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Volatile cues can induce and/or prime plant defences, but it is less well known if plants also respond by altering growth and reproduction‐related parameters.Here, we evaluated whether plant volatile cues can elicit changes in growth, flower production, net photosynthesis rate and defences in receiver plants and whether those responses are similar to those elicited in response to direct herbivore‐feeding.Our results demonstrate that exposure to volatiles emitted from damaged neighbours accelerated the time to first flowering, increased the number of flowers produced and the net photosynthesis rate, but did not alter the fresh harvested plant biomass and volatile defences, compared to non‐exposed plants. Earlier flowering was also observed for plants exposed to volatiles from undamaged plants.These responses differed from those of plants exposed to actual herbivore‐feeding for which feeding enhanced net photosynthesis rate but reduced growth and had no effect on reproduction and defence in response to subsequent herbivory.Synthesis. These findings document that plant airborne cues can influence floral traits of receiver plants. In particular, the flower phenology is modulated, and photosynthesis is enhanced, suggesting that carbon allocation could be directed toward reproduction. [ABSTRACT FROM AUTHOR]

Air pollutants—such as nitrogen oxides, emitted in diesel exhaust, and ozone (O3)—disrupt interactions between plants, the insect herbivore pests that feed upon them and natural enemies of those herbivores (e.g. parasitoids). Using eight field-based rings that emit regulated quantities of diesel exhaust and O3, we investigated how both pollutants, individually and in combination, altered the attraction and parasitism rate of a specialist parasitoid (Diaeretiella rapae) on aphid-infested and un-infested Brassica napus plants. Individual effects of O3 decreased D. rapae abundance and emergence by 37% and 55%, respectively, compared with ambient (control) conditions. When O3 and diesel exhaust were emitted concomitantly, D. rapae abundance and emergence increased by 79% and 181%, respectively, relative to control conditions. This attraction response occurred regardless of whether plants were infested with aphids and was associated with an increase in the concentration of aliphatic glucosinolates, especially gluconapin (3-butenyl-glucosinolate), within B. napus leaves. Plant defensive responses and their ability to attract natural aphid enemies may be beneficially impacted by pollution exposure. These results demonstrate the importance of incorporating multiple air pollutants when considering the effects of air pollution on plant–insect interactions. [ABSTRACT FROM AUTHOR]

Soil microbiota can either slow down or facilitate plant invasions through their effects on plant performance. Associations with soil microbiota can also modify other plant traits such as herbivore resistance, which can indirectly affect the outcome of plant introductions.We studied the effects of soil microbiota on the perennial herbaceous legume Lupinus polyphyllus that hosts nitrogen‐fixing mutualistic bacteria. We compared the plant performance, herbivore resistance and volatile organic compounds (VOCs) of plants from native (North American) and invasive (Finnish) populations of the species that were inoculated with intact or autoclaved soil from an invasive population.We found that plants of both origins greatly benefited from the intact soil inoculum with respect to all performance measures considered, suggesting that beneficial nitrogen‐fixing rhizobia in the soil play a major role in shaping plant phenotypes. For three traits, effects of the intact soil inoculum were stronger in plants of native origin than in plants of invasive origin (number of leaves, herbivore resistance and total biomass). With the intact soil inoculum, plants of invasive origin were more resistant to snails than plants of native origin. Strikingly, differences in resistance to snails between plants of different origins disappeared entirely when soil microbes were reduced. Soil inoculum treatment altered the composition of the leaf VOC bouquet similarly regardless of plant origin.Synthesis. These results demonstrate the ability of Lupinus polyphyllus to associate with and benefit from putatively novel soil microbiota including rhizobia, which has likely contributed to its invasion success. Furthermore, it appears that the invasive populations have adapted to be less reliant on their symbionts, which further facilitates species spread. To our knowledge, this is the first study to demonstrate that differences in herbivore resistance between native and invasive plant populations of the same species can depend entirely on soil microbiota. [ABSTRACT FROM AUTHOR]

Conifers are dominant tree species in boreal forests, but are susceptible to attack by bark beetles. Upon bark beetle attack, conifers release substantial quantities of volatile organic compounds known as herbivore-induced plant volatiles (HIPVs). Earlier studies of broadleaved plants have shown that HIPVs provide information to neighbouring plants, which may enhance their defences. However, the defence responses of HIPV-receiver plants have not been described for conifers. Here we advance knowledge of plant–plant communication in conifers by documenting a suite of receiver-plant responses to bark-feeding-induced volatiles. Scots pine seedlings exposed to HIPVs were more resistant to subsequent weevil feeding and received less damage. Receiver plants had both induced and primed volatile emissions and their resin ducts had an increased epithelial cell (EC) mean area and an increased number of cells located in the second EC layer. Importantly, HIPV exposure increased stomatal conductance and net photosynthesis rate of receiver plants. Receiver-plant responses were also examined under elevated ozone conditions and found to be significantly altered. However, the final defence outcome was not affected. These findings demonstrate that HIPVs modulate conifer metabolism through responses spanning photosynthesis and chemical defence. The responses are adjusted under ozone stress, but the defence benefits remain intact. [ABSTRACT FROM AUTHOR]

The intensification of summer drought expected with climate change can induce metabolism modifications in plants to face such constraints. In this experiment, we used both a targeted approach focused on flavonoids, as well as an untargeted approach, to study a broader fraction of the leaf metabolome of Quercus pubescens exposed to amplified drought. A forest site equipped with a rainfall exclusion device allowed reduction of natural rainfall by ~30% over the tree canopy. Leaves of natural drought (ND) and amplified drought (AD) plots were collected over three seasonal cycles (spring, summer, and autumn) in 2013 (the second year of rain exclusion), 2014, and 2015. As expected, Q. pubescens metabolome followed a seasonal course. In the summer of 2015, the leaf metabolome presented a shifted and early autumnal pattern because of harsher conditions during this year. Despite low metabolic modification at the global scale, our results demonstrated that 75% of Quercus metabolites were upregulated in springs when trees were exposed to AD, whereas 60 to 73% of metabolites (93% in summer 2015), such as kaempferols and quercetins, were downregulated in summers/autumns. Juglanin, a kaempferol pentoside, as well as rhododendrin derivatives, were upregulated throughout the year, suggesting an antioxidant ability of these metabolites. Those changes in terms of phenology and leaf chemistry could, in the end, affect the ecosystem functioning. [ABSTRACT FROM AUTHOR]

This review highlights the importance of volatile organic compounds (VOCs) in plant–plant interactions, covering the defence, growth, and reproduction responses in recipient plants upon VOC exposure. It is firmly established that plants respond to biotic and abiotic stimuli by emitting volatile organic compounds (VOCs). These VOCs provide information on the physiological status of the emitter plant and are available for detection by the whole community. In the context of plant–plant interactions, research has focused mostly on the defence-related responses of receiver plants. However, responses may span hormone signalling and both primary and secondary metabolism, and ultimately affect plant fitness. Here we present a synthesis of plant–plant interactions, focusing on the effects of VOC exposure on receiver plants. An overview of the important chemical cues, the uptake and conversion of VOCs, and the adsorption of VOCs to plant surfaces is presented. This is followed by a review of the substantial VOC-induced changes to receiver plants affecting both primary and secondary metabolism and influencing plant growth and reproduction. Further research should consider whole-plant responses for the effective evaluation of the mechanisms and fitness consequences of exposure of the receiver plant to VOCs. [ABSTRACT FROM AUTHOR]

Plant-to-plant volatile-mediated communication and subsequent induced resistance to insect herbivores is common. Less clear is the adaptive significance of these interactions; what selective mechanisms favour plant communication and what conditions allow individuals to benefit by both emitting and responding to cues? We explored the predictions of two non-exclusive hypotheses to explain why plants might emit cues, the kin selection hypothesis (KSH) and the mutual benefit hypothesis (MBH). We examined 15 populations of sagebrush that experience a range of naturally occurring herbivory along a 300 km latitudinal transect. As predicted by the KSH, we found several uncommon chemotypes with some chemotypes occurring only within a single population. Consistent with the MBH, chemotypic diversity was negatively correlated with herbivore pressure; sites with higher levels of herbivory were associated with a few common cues broadly recognized by most individuals. These cues varied among different populations. Our results are similar to those reported for anti-predator signalling in vertebrates. [ABSTRACT FROM AUTHOR]

Plants respond to damage by herbivores or to reliable cues of damage by changing in ways that provide greater resistance and increase their fitness. Sagebrush has been a model system for understanding induced resistance, although resistance in this system is commonly assessed by quantifying damage at the end of the season; this measure is slow and lacks accuracy and interpretability because so many other factors also affect levels of damage. Herbivore choice offers a potentially rapid and accurate alternative assay of induced resistance. Here we evaluate whether feeding behavior of a specialized Chrysomelid beetle, Trirhabda pilosa, could be used to assay induced changes in plant quality. Beetle larvae were offered the choice between two leaves in Petri dish arenas. We found that beetles avoided leaves that were naturally damaged by herbivores, experimentally clipped with scissors, and exposed to the volatiles from naturally or experimentally damaged neighboring leaves compared to control leaves. Experiments varied the source of the damage, the duration of the feeding test, and how damage was measured, still, beetles consistently preferred uninduced controls by a 2:1 ratio over leaves exposed to cues of damage. These results suggest that behavioral assays using T. pilosa larvae can be used to rapidly evaluate induced resistance in this system. More generally, movement and feeding behaviors of herbivores are an important and underappreciated component of induced plant responses. [ABSTRACT FROM AUTHOR]

Sublethal stimulation and hormetic responses are increasingly identified and acknowledged in scientific research. However, the occurrence and characteristics of such responses in insect vectors of pathogens are little explored and poorly understood. Here, we collate significant evidence from the scientific literature showing that sublethal doses of environmental contaminants, such as pesticides, microplastics, and plasticizers, induce stimulation and hormetic responses in insect vectors of pathogens of agricultural and public health importance, including mosquitoes, other dipterans, psyllids, aphids, and planthoppers. Physiological, behavioral, and demographic traits can be enhanced by exposure to lower subtoxic contaminant doses while being inhibited by higher toxic doses. Energetic trade-offs can also occur, especially at sublethal doses higher than the no-observed-adverse-effect level (NOAEL). The relevant literature is limited and so are the number of doses commonly included in the studies, precluding firm conclusions and enhanced understanding. Nevertheless, these effects are significant and could undermine human and environmental health, and thus sustainability agendas, if ultimately the transmission of pathogens and disease spread and severity are increased. Further research is urgently needed to tackle these phenomena, especially under field conditions. The findings discussed here are relevant to chemical risk assessment and chemical safety evaluations, in which all possible effects from the lowest to higher doses should be considered. [Display omitted] • Sublethal contaminant doses stimulate pathogen vectors and cause hormesis. • Stimulation was observed in vectors of agricultural and public health importance. • Pesticides, microplastics and plasticizers can cause stimulation and hormesis. • Effects can persist or fluctuate across generations. • Chemical risk assessment should be improved to account for these responses. [ABSTRACT FROM AUTHOR]