Mediation of Impacts of Elevated CO2 and Light Environment on Arabidopsis thaliana (L.) Chemical Defense against Insect Herbivory Via Photosynthesis

Regional variation in the antibacterial activity of a wild plant, wild garlic (Allium ursinum L.)

Antibacterial activity is a common and highly studied property of plant secondary metabolites. Despite the extensive literature focusing on identifying novel antibacterial metabolites, little work has been undertaken to examine variation in levels of antibacterial activity in any plant species. Here, we used large-scale sampling of leaves of the antibacterial plant, wild garlic (Allium ursinum L.), assembling a set of tissue extracts from 168 plants, with 504 leaves collected and analysed. We assayed extracts for antibacterial activity against Bacillus subtilis and used LC-MS to carry out a chemometric analysis examining variation in individual metabolites, comparing them with several ecological parameters. We found that allicin was the only metabolite which was positively related to antibacterial activity. Soil temperature was a key determinant of variability in the concentrations of many foliar metabolites, however, neither allicin concentrations nor antibacterial activity was related to any of our measured ecological parameters, other than roadside proximity. We suggest that the synthesis of allicin precursors may be largely independent of growing conditions. This may be to ensure that allicin is synthesised rapidly and in sufficiently high concentrations to effectively prevent herbivory and pest damage. This finding contrasts with flavonoids which were found to vary greatly between plants and across sites. Our findings suggest that key biologically active metabolites are constrained in their concentration range compared to other compounds in the metabolome. This has important implications for the development of wild garlic as a health supplement or animal feed additive.

Salicylic acid and jasmonic acid in elevated CO2-induced plant defense response to pathogens

Plants respond to elevated CO₂ (eCO₂) via a variety of signaling pathways that often rely on plant hormones. In particular, phytohormone salicylic acid (SA) and jasmonic acid (JA) play a key role in plant defense against diverse pathogens at eCO₂. eCO₂ affects the synthesis and signaling of SA and/or JA and variations in SA and JA signaling lead to variations in plant defense responses to pathogens. In general, eCO₂ promotes SA signaling and represses the JA pathway, and thus diseases caused by biotrophic and hemibiotrophic pathogens are typically suppressed, while the incidence and severity of diseases caused by necrotrophic fungal pathogens are enhanced under eCO₂ conditions. Moreover, eCO₂-induced modulation of antagonism between SA and JA leads to altered plant immunity to different pathogens. Notably, research in this area has often yielded contradictory findings and these responses vary depending on plant species, growth conditions, photoperiod, and fertilizer management. In this review, we focus on the recent advances in SA, and JA signaling pathways in plant defense and their involvement in plant immune responses to pathogens under eCO₂. Since atmospheric CO₂ will continue to increase, it is crucial to further explore how eCO₂ may alter plant defense and host-pathogen interactions in the context of climate change in both natural as well as agricultural ecosystems.

Ontogeny-dependent effects of elevated CO2 and watering frequency on interaction between Aristolochia contorta and its herbivores

Effects of environmental change on plants can differ due to sequential changes in their life-history strategies (i.e., ontogenetic variations). The fitness of herbivorous insects by physiological changes of the host plant could be affected depending on their diet breadth. However, little is known regarding the combinational effects of plant ontogeny and climate change on plant-herbivore interactions. This study examined the plant ontogeny-dependent effects of climate change on the interaction between a host plant (Aristolochia contorta), its specialist herbivore (Sericinus montela), and a generalist herbivore (Spodoptera exigua). Plants were grown under a factorial design of two distinct CO₂ concentrations (ambient, 400 ppm; elevated, 560 ppm) and two watering frequencies (control, once a week; increased, twice a week). Plant ontogeny ameliorated the effects of climate change by altering its defensive traits, where nutrient-related factors were cumulatively affected by climate change. Herbivore performance was assessed at three different plant ontogenetic stages (1st-year juvenile, 1st-year senescence, and 2nd-year juvenile). Elevated CO₂ levels reduced the growth and survival of the specialist herbivore, whereas increased watering frequency partially alleviated this reduced performance. Generalist herbivore performance slightly increased under elevated CO₂ levels with progressing ontogenetic stages. The effects of climate change, both elevated CO₂ and increased watering frequency were weaker in 2nd-year juveniles than in 1st-year juveniles. Elevated CO₂ levels detrimentally affected the nutritional quality of A. contorta leaves. The effects of climate change on both specialist and generalist herbivore performance differed as plant ontogenetic stage proceeded. Increased growth rates and survival of the generalist herbivore at the latter ontogenetic stage might negatively affect the population dynamics of a specialist herbivore. This study suggests that biases are possible when the plant-herbivore interaction under a changing environment is predicted from a singular plant ontogenetic stage.

Impact of Future Elevated Carbon Dioxide on C3 Plant Resistance to Biotic Stresses

Before the end of the century, atmospheric carbon dioxide levels are predicted to increase to approximately 900 ppm. This will dramatically affect plant physiology and influence environmental interactions and, in particular, plant resistance to biotic stresses. This review is a broad survey of the current research on the effects of elevated CO₂ (eCO₂) on phytohormone-mediated resistance of C₃ agricultural crops and related model species to pathogens and insect herbivores. In general, while plants grown in eCO₂ often have increased constitutive and induced salicylic acid levels and suppressed induced jasmonate levels, there are exceptions that implicate other environmental factors, such as light and nitrogen fertilization in modulating these responses. Therefore, this review sets the stage for future studies to delve into understanding the mechanistic basis behind how eCO₂ will affect plant defensive phytohormone signaling pathways under future predicted environmental conditions that could threaten global food security to inform the best agricultural management practices.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Elevated CO2 aggravates invasive thrip damage by altering its host plant nutrient and secondary metabolism

As atmospheric CO₂ concentration continues to increase, plants using CO₂ as raw materials for photosynthesis will inevitably be affected, which in turn affects the life history and behavior of herbivorous insects. Our previous research has shown increased food intake and aggravated damage of western flower thrips, Frankliniella occidentalis to kidney bean (Phaseolus vulgaris) caused by elevated CO₂ (eCO₂), however the molecular mechanism of this phenomenon is unclear. In this study, the comparative transcriptome analysis combined with corresponding phenotypic changes were studied to reveal the molecular mechanism of interaction between F. occidentalis and P. vulgaris under eCO₂. Inferred from the results, eCO₂ had different degrees of inhibition to the defense responses caused by thrips infestation in P. vulgaris leaf sap based on nutrients, plant hormones and secondary metabolites, making P. vulgaris leaves less resistant to thrips under eCO₂ compared to ambient CO₂ (aCO₂). Besides, the contents of glucose, trehalose, triglycerides and free fatty acids in F. occidentalis adults increased significantly after feeding on the P. vulgaris leaf sap with significantly increased soluble sugars content under eCO₂, which might lead to glucolipid metabolic disorders and increased food intake of F. occidentalis adults. The results indicated that decreased plant defense of P. vulgaris and increased food intake of F. occidentalis adults were combined to aggravate the thrips damage under eCO₂, providing a theoretical basis for future occurrence trend of thrips under eCO₂.

Effects of elevated CO2 on resistant and susceptible rice cultivar and its primary host, brown planthopper (BPH), Nilaparvata lugens (Stål)

The elevated CO2 (eCO2) has positive response on plant growth and negative response on insect pests. As a contemplation, the feeding pattern of the brown plant hopper, Nilaparvata lugens Stål on susceptible and resistant rice cultivars and their growth rates exposed to eCO2 conditions were analyzed. The eCO2 treatment showed significant differences in percentage of emergence and rice biomass that were consistent across the rice cultivars, when compared to the ambient conditions. Similarly, increase in carbon and decrese in nitrogen ratio of leaves and alterations in defensive peroxidase enzyme levels were observed, but was non-linear among the cultivars tested. Lower survivorship and nutritional indices of N. lugens were observed in conditions of eCO2 levels over ambient conditions. Results were nonlinear in manner. We conclude that the plant carbon accumulation increased due to eCO2, causing physiological changes that decreased nitrogen content. Similarly, eCO2 increased insect feeding, and did alter other variables such as their biology or reproduction.

Biocontrol of invasive weeds under climate change: progress, challenges and management implications

Climate change is predicted to increase the frequency and impact of plant invasions, creating a need for new control strategies as part of mitigation planning. The complex interactions between invasive plants and biocontrol agents have created distinct policy and management challenges, including the effectiveness and risk assessment of biocontrol under different climate change scenarios. In this brief review, we synthesize recent studies describing the potential ecological and evolutionary outcomes for biocontrol agents/candidates for plant invaders under climate change. We also discuss potential methodologies that can be used as a framework for predicting ecological and evolutionary responses of plant-natural enemy interactions under climate change, and for refining our understanding of the efficacy and risk of using biocontrol on invasive plants.

Fertilizer Rate-Associated Increase in Foliar Jasmonate Burst Observed in Wounded Arabidopsis thaliana Leaves is Attenuated at eCO2

The predicted future increase in tropospheric carbon dioxide (CO2) levels will have major effects on C3 plants and their interactions with other organisms in the biosphere. In response to attack by chewing arthropod herbivores or nectrotrophic pathogens, many plants mount a rapid and intense increase in jasmonate-related phytohormones that results in a robust defense response; however, previous studies have shown that C3 plants grown at elevated CO2 may have lower induced jasmonate levels, particularly in well nitrate-fertilized plants. Given the relationship between atmospheric CO2, photorespiration, cellular reductant and redox status, nitrogen assimilation and phytohormones, we compared wound-induced responses of the C3 plant Arabidopsis thaliana. These plants were fertilized at two different rates (1 or 10 mM) with nitrate or ammonium and grown at ambient or elevated CO2. In response to artificial wounding, an increase in cellular oxidative status leads to a strong increase in jasmonate phytohormones. At ambient CO2, increased oxidative state of nitrate-fertilized plants leads to a robust 7-iso-jasmonyl-L-isoleucine increase; however, the strong fertilizer rate-associated increase is alleviated in plants grown at elevated CO2. As well, the changes in ascorbate in response to wounding and wound-induced salicylic acid levels may also contribute to the suppression of the jasmonate burst. Understanding the mechanism underlying the attenuation of the jasmonate burst at elevated CO2 has important implications for fertilization strategies under future predicted climatic conditions.