high N deposition on individual fitness, species richness and community structure of both invertebrate and vertebrate consumers. Here, we review the effects of N deposition on producer-consumer interactions, focusing on five existing ecological frameworks: C:N:P ecological stoichiometry, trace element ecological stoichiometry, nutritional geometry, essential micronutrients and allelochemicals. We link reported N deposition-mediated changes in producer quality to life-history strategies and traits of consumers, to gain a mechanistic understanding of the direction of response in consumers. We conclude that high N deposition influences producer quality via eutrophication and acidification pathways. This makes oligotrophic poorly buffered ecosystems most vulnerable to significant changes in producer quality. Changes in producer quality between the reviewed frameworks are often interlinked, complicating predictions of the effects of high N deposition on producer quality. The degree and direction of fitness responses of consumers to changes in producer quality varies among species but can be explained by differences in life-history traits and strategies, particularly those affecting species nutrient intake regulation, mobility, relative growth rate, host-plant specialisation, ontogeny and physiology. To increase our understanding of the effects of N deposition on these complex mechanisms, the inclusion of life-history traits of consumer species in future study designs is pivotal. Based on the reviewed literature, we formulate five hypotheses on the mechanisms underlying the effects of high N deposition on consumers, by linking effects of nutritional ecological frameworks to life-history strategies. Importantly, we expect that N-deposition-mediated changes in producer quality will result in a net decrease in consumer community as well as functional diversity. Moreover, we anticipate an increased risk of outbreak events of a small subset of generalist species, with concomitant declines in a multitude of specialist species. Overall, linking ecological frameworks with consumer life-history strategies provides a mechanistic understanding of the impacts of high N deposition on producer-consumer interactions, which can inform management towards more effective mitigation strategies.

Exogenous Salicylic Acid Alleviates NO2 Damage by Maintaining Cell Stability and Physiological Metabolism in Bougainvillea × buttiana 'Miss Manila' Seedlings

Exogenous substances can alleviate plant damage under adverse conditions. In order to explore whether different concentrations of salicylic acid (SA) can play a role in the resistance of Bougainvillea × buttiana 'Miss Manila' to nitrogen dioxide (NO2) stress and the relevant mechanisms of their effects, different concentrations of SA were applied locally under the control experiment condition of 4.0 μL·L-1 NO2, and the role of SA in alleviating injury was studied. The findings noted a significant increase in metabolic adaptations and antioxidant enzyme activities following 0.25-0.75 mM SA application (p < 0.05), except 1 mM. Superoxide dismutase (SOD) and catalase (CAT) in particular increased by 21.88% and 59.71%, respectively. Such an increase led to effective control of the reduction in photosynthetic pigments and the photosynthetic rate and protection of the structural stability of chloroplasts and other organelles. In addition, the activity of nitrate reductase (NR) increased by 83.85%, and the content of nitrate nitrogen (NO3--N) decreased by 29.23% in nitrogen metabolism. Concurrently, a principal component analysis (PCA) and a membership function analysis further indicated that 0.75 mM SA provided the most notable improvement in NO2 resistance among the different gradients. These findings suggest that 0.25-0.75 mM SA can relieve the stress at 4 μL·L-1 NO2 injury by effectively improving the antioxidant enzyme activity and nitrogen metabolizing enzyme activity, protecting the photosynthetic system and cell structure, but 1 mM SA had the opposite effect. In the future, the specific reasons for inhibition of SA at high concentrations and the comprehensive effects of the application of other exogenous compounds should be further studied.

Phytoremediation as a potential technique for vehicle hazardous pollutants around highways

With the synchronous development of highway construction and the urban economy, automobiles have entered thousands of households as essential means of transportation. This paper reviews the latest research progress in using phytoremediation technology to remediate the environmental pollution caused by automobile exhaust in recent years, including the prospects for stereoscopic forestry. Currently, most automobiles on the global market are internal combustion vehicles using fossil energy sources as the primary fuel, such as gasoline, diesel, and liquid or compressed natural gas. The composition of vehicle exhaust is relatively complex. When it enters the atmosphere, it is prone to a series of chemical reactions to generate various secondary pollutants, which are very harmful to human beings, plants, animals, and the eco-environment. Despite improving the automobile fuel quality and installing exhaust gas purification devices, helping to reduce air pollution, the treatment costs of these approaches are expensive and cannot achieve zero emissions of automobile exhaust pollutants. The purification of vehicle exhaust by plants is a crucial way to remediate the environmental pollution caused by automobile exhaust and improve the environment along the highway by utilizing the ecosystem's self-regulating ability. Therefore, it has become a global trend to use phytoremediation technology to restore the automobile exhaust pollution. Now, there is no scientific report or systematic review about how plants absorb vehicle pollutants. The screening and configuration of suitable plant species is the most crucial aspect of successful phytoremediation. The mechanisms of plant adsorption, metabolism, and detoxification are reviewed in this paper to address the problem of automobile exhaust pollution.

Breeding in the pandemic: short-term lockdown restrictions in a European capital city did not alter the life-history traits of two urban adapters

Humans are transforming natural habitats into managed urban green areas and impervious surfaces at an unprecedented pace. Yet the effects of human presence per se on animal life-history traits are rarely tested. This is particularly true in cities, where human presence is often indissociable from urbanisation itself. The onset of the SARS-CoV-2 outbreak, along with the resulting lockdown restrictions, offered a unique, "natural experiment" to investigate wildlife responses to a sudden reduction in human activity. We analysed four years of avian breeding data collected in a European capital city to test whether lockdown measures altered nestbox occupancy and life-history traits in terms of egg laying date, incubation duration and clutch size in two urban adapters: great tits (Parus major) and blue tits (Cyanistes caeruleus). Lockdown measures, which modulated human presence, did not influence any of the life-history traits investigated. In contrast, the interaction between year and tree cover, a distinct ecological attribute of the urban space, was positively associated with clutch size, a key avian life-history and reproductive trait. This highlights the importance of inter-year variation and habitat quality over human activity on urban wildlife reproduction. We discuss our results in the light of other urban wildlife studies carried out during the pandemic, inviting the scientific community to carefully interpret all lockdown-associated shifts in biological traits.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11252-022-01309-5.

Population dynamics of herbivorous insects in polluted landscapes

Environmental pollution is one cause of insect decline in the Anthropocene, but the underlying mechanisms remain obscure due to a paucity of pollution-impact studies on insects that address density-dependent processes. Long data series (19-26 years) are available only for a few species monitored around two industrial polluters in north-western Russia. A particularly exciting current finding is that industrial pollution determines the relative strength of rapid (stabilising) and delayed (destabilising) density dependence operating on a herbivore population. Most studies address acute effects of traditional pollutants (e.g. sulphur dioxide and trace elements) and nitrogen deposition on agricultural pests, whereas the effects of realistic concentrations of ozone, particulate matter and emerging pollutants on insects feeding on noncultivated plants are unknown. The accumulated evidence remains insufficient to predict the effects of pollutants of global concern on the population dynamics of herbivorous insects.

Ozone Mitigates the Adverse Effects of Diesel Exhaust Pollutants on Ground-Active Invertebrates in Wheat

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.

Decline of Eulia ministrana (Lepidoptera: Tortricidae) in polluted habitats is not accompanied by phenotypic stress responses

Environmental pollution is currently identified as one of the major drivers of rapid decline of insect populations, and this finding has revitalized interest in insect responses to pollution. We tested the hypothesis that the pollution-induced decline of insect populations can be predicted from phenotypic stress responses expressed as morphological differences between populations inhabiting polluted and unpolluted sites. We explored populations of the brassy tortrix Eulia ministrana in subarctic forests along an environmental disturbance gradient created by long-lasting severe impacts of aerial emissions of the copper-nickel smelter in Monchegorsk, northwestern Russia. We used pheromone traps to measure the population densities of this leafrolling moth and to collect specimens for assessment of three morphological stress indices: size, forewing melanization, and fluctuating asymmetry in wing venation. Wing length of E. ministrana increased by 10%, and neither forewing melanization nor fluctuating asymmetry changed from the unpolluted forest to the heavily polluted industrial barren. However, the population density of E. ministrana decreased 5 to 10 fold in the same pollution gradient. Thus, none of the studied potential morphological stress indicators signaled vulnerability of E. ministrana to environmental pollution and/or to pollution-induced environmental disturbance. We conclude that insect populations can decline without any visible signs of stress. The use of morphological proxies of insect fitness to predict the consequences of human impact on insect populations is therefore risky until causal relationships between these proxies and insect abundance are deciphered.

Plants and mycorrhizal symbionts acquire substantial soil nitrogen from gaseous ammonia transport

Nitrogen (N) is an essential nutrient that limits plant growth in many ecosystems. Here we investigate an overlooked component of the terrestrial N cycle - subsurface ammonia (NH₃ ) gas transport and its contribution to plant and mycorrhizal N acquisition. We used controlled mesocosms, soil incubations, stable isotopes, and imaging to investigate edaphic drivers of NH₃ gas efflux, track lateral subsurface N transport originating from ¹⁵ NH₃ gas or ¹⁵ N-enriched organic matter, and assess plant and mycorrhizal N assimilation from this gaseous transport pathway. NH₃ is released from soil organic matter, travels belowground, and contributes to root and fungal N content. Abiotic soil properties (pH and texture) influence the quantity of NH₃ available for subsurface transport. Mutualisms with arbuscular mycorrhizal (AM) fungi can substantially increase plant NH₃ -N uptake. The grass Brachypodium distachyon acquired 6-9% of total plant N from organic matter-N that traveled as a gas belowground. Colonization by the AM fungus Rhizophagus irregularis was associated with a two-fold increase in total plant N acquisition from subsurface NH₃ gas. NH₃ gas transport and uptake pathways may be fundamentally different from those of more commonly studied soil N species and warrant further research.

The good, the bad and the ugly of COVID-19 lockdown effects on wildlife conservation: Insights from the first European locked down country

The COVID-19 pandemic zoonosis has determined extensive lockdowns worldwide that provide an unprecedented opportunity to understand how large-scale shifts of human activities can impact wildlife. We addressed the impacts of the COVID-19 lockdown on wildlife in Italy, the first European country that performed a countrywide lockdown, and identified potentially beneficial and negative consequences for wildlife conservation and management. We combined a qualitative analysis of social media information with field data from multiple taxa, data from citizen science projects, and questionnaires addressed to managers of protected areas. Both social media information and field data suggest that a reduction of human disturbance allowed wildlife to exploit new habitats and increase daily activity. The field data confirmed some positive effects on wildlife conservation, such as an increase in species richness in temporarily less-disturbed habitats, a higher breeding success of an aerial insectivorous bird, and reduction of road-killing of both amphibians and reptiles. Despite some positive effects, our data also highlighted several negative impacts of the COVID-19 crisis on wildlife. The lower human disturbance linked to lockdown was in fact beneficial for invasive alien species. Results from questionnaires addressed to managers of protected areas highlighted that the COVID-19 lockdown interrupted actions for the control of invasive alien species, and hampered conservation activities targeting threatened taxa. Furthermore, the reduction of enforcement could cause a surge of illegal killing of wildlife. The COVID-19 crisis, besides having deep socio-economic impacts, might profoundly affect wildlife conservation, with potentially long-lasting effects.

Ecology and Evolution of Intraspecific Chemodiversity of Plants

An extraordinarily high intraspecific chemical diversity, i.e. chemodiversity, has been found in several plant species, of which some are of major ecological or economic relevance. Moreover, even within an individual plant there is substantial chemodiversity among tissues and across seasons. This chemodiversity likely has pronounced ecological effects on plant mutualists and antagonists, associated foodwebs and, ultimately, biodiversity. Surprisingly, studies on interactions between plants and their herbivores or pollinators often neglect plant chemistry as a level of diversity and phenotypic variation. The main aim of this Research Unit (RU) is to understand the emergence and maintenance of intraspecific chemodiversity in plants. We address the following central questions:

1) How does plant chemodiversity vary across levels, i.e., within individuals, among individuals within populations, and among populations?

2) What are the ecological consequences of intraspecific plant chemodiversity?

3) How is plant chemodiversity genetically determined and maintained?

By combining field and laboratory studies with metabolomics, transcriptomics, genetic tools, statistical data analysis and modelling, we aim to understand causes and consequences of plant chemodiversity and elucidate its impacts on the interactions of plants with their biotic environment. Furthermore, we want to identify general principles, which hold across different species, and develop meaningful measures to describe the fascinating diversity of defence chemicals in plants. These tasks require integrated scientific collaboration of experts in experimental and theoretical ecology, including chemical and molecular ecology, (bio)chemistry and evolution.

Nitric Oxide, an Essential Intermediate in the Plant-Herbivore Interaction

Reactive nitrogen species (RNS), mainly nitric oxide (NO), are highly reactive molecules with a prominent role in plant response to numerous stresses including herbivores, although the information is still very limited. This perspective article compiles the current progress in determining the NO function, as either a signal molecule, a metabolic intermediate, or a toxic oxidative product, as well as the contribution of molecules associated with NO metabolic pathway in the generation of plant defenses against phytophagous arthropods, in particular to insects and acari.