Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

Background Aboveground, plants release volatile organic compounds (VOCs) that act as chemical signals between neighbouring plants. It is now well documented that VOCs emitted by the roots in the plant rhizosphere also play important ecological roles in the soil ecosystem, notably in plant defence because they are involved in interactions between plants, phytophagous pests and organisms of the third trophic level. The roles played by root-emitted VOCs in between- and within-plant signalling, however, are still poorly documented in the scientific literature. Scope Given that (1) plants release volatile cues mediating plant-plant interactions aboveground, (2) roots can detect the chemical signals originating from their neighbours, and (3) roots release VOCs involved in biotic interactions belowground, the aim of this paper is to discuss the roles of VOCs in between- and within-plant signalling belowground. We also highlight the technical challenges associated with the analysis of root-emitted VOCs and the design of experiments targeting volatile-mediated root-root interactions. Conclusions We conclude that root-root interactions mediated by volatile cues deserve more research attention and that both the analytical tools and methods developed to study the ecological roles played by VOCs in interplant signalling aboveground can be adapted to focus on the roles played by root-emitted VOCs in between- and within-plant signalling

Use of molecular dynamics simulations to study the interactions between barley allelochemicals and plant plasma membrane

Gramine and hordenine, two alkaloids produced by barley, were shown to inhibit the growth of a common weed (Matricaria recutita L.). This feature could be useful in order to reach a more sustainable weeds management. In vitro experiments have proven that both molecules do interact with lipid bilayers (made of a phosphatidylglycerol (PG) lipid) mimicking plant plasma membranes and are able to modify some of their properties. Moreover, gramine was shown to be more effective than hordenine in both inhibiting weeds growth and altering lipid bilayers properties, suggesting that interactions with membranes could be linked to their mode of action. Molecular dynamics (MD) simulations are carried out in order to get an insight into the molecular mechanisms that underlie these interactions with model membranes and to discriminate between gramine behavior and hordenine behavior

Plasticité developpementale de Brachypodium distachyon en réponse à la déficience en phosphore: modulation par inoculation de bactéries solubilisatrices du phosphate

peer reviewedMineral phosphorus (P) fertilisers must be used wisely in order to preserve rock phosphate, a limited and non-renewable resource. The use of bio-inoculants to improve soil nutrient availability and trigger an efficient plant response to nutrient deficiency is one potential strategy in the attempt to decrease P inputs in agriculture. An in vitro co-cultivation system was used to study the response of Brachypodium distachyon to contrasted P supplies (soluble and poorly soluble forms of P) and inoculation with P solubilizing bacteria. Brachypodium's responses to P conditions and inoculation with bacteria were studied in terms of developmental plasticity and P use efficiency. Brachypodium showed plasticity in its biomass allocation pattern in response to variable P conditions, specifically by prioritizing root development over shoot productivity under poorly soluble P conditions. Despite the ability of the bacteria to solubilize P, shoot productivity was depressed in plants inoculated with bacteria, although the root system development was maintained. The negative impact of bacteria on biomass production in Brachypodium might be attributed to inadequate C supply to bacteria, an increased competition for P between both organisms under P-limiting conditions, or an accumulation of toxic bacterial metabolites in our cultivation system. Both P and inoculation treatments impacted root system morphology. The modulation of Brachypodium’s developmental response to P supplies by P solubilizing bacteria did not lead to improved P use efficiency. Our results support the hypothesis that plastic responses of Brachypodium cultivated under P-limited conditions are modulated by P solubilizing bacteria. The considered experimental context impacts plant–bacteria interactions. Choosing experimental conditions as close as possible to real ones is important in the selection of P solubilizing bacteria. Both persistent homology and allometric analyses proved to be useful tools that should be considered when studying the impact of bio-inoculants on plant development in response to varying nutritional context

Soil chemical legacies trigger species‐specific and context‐dependent root responses in later arriving plants

Abstract Soil legacies play an important role for the creation of priority effects. However, we still poorly understand to what extent the metabolome found in the soil solution of a plant community is conditioned by its species composition and whether soil chemical legacies affect subsequent species during assembly. To test these hypotheses, we collected soil solutions from forb or grass communities and evaluated how the metabolome of these soil solutions affected the growth, biomass allocation and functional traits of a forb ( Dianthus deltoides ) and a grass species ( Festuca rubra ). Results showed that the metabolomes found in the soil solutions of forb and grass communities differed in composition and chemical diversity. While soil chemical legacies did not have any effect on F . rubra , root foraging by D . deltoides decreased when plants received the soil solution from a grass or a forb community. Structural equation modelling showed that reduced soil exploration by D . deltoides arose via either a root growth‐dependent pathway (forb metabolome) or a root trait‐dependent pathway (grass metabolome). Reduced root foraging was not connected to a decrease in total N uptake. Our findings reveal that soil chemical legacies can create belowground priority effects by affecting root foraging in later arriving plants

Toward a Comprehensive and Integrated Strategy of the European Marine Research Infrastructures for Ocean Observations

Research Infrastructures (RIs) are large-scale facilities encompassing instruments, resources, data and services used by the scientific community to conduct high-level research in their respective fields. The development and integration of marine environmental RIs as European Research Vessel Operators [ERVO] (2020) is the response of the European Commission (EC) to global marine challenges through research, technological development and innovation. These infrastructures (EMSO ERIC, Euro-Argo ERIC, ICOS-ERIC Marine, LifeWatch ERIC, and EMBRC-ERIC) include specialized vessels, fixed-point monitoring systems, Lagrangian floats, test facilities, genomics observatories, bio-sensing, and Virtual Research Environments (VREs), among others. Marine ecosystems are vital for life on Earth. Global climate change is progressing rapidly, and geo-hazards, such as earthquakes, volcanic eruptions, and tsunamis, cause large losses of human life and have massive worldwide socio-economic impacts. Enhancing our marine environmental monitoring and prediction capabilities will increase our ability to respond adequately to major challenges and efficiently. Collaboration among European marine RIs aligns with and has contributed to the OceanObs’19 Conference statement and the objectives of the UN Decade of Ocean Science for Sustainable Development (2021–2030). This collaboration actively participates and supports concrete actions to increase the quality and quantity of more integrated and sustained observations in the ocean worldwide. From an innovation perspective, the next decade will increasingly count on marine RIs to support the development of new technologies and their validation in the field, increasing market uptake and produce a shift in observing capabilities and strategies.Peer reviewe

Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

peer reviewedBackground Aboveground, plants release volatile organic compounds (VOCs) that act as chemical signals between neighbouring plants. It is now well documented that VOCs emitted by the roots in the plant rhizosphere also play important ecological roles in the soil ecosystem, notably in plant defence because they are involved in interactions between plants, phytophagous pests and organisms of the third trophic level. The roles played by root-emitted VOCs in between- and within-plant signalling, however, are still poorly documented in the scientific literature. Scope Given that (1) plants release volatile cues mediating plant-plant interactions aboveground, (2) roots can detect the chemical signals originating from their neighbours, and (3) roots release VOCs involved in biotic interactions belowground, the aim of this paper is to discuss the roles of VOCs in between- and within-plant signalling belowground. We also highlight the technical challenges associated with the analysis of root-emitted VOCs and the design of experiments targeting volatile-mediated root-root interactions. Conclusions We conclude that root-root interactions mediated by volatile cues deserve more research attention and that both the analytical tools and methods developed to study the ecological roles played by VOCs in interplant signalling aboveground can be adapted to focus on the roles played by root-emitted VOCs in between- and within-plant signalling

Root-emitted volatile organic compounds in belowground plant-plant interactions

Plants are able to synthesise and release volatile organic compounds (VOCs) aboveground (leaves, stems, flowers and fruits) and belowground (roots). Once emitted, these molecules are key mediators in biotic interactions as they can be perceived by plant neighbours (first trophic level) and are able to attract/repel organisms of the second (insect herbivores, plant parasitic nematodes) or the third trophic level (entomopathogenic nematodes, parasitoids, etc.). Although many laboratory and field experiments have focused on VOC-mediated plant-plant interactions aboveground, less is known regarding the roles played by root-emitted VOCs in between- and within-plant signalling. In this context, the main goals of this PhD thesis were to (1) identify and quantify the VOCs emitted by barley and chamomile roots and (2) study the influence of chamomile root volatiles on the growth (biomass production and allocation) and the root system architecture (RSA) of barley (interspecific model). Root-emitted VOCs were analysed without extracting the roots from the soil (in situ) using a three-step gas chromatography-mass spectrometry methodology. Plant-plant interaction bioassays were performed using an original experimental device allowing the controlled exposition of growing barley roots to the volatile compounds emitted by chamomile roots for 15 days. In order to speed up the RSA analysis of recipient barley plants, we developed an R package (archiDART) allowing (1) the batch processing of the raw data exported by Data Analysis of Root Tracings (DART) and root image analysis software tools supporting the Root System Markup Language (RSML) format, and (2) the automated computation of RSA traits. Our results showed that crushed barley roots produced mainly hexanal, (E)-hex-2-enal, (E)-non-2-enal and (E,Z)-nona-2,6-dienal. Three-day-old seminal roots were characterised by higher total and individual VOC concentrations compared with older phenological stages. Our experiments also showed that enzymatic activities were required for volatile production. For each developmental stage, the lipoxygenase (LOX) specificity was greater for linoleic acid than for α-linolenic acid. The greatest LOX activities using linoleic and α-linolenic acids as substrates were measured in 7- and 3-day-old roots, respectively. Although undamaged barley roots did not release detectable amounts of VOCs, the analysis of VOCs emitted by mechanically injured roots showed that (E)-non-2-enal (13.8 ± 4.9 ng/g dry wt/h) and (E,Z)-nona-2,6-dienal (4.7 ± 1.8 ng/g dry wt/h) were the only VOCs detected in the plant rhizosphere. Contrasting with these results, the undamaged roots of 61- to 78-day-old chamomile plantlets released mainly one trinorsesquiterpene (albene) and four tricyclic sesquiterpene hydrocarbons (silphinene, modheph-2-ene, α-isocomene and β-isocomene) associated with the Asteraceae family. For each sesquiterpene hydrocarbon, the emission rate was positively correlated with plant age. Based on these results, we performed plant-plant interaction bioassays to investigate the roles played by chamomile root volatiles on the growth and RSA of barley. After 15 days of exposure, plants exposed to the volatiles emitted by the soil and chamomile roots or by the soil alone (control) were morphologically similar. Although not statistically significant (P < 0.09), the leaf area and the total seminal root length were the only parameters that tended to be greater in plants that received the volatile compounds emitted by chamomile roots compared with control plantlets. All these results are discussed in the context of belowground chemical ecology. In addition, some improvements of the experimental devices developed in this research project are also suggested at the end of this PhD thesis

Modelling of growth in barley (Hordeum distichon L.) and the Poaceae model Brachypodium distachyon (L.) Beauv. and root content analysis of volatile organic compounds in barley

RHIZOVO

Barley (Hordeum distichon L.) roots synthesise volatile aldehydes with a strong age-dependent pattern and release (E)- non-2-enal and (E,Z)-nona-2,6-dienal after mechanical injury

In the context of chemical ecology, the analysis of the temporal production pattern of volatile organic compounds (VOCs) in root tissues and the emission rate measurement of root-emitted VOCs are of major importance for setting up experiments to study the implication of these compounds in biotic interactions. Such analyses, however, remain challenging because of the belowground location of plant root systems. In this context, this study describes the evolution of the root VOC production pattern of barley (Hordeum distichon L.) at five developmental stages from germination to the end of tillering and evaluates the emission of the identified VOCs in an artificial soil. VOCs produced by crushed root tissues and released by unexcavated root systems were analysed using dynamic sampling devices coupled to a gas chromatography-mass spectrometry methodology (synchronous SCAN/SIM). The results showed that, at each analysed developmental stage, crushed barley roots produced mainly four volatile aldehydes: hexanal; (E)-hex-2-enal; (E)-non-2-enal; and (E,Z)-nona-2,6-dienal. Higher total and individual VOC concentrations were measured in 3-day-old seminal roots compared with older phenological stages. For each developmental stage, the lipoxygenase (LOX) activity was greater for linoleic acid than α-linolenic acid and the greatest LOX activities using linoleic and α- linolenic acids as substrates were measured in 7- and 3-day-old roots, respectively. The analysis of VOCs released by barley roots into the soil showed that (E)-non-2- enal and (E,Z)-nona-2,6-dienal were the only VOCs emitted in quantifiable amounts by mechanically injured roots