Plant behavioural ecology: dynamic plasticity in secondary metabolites

Phenolic concentrations and carbon/nitrogen ratio in annual shoots of bilberry (Vaccinium myrtillus) after simulated herbivory

Herbivory can be reduced by the production of defense compounds (secondary metabolites), but generally defenses are costly, and growth is prioritized over defense. While defense compounds may deter herbivory, nutrients may promote it. In a field study in boreal forest in Norway, we investigated how simulated herbivory affected concentrations of phenolics (generally a defense) and the carbon/nitrogen (C/N) ratio in annual shoots of bilberry (Vaccinium myrtillus), a deciduous clonal dwarf shrub whose vegetative and generative parts provide forage for many boreal forest animals. We measured concentrations of total tannins, individual phenolics, nitrogen and carbon following several types and intensities of herbivory. We identified 22 phenolics: 15 flavonoids, 1 hydroquinone and 6 phenolic acids. After high levels of herbivory, the total tannin concentration and the concentration of these 22 phenolics together (called total phenolic concentration) were significantly lower in bilberry annual shoots than in the control (natural herbivory at low to intermediate levels). Low-intensive herbivory, including severe defoliation, gave no significantly different total tannin or total phenolic concentration compared with the control. Many individual phenolics followed this pattern, while phenolic acids (deterring insect herbivory) showed little response to the treatments: their concentrations were maintained after both low-intensive and severe herbivory. Contrary to our predictions, we found no significant difference in C/N ratio between treatments. Neither the Carbon:Nutrient Balance hypothesis nor the Optimal Defense hypotheses, theories predicting plant resource allocation to secondary compounds, can be used to predict changes in phenolic concentrations (including total tannin concentration) in bilberry annual shoots after herbivory: in this situation, carbon is primarily used for other functions (e.g., maintenance, growth, reproduction) than defense.

A trait-based framework linking the soil metabolome to plant-soil feedbacks

By modifying the biotic and abiotic properties of the soil, plants create soil legacies that can affect vegetation dynamics through plant-soil feedbacks (PSF). PSF are generally attributed to reciprocal effects of plants and soil biota, but these interactions can also drive changes in the identity, diversity and abundance of soil metabolites, leading to more or less persistent soil chemical legacies whose role in mediating PSF has rarely been considered. These chemical legacies may interact with microbial or nutrient legacies to affect species coexistence. Given the ecological importance of chemical interactions between plants and other organisms, a better understanding of soil chemical legacies is needed in community ecology. In this Viewpoint, we aim to: highlight the importance of belowground chemical interactions for PSF; define and integrate soil chemical legacies into PSF research by clarifying how the soil metabolome can contribute to PSF; discuss how functional traits can help predict these plant-soil interactions; propose an experimental approach to quantify plant responses to the soil solution metabolome; and describe a testable framework relying on root economics and seed dispersal traits to predict how plant species affect the soil metabolome and how they could respond to soil chemical legacies.

Chemically Mediated Plant-Plant Interactions: Allelopathy and Allelobiosis

Plant-plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant-plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant-plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant-plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant-plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root-soil interactions and plant-soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant-plant interactions.

Effects of leaf herbivory and autumn seasonality on plant secondary metabolites: A meta-analysis

Plant secondary metabolites (PSMs) are produced by plants to overcome environmental challenges, both biotic and abiotic. We were interested in characterizing how autumn seasonality in temperate and subtropical climates affects overall PSM production in comparison to herbivory. Herbivory is commonly measured between spring to summer when plants have high resource availability and prioritize growth and reproduction. However, autumn seasonality also challenges plants as they cope with limited resources and prepare survival for winter. This suggests a potential gap in our understanding of how herbivory affects PSM production in autumn compared to spring/summer. Using meta-analysis, we recorded overall production of 22 different PSM subgroups from 58 published papers to calculate effect sizes from herbivory studies (absence to presence) and temperate to subtropical seasonal studies (summer to autumn), while considering other variables (e.g., plant type, increase in time since herbivory, temperature, and precipitation). We also compared production of five phenolic PSM subgroups - hydroxybenzoic acids, flavan-3-ols, flavonols, hydrolysable tannins, and condensed tannins. We wanted to detect a shared response across all PSMs and found that herbivory increased overall PSM production in herbaceous plants. Herbivory was also found to have a positive effect on individual PSM subgroups, such as flavonol production, while autumn seasonality was found to have a positive effect on flavan-3-ol and condensed tannin production. We discuss how these responses might stem from plants producing some PSMs constitutively, whereas others are induced only after herbivory, and how plants produce metabolites with higher costs only during seasons when other resources for growth and reproduction are less available, while other phenolic PSM subgroups serve more than one function for plants and such functions can be season dependent. The outcome of our meta-analysis is that autumn seasonality changes some PSM production differently from herbivory, and we see value in further investigating seasonality-herbivory interactions with plant chemical defense.

Emerging sensing, imaging, and computational technologies to scale nano-to macroscale rhizosphere dynamics - Review and research perspectives

The soil region influenced by plant roots, i.e., the rhizosphere, is one of the most complex biological habitats on Earth and significantly impacts global carbon flow and transformation. Understanding the structure and function of the rhizosphere is critically important for maintaining sustainable plant ecosystem services, designing engineered ecosystems for long-term soil carbon storage, and mitigating the effects of climate change. However, studying the biological and ecological processes and interactions in the rhizosphere requires advanced integrated technologies capable of decoding such a complex system at different scales. Here, we review how emerging approaches in sensing, imaging, and computational modeling can advance our understanding of the complex rhizosphere system. Particularly, we provide our perspectives and discuss future directions in developing in situ rhizosphere sensing technologies that could potentially correlate local-scale interactions to ecosystem scale impacts. We first review integrated multimodal imaging techniques for tracking inorganic elements and organic carbon flow at nano- to microscale in the rhizosphere, followed by a discussion on the use of synthetic soil and plant habitats that bridge laboratory-to-field studies on the rhizosphere processes. We then describe applications of genetically encoded biosensors in monitoring nutrient and chemical exchanges in the rhizosphere, and the novel nanotechnology-mediated delivery approaches for introducing biosensors into the root tissues. Next, we review the recent progress and express our vision on field-deployable sensing technologies such as planar optodes for quantifying the distribution of chemical and analyte gradients in the rhizosphere under field conditions. Moreover, we provide perspectives on the challenges of linking complex rhizosphere interactions to ecosystem sensing for detecting biological traits across scales, which arguably requires using the best-available model predictions including the model-experiment and image-based modeling approaches. Experimental platforms relevant to field conditions like SMART (Sensors at Mesoscales with Advanced Remote Telemetry) soils testbed, coupled with ecosystem sensing and predictive models, can be effective tools to explore coupled ecosystem behavior and responses to environmental perturbations. Finally, we envision that with the advent of novel high-resolution imaging capabilities at nano- to macroscale, and remote biosensing technologies, combined with advanced computational models, future studies will lead to detection and upscaling of rhizosphere processes toward ecosystem and global predictions.

Variations in the plasticity of functional traits indicate the differential impacts of abiotic and biotic factors on the structure and growth of trees in tropical dry forest fragments

Abiotic and biotic factors have considerable impact on the plasticity of plant functional traits, which influences forest structure and productivity; however, their inter-relationships have not been quantified for fragmented tropical dry forest (TDF) ecosystems. We asked the following questions: (1) what are the variations in the plasticity of functional traits due to soil moisture availability in TDF fragments? (2) what are the roles of soil nutrients and forest disturbances in influencing variations in the plasticity of functional traits in the TDF fragments? and (3) how do the variations in the plasticity of functional traits influence the structure and productivity of TDF fragments? Based on linear mixed-effects results, we observed significant variations among tree species for soil moisture content (SMC) under the canopy and selected functional traits across forest fragments. We categorized tree species across fragments by principal component analysis (PCA) and hierarchical clustering on principal components (HCPC) analyses into three functional types, viz., low wood density high deciduous (LWHD), high wood density medium deciduous (HWMD), and high wood density low deciduous (HWLD). Assemblage of functional traits suggested that the LWHD functional type exhibits a drought-avoiding strategy, whereas HWMD and HWLD adopt a drought-tolerant strategy. Our study showed that the variations in functional trait plasticity and the structural attributes of trees in the three functional types exhibit contrasting affinity with SMC, soil nutrients, and disturbances, although the LWHD functional type was comparatively more influenced by soil resources and disturbances compared to HWMD and HWLD along the declining SMC and edge distance gradients. Plasticity in functional traits for the LWHD functional type exhibited greater variations in traits associated with the conservation of water and resources, whereas for HWMD and HWLD, the traits exhibiting greater plasticity were linked with higher productivity and water transport. The cumulative influence of SMC, disturbances, and functional trait variations was also visible in the relative abundance of functional types in large and small sized fragments. Our analysis further revealed the critical differences in the responses of functional trait plasticity of the coexisting tree species in TDF, which suggests that important deciduous endemic species with drought-avoiding strategies might be prone to strategic exclusion under expected rises in anthropogenic disturbances, habitat fragmentation, and resource limitations.

The deterrent effects of individual monoterpene odours on the dietary decisions of African elephants

African savanna elephants use pre-ingestive olfactory cues when making dietary choices, and previous research has observed that elephant diet choice is negatively correlated with vegetation species that contain high concentrations of monoterpenes. However, the frequency and concentration of monoterpenes can vary dramatically across plant species. Thus, we aimed to explore the effects that the odours of individual monoterpenes have on elephant diet choice and how these effects vary with concentration. To do this, we conducted three odour-based choice experiments focusing on eight common monoterpenes found in the woody plants in Southern African savannas. In the first experiment, we tested whether elephant diet choice for a frequently consumed plant (Euclea crispa) was influenced by the addition of the odour of an individual monoterpene at a set concentration. In the second experiment, we explored the relative deterrence of each monoterpene. Lastly, we tested how elephant diet choice varied as a function of the addition of individual monoterpene odours at 5%, 10%, and 20% concentrations. We found that the elephants avoided most individual monoterpenes at high concentrations, with the exception being α-pinene. Furthermore, we found that the odours of some individual monoterpenes were, in fact, more deterrent than others. In the third experiment, we found that the elephants avoided β-pinene, limonene, ocimene, γ-terpinene, and terpinolene across all concentrations, but only avoided sabinene and linalool at high concentrations. Ultimately, our results show that the odour of individual monoterpenes may deter elephant consumption, but that this deterrent effect depends on both the monoterpene and its concentration.

Competition induces negative conspecific allelopathic effects on seedling recruitment

BACKGROUND AND AIMS

Some plant species suppress competitors through release of chemical compounds into the environment. As the production of allelochemicals may be costly, it would be beneficial if their production would only be induced when plants experience competition. We tested whether two plant species that frequently co-occur show evidence for induced allelopathy in response to intra- and interspecific competition.

METHODS

We used the annual forb Crepidiastrum sonchifolium and the perennial forb Achyranthes bidentata, which are native to China and predominantly occur in ruderal communities, as focal species. We first grew the species without competition, with intraspecific competition and in competition with each other. We chemically analysed aqueous extracts made from these plants to test for evidence that the competition treatments affected the metabolomic profiles of the species. We then tested the effects of the aqueous extracts on seed germination and seedling growth of both plant species.

KEY RESULTS

Metabolomic analysis revealed that competition treatments modified the chemical profiles of the two study species. The root lengths of A. bidentata and C. sonchifolium seedlings were reduced by the aqueous plant extracts. For seedling root length of A. bidentata, heterospecific allelopathy was more negative than conspecific allelopathy, but for germination of C. sonchifolium seeds, the reverse was true. Moreover, conspecific allelopathic effects on germination of A. bidentata seeds and on seedling root length of both species were most negative when the aqueous extracts were made from plants that had experienced competition. In the case of seedling root length of A. bidentata, this effect was most negative when the plants had experienced interspecific instead of intraspecific competition.

CONCLUSIONS

We showed that plants change their metabolomic profiles in response to competition, and that this correlated with allelopathic inhibition of conspecific seed germination and seedling growth. We suggest that autoallelopathy for seed germination could function as a mechanism to avoid strong competition by keeping the seeds in a dormant state.

Volatile Chemical Variation of Essential Oils and Their Correlation with Insects, Phenology, Ontogeny and Microclimate: Piper mollicomum Kunth, a Case of Study

The aim of this study was to monitor the volatile chemical composition from leaves and reproductive organs of Piper mollicomum Kunth (PM), in its reproduction period, as well as register inflorescence visitors, microclimate and phenological information. The essential oils (EOs) obtained from the different fresh organs by hydrodistillation were identified and quantified by Gas Chromatography/Mass Spectrometry (GC/MS) and by GC coupled to a Flame Ionization Detector (GC/FID), respectively. The cercentage content of some volatiles present in reproductive organs, such as limonene, 1,8-cineole, linalool and eupatoriochromene, increased during the maturation period of the inflorescences, and decreased during the fruiting period, suggesting a defense/attraction activities. Furtermore, a biosynthetic dichotomy between 1,8-cineole (leaves) and linalool (reproductive organs) was recorded. A high frequency of bee visits was registered weekly, and some correlations showed a positive relationship between this variable and terpenes. Microclimate has an impact on this species' phenological cycles and insect visiting behavior. All correlations between volatiles, insects, phenology and microclimate allowed us to present important data about the complex information network in PM. These results are extremely relevant for the understanding of the mechanisms of chemical-ecological plant-insect interactions in Piperaceae, a basal angiosperm.

Variations in mitragynine content in the naturally growing Kratom (Mitragyna speciosa) population of Thailand

We analyzed the content of mitragynine (MG) found in kratom leaves (Mitragyna speciosa) and the influence of different environmental conditions (air and soil variables) on the yield in various regions of Thailand. The content of MG in kratom leaves ranged from 7.5 - 26.6 mg g^-1 of dry leaf weight. Canonical correspondence analysis showed that the most significant environmental variables affecting the MG content among the various regions were light intensity, relative humidity, soil volumetric water content (VW), soil pH, and calcium. This study is a first step towards providing information about environmental conditions suitable to maximize the quality and quantity of bioactive alkaloids in kratom. Future studies should focus on leaf collection and the post-harvest processes in order to assure the desired alkaloidal content in finished products, when produced under suitable environmental conditions identified in this study.

Deciphering the growth stage specific bioactive diversity patterns in Murraya koenigii (L.) Spreng. using multivariate data analysis

The study was undertaken to characterize the total phenolics, flavonoids, essential oils, quinones, tannins and antioxidant activity of 15 samples of wild Murraya koenigii (L.) Spreng. (MK) leaves obtained from different locations of Himachal Pradesh at various growth stages. The results indicated a significant variation in total phenolic content which ranged from [(170.09 ± 4.59 to 303.57 ± 7.94) in pre-flowering, (266.48 ± 7.49 to 450.01 ± 11.78) in the flowering stage, and (212.72 ± 5.37 to 363.85 ± 9.79) in fruiting stage], expressed as mg tannic acid equivalents (TAE)/g. The total flavonoid content ranged from [(15.17 ± 0.36 to 33.40 ± 0.81) in pre-flowering, (25.16 ± 0.67 to 58.17 ± 1.52) in flowering stage, and (17.54 ± 0.42 to 37.34 ± 0.97) in fruiting stage], expressed as mg catechin equivalent (CE)/g. Total tannin content ranged from [(75.75 ± 1.69 to 143 ± 3.74) in pre-flowering, (116 ± 3.26 to 207 ± 5.42) in the flowering stage, and (47 ± 1.18 to 156 ± 4.05) in fruiting stage], expressed as mg TAE/g. The essential oil content ranged from (0.64 ± 0.01 to 0.89 ± 0.02%) in pre-flowering, (0.85 ± 0.02 to 1 ± 0.02%) in flowering stage, and (0.54 ± 0.01 to 0.7 ± 0.01%) in fruiting stage. Quinones ranged from [(2.05 ± 0.05 to 2.97 ± 0.07) in pre-flowering, (3.07 ± 0.07 to 4.95 ± 0.13) in flowering stage, and (1.02 ± 0.02 to 1.96 ± 0.04) in fruiting stage], expressed as mM/min/g tissue. Antioxidant activity ranged from [(4.01 ± 0.09 to 7.42 ± 0.17) in pre-flowering, (8.08 ± 0.19 to 13.60 ± 0.35) in flowering stage, and (3.11 ± 0.06 to 6.37 ± 0.15) in fruiting stage], expressed as μg/ml. Data was subjected to multivariate analysis using principal component analysis (PCA), hierarchical clustering analysis (HCA). This was used for elucidating the intricate relationships between the phytochemical properties. All evaluated phytochemical parameters significantly increased during the growth transition from pre-flowering to the flowering stage, followed by their gradual decrease during the fruiting stage. The present study can serve as rationale for commercializing MK for aromatic and phytopharmaceutical industries.

Scutellaria petiolata Hemsl. ex Lace & Prain (Lamiaceae).: A New Insight in Biomedical Therapies

The recent investigation was designed to explore Scutellaria petiolata Hemsl. ex Lace & Prain (Lamiaceae) whole plant in various extracts (methanol (SPM), dichloromethane (SPDCM), n-Hexane (SPNH), and aqueous (SPAQ) for a phytochemicals assessment, ESI-LC-MS chemical analysis, in vitro antimicrobials, and antioxidants and in vivo anti-inflammatory and analgesic potential. The qualitative detection shows that all the representative groups were present in the analyzed samples. The examined samples display the greatest amount of total flavonoid content (TFC, 78.2 ± 0.22 mg QE/mg) and total phenolic contents (TPC, 66.2 ± 0.33 mg GAE/g) in the SPM extract. The SPM extract proceeded to the ESI-LC-MS to identify the chemical constituents that presented nineteen bioactive ingredients, depicted for the first time from S. petiolata mainly contributed by flavonoids. The analyzed samples produced considerable capability to defy the microbes. The SPM extract was observed effective and offered an appreciable zone of inhibition (ZOI), 17.8 ± 0.04 mm against the bacterial strain Salmonellatyphi and 18.8 ± 0.04 mm against Klebsiella pneumonia. Moreover, the SPM extract also exhibited 19.4 ± 0.01 mm against the bacterial strains Bacillus atrophaeus and 18.8 ± 0.04 mm against Bacillus subtilis in comparison to the standard levofloxacin (Gram-negative) and erythromycin (Gram-positive) bacterial strains that displayed 23.6 ± 0.02 mm and 23.2 ± 0.05 mm ZOI, correspondingly. In addition to that, the SPD fraction was noticed efficiently against the fungal strains used with ZOI 19.07 ± 0.02 mm against Aspergillus parasiticus and 18.87 ± 0.04 mm against the Aspergillus niger as equated to the standard with 21.5 ± 0.02 mm ZOI. In the DPPH (2,2-diphenyl-1-picrylhydrazyl) analysis, the SPM extract had the maximum scavenging capacity with IC₅₀ of 78.75 ± 0.19 µg/mL succeeded by the SPDCM fraction with an IC₅₀ of 140.50 ± 0.20 µg/mL free radicals scavenging potential. Through the ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) assay, the similar extract (SPM) presented an IC₅₀ = 85.91 ± 0.24 µg/mL followed by the SPDCM fractions with IC₅₀ = 182.50 ± 0.35 µg/mL, and n-Hexane fractions were reported to be the least active between the tested samples in comparison to ascorbic acid of IC₅₀ = 67.14 ± 0.25 µg/mL for DPPH and IC₅₀ of 69.96 ± 0.18 µg/mL for ABTS assay. In the in vivo activities, the SPM extract was the most effective with 55.14% inhibition as compared to diclofenac sodium with 70.58% inhibition against animals. The same SPM crude extract with 50.88% inhibition had the most analgesic efficacy as compared to aspirin having 62.19% inhibition. Hence, it was assumed from our results that all the tested samples, especially the SPM and SPDCM extracts, have significant capabilities for the investigated activities that could be due to the presence of the bioactive compounds. Further research is needed to isolate the responsible chemical constituents to produce innovative medications.

Intra-specific kin recognition contributes to inter-specific allelopathy: A case study of allelopathic rice interference with paddy weeds

Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating inter-specific and intra-specific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin versus non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behaviour, allelochemical production and resource partitioning in the dominant weed competitor, as well as soil microbial communities. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced changes in root placement, altered weed carbon and nitrogen partitioning, but was associated with similar soil microbial communities. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighbouring collaborators (kin) or competitors and adjust their growth, competitiveness and chemical defense accordingly.

Vaccinium vitis-idaea L. Fruits: Chromatographic Analysis of Seasonal and Geographical Variation in Bioactive Compounds

Vaccinium vitis-idaea L. (lingonberry) fruits are promising sources of bioactive components with high potential in biomedical applications. Selection in plant breeding, determination of perspective wild clones with optimal growing conditions, and appropriate harvesting time leading to standardized extracts are key factors for achieving phytochemical quality to meet consumer’s needs. In the present study, lingonberry fruits collected along different phenological stages and from different geographical locations were analyzed for the composition of 56 constituents using validated chromatographic techniques. Early stages of lingonberries vegetation were determined as the best stages for obtaining high levels of most phenolics and triterpenoids, while the end of berry vegetation could be chosen as the optimal harvesting time in terms of anthocyanins. Furthermore, intensified continuous biosynthesis of triterpenoids and phenolic acids precursors after vegetation season in the winter sample was observed. Chemodiversity of lingonberries was affected by geographical factors as well as climatic and edaphic conditions, indicating different favorable growing conditions for the accumulation of particular compounds. Present findings could serve for breeders to obtain the highest yields of desirable lingonberry constituents, relevant in food and pharmaceutical industries.

Elucidating the relevance of high temperature and elevated CO2 in plant secondary metabolites (PSMs) production

Plant secondary metabolites (PSMs) are plant products that are discontinuously distributed throughout the plant kingdom. These secondary compounds have various chemical groups and are named according to their chemical constituents. For their ability to defend biotic and abiotic stresses they are considered as plants' defensive compounds. These metabolites take part in plant protection from insects, herbivores, and extreme environmental conditions. They are indirectly involved in plants’ growth and development. Secondary metabolites are also used by people in the form of medicines, pharmaceuticals, agrochemicals, colors, fragrances, flavorings, food additives, biopesticides, and drugs development. However, the increase in atmospheric temperature by several anthropogenic activities majorly by the combustion of hydrocarbons is a great issue now. On the other hand, climate change leaves an impact on the quality and quantity of plant secondary metabolites. It is measured that several greenhouse gases (GHGs) are present in the atmosphere, like Chlorofluorocarbons (CFCs), nitrous oxides (NO_x), Carbon dioxide (CO₂), Methane (CH₄) and Ozone (O₃), etc. CO₂, the major greenhouse gas is essential for photosynthesis. On the other hand, CO₂ plays a significant role in the up-regulation of atmospheric temperature. Plants produce various types of primary metabolites such as carbohydrates, proteins, fats, membrane lipids, nucleic acids, and chlorophyll as well as a variety of secondary metabolites from photosynthesis. The high temperature in the atmosphere creates heat stress for plants. As a matter of fact many morphological, physiological and biochemical changes occur in the plant. The high temperature invariably elicits the production of several secondary metabolites within plants. Various strategies have been universally documented to improve the production of PSMs. With this objective, the focus of the current review is to further investigate and discuss futuristic scenarios the effect of elevated CO₂ and high temperature on PSMs production which may perhaps beneficial for pharmaceutical industries, biotechnology industries, and also in climate change researches.

Determination of the Effect of Co-cultivation on the Production and Root Exudation of Flavonoids in Four Legume Species Using LC-MS/MS Analysis

Flavonoids play a key role in the regulation of plant-plant and plant-microbe interactions, and factors determining their release have been investigated in most of the common forage legumes. However, little is known about the response of flavonoid production and release to co-cultivation with other crop species. This study investigated alterations in the concentration of flavonoids in plant tissues and root exudates in four legumes [alfalfa (Medicago sativa L.), black medic (Medicago polymorpha L.), crimson clover (Trifolium incarnatum L.), and subterranean clover (Trifolium subterraneum L.)] co-cultivated with durum wheat [Triticum turgidum subsp. durum (Desf.) Husn.]. For this purpose, we carried out two experiments in a greenhouse, one with glass beads as growth media for root exudate extraction and one with soil as growth media for flavonoid detection in shoot and root biomass, using LC-MS/MS analysis. This study revealed that interspecific competition with wheat negatively affected legume growth and led to a significant reduction in shoot and root biomass compared with the same legume species grown in monoculture. In contrast, the concentration of flavonoids significantly increased both in legume biomass and in root exudates. Changes in flavonoid concentration involved daidzein, genistein, medicarpin, and formononetin, which have been found to be involved in legume nodulation and regulation of plant-plant interaction. We hypothesize that legumes responded to the co-cultivation with wheat by promoting nodulation and increasing exudation of allelopathic compounds, respectively, to compensate for the lack of nutrients caused by the presence of wheat in the cultivation system and to reduce the competitiveness of neighboring plants. Future studies should elucidate the bioactivity of flavonoid compounds in cereal-legume co-cultivation systems and their specific role in the nodulation process and inter-specific plant interactions such as potential effects on weeds.

The Ecological Importance of Allelopathy

Allelopathy (i.e., chemical interaction among species) was originally conceived as inclusive of positive and negative effects of plants on other plants, and we adopt this view. Most studies of allelopathy have been phenomenological, but we focus on studies that have explored the ecological significance of this interaction. The literature suggests that studies of allelopathy have been particularly important for three foci in ecology: species distribution, conditionality of interactions, and maintenance of species diversity. There is evidence that allelopathy influences local distributions of plant species around the world. Allelopathic conditionality appears to arise through coevolution, and this is a mechanism for plant invasions. Finally, allelopathy promotes species coexistence via intransitive competition, modifications of direct interactions, and (co)evolution. Recent advances additionally suggest that coexistence might be favored through biochemical recognition. The preponderance of phenomenological studies notwithstanding, allelopathy has broad ecological consequences.

Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 52 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Almond (Prunus dulcis cv. Casteltermini) Skin Confectionery By-Products: New Opportunity for the Development of a Functional Blackberry (Rubus ulmifolius Schott) Jam

This work proposes for the first time a model for reusing almond (Prunus dulcis cv. Casteltermini from Sicily, Southern Italy) skin to formulate a new functional blackberry (Rubus ulmifolius Schott) jam. For this purpose, blackberries were analysed fresh and as jam, traditionally prepared with a minimum fruit amount of 80%. Different percentages of almond skin (20, 15, and 10% w/w) were added to jam. The phytochemical profile of enriched jam was investigated by LC-ESI/LTQOrbitrap/MS analyses. Anthocyanins, hydrolysable tannins, and triterpenoids were identified in a blackberry extract, while proanthocyanidins, flavonoids, and oxylipins were identified in an almond extract. The n-hexane extract of P. dulcis skin, investigated by GC-MS, evidenced linoleic, palmitic, and oleic acids as the main abundant compounds. Samples were investigated for their antioxidant activity using DPPH, ABTS, β-carotene, and FRAP tests. The hypoglycaemic and hypolipidemic effects were studied by α-amylase, α-glucosidase, and lipase inhibitory assays. In order to evaluate the effect of thermal process on enriched jam bioactivity, pasteurisation was applied. An increase in activities for all samples was observed, in particular for jam enriched with 20% w/w of almond skin. Based on obtained data, and supported by sensory analysis, we propose enriched jam as a promising source of compounds useful for preventing diseases associated with oxidative stress.

Relaxation of putative plant defenses in a tropical agroecosystem

Evidence of the effects of agriculture on natural systems is widespread, but potential evolutionary responses in nontarget species are largely uncharacterized. To explore whether exposure to agrochemicals may influence selective pressures and phenotypic expression in nonagricultural plant populations, we characterized the expression of putative antiherbivore defense phenotypes in three nonagricultural species found upstream and downstream of irrigated rice fields in Guanacaste Province, Costa Rica. We found that plants downstream of chemically intensive agriculture showed shifts toward reduced expression of putative antiherbivore defenses relative to upstream counterparts. In two of three tested species, leaf extracts from downstream plants were more palatable to a generalist consumer, suggesting a possible reduction of chemical defenses. In one species with multiple modes of putative defenses, we observed parallel reductions of three metrics of putative biotic and physical defenses. These reductions were concurrent with reduced herbivore damage on downstream plants. Together, these results suggest that agriculture has the potential to alter intraspecific phenotypic expression, ecological interactions, and natural selection in nontarget plant populations.

Plant Genetics as a Tool for Manipulating Crop Microbiomes: Opportunities and Challenges

Growing human population size and the ongoing climate crisis create an urgent need for new tools for sustainable agriculture. Because microbiomes have profound effects on host health, interest in methods of manipulating agricultural microbiomes is growing rapidly. Currently, the most common method of microbiome manipulation is inoculation of beneficial organisms or engineered communities; however, these methods have been met with limited success due to the difficulty of establishment in complex farm environments. Here we propose genetic manipulation of the host plant as another avenue through which microbiomes could be manipulated. We discuss how domestication and modern breeding have shaped crop microbiomes, as well as the potential for improving plant-microbiome interactions through conventional breeding or genetic engineering. We summarize the current state of knowledge on host genetic control of plant microbiomes, as well as the key challenges that remain.

Plasticity in response to plant-plant interactions and water availability

The plastic responses of plants to abiotic and biotic environmental factors have generally been addressed separately; thus we have a poor understanding of how these factors interact. For example, little is known about the effects of plant-plant interactions on the plasticity of plants in response to water availability. Furthermore, few studies have compared the effects of intra- and interspecific interactions on plastic responses to abiotic factors. To explore the effects of intraspecific and interspecific plant-plant interactions on plant responses to water availability, we grew Leucanthemum vulgare and Potentilla recta with a conspecific or the other species, and grew pairs of each species as controls in pots with the roots, but not shoots, physically separated. We subjected these competitive arrangements to mesic and dry conditions, and then measured shoot mass, root mass, total mass and root : shoot ratio and calculated plasticity in these traits. The total biomass of both species was highly suppressed by both intra- and interspecific interactions in mesic soil conditions. However, in drier soil, intraspecific interactions for both species and the effect of P. recta on L. vulgare were facilitative. For plasticity in response to water supply, when adjusted for total biomass, drought increased shoot mass, and decreased root mass and root : shoot ratios for both species in intraspecific interactions. When grown alone, there were no plastic responses in any trait except total mass, for either species. Our results suggested that plants interacting with other plants often show improved tolerance for drought than those grown alone, perhaps because of neighbor-induced shifts in plasticity in biomass allocation. Facilitative effects might also be promoted by plasticity to drought in root : shoot ratios.

Phenotypic plasticity in chemical defence of butterflies allows usage of diverse host plants

Host plant specialization is a major force driving ecological niche partitioning and diversification in insect herbivores. The cyanogenic defences of Passiflora plants keep most herbivores at bay, but not the larvae of Heliconius butterflies, which can both sequester and biosynthesize cyanogenic compounds. Here, we demonstrate that both Heliconius cydno chioneus and H. melpomene rosina have remarkable plasticity in their chemical defences. When feeding on Passiflora species with cyanogenic compounds that they can readily sequester, both species downregulate the biosynthesis of these compounds. By contrast, when fed on Passiflora plants that do not contain cyanogenic glucosides that can be sequestered, both species increase biosynthesis. This biochemical plasticity comes at a fitness cost for the more specialist H. m. rosina, as adult size and weight for this species negatively correlate with biosynthesis levels, but not for the more generalist H. c. chioneus. By contrast, H. m rosina has increased performance when sequestration is possible on its specialized host plant. In summary, phenotypic plasticity in biochemical responses to different host plants offers these butterflies the ability to widen their range of potential hosts within the Passiflora genus, while maintaining their chemical defences.

Determination of bioactive compounds in the nonmedicinal parts of Scrophularia ningpoensis using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry and chemometric analysis

Although Scrophulariae Radix (root of Scrophularia ningpoensis) has received much attention, little is known about the nonmedicinal parts of S. ningpoensis. A comprehensive evaluation of the multibioactive constituents in the flowers, rhizomes, leaves, and stems of S. ningpoensis during different growth stages would be of value to fully understand the potential medicinal properties of all parts of the plant. Ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometry was performed for accurately determining nine compounds in S. ningpoensis. The results indicated the content of total analytes in S. ningpoensis was in the order of flowers (81.82 mg/g) > roots (31.95 mg/g) > rhizomes (26.68 mg/g) > leaves (16.86 mg/g) > stems (14.35 mg/g). The chemometric analysis showed that these plant parts were rich in iridoids and should not be discarded during the processing of medicinal materials. Dynamic accumulation analysis suggested that the early flowering stage was the optimum time for harvesting flowers and appropriate amounts of stems and leaves. Moreover, considering the accumulation of constituents and biomass of medicinal materials, the medicinal parts should be harvested around December with the rhizomes attached. This research provides a theoretical basis and scientific evidence for comprehensive development and utilization of S. ningpoensis resources.

The Mastic Tree (Pistacia lentiscus L.) Leaves as Source of BACs: Effect of Growing Location, Phenological Stage and Extraction Solvent on Phenolic Content

RESEARCH BACKGROUND

Mastic tree (Pistacia lentiscus L.) of the Anacardiaceae family is an evergreen shrub from Mediterranean countries where it is used in traditional medicine. Analysis of P. lentiscus leaf, stem, fruit and root extracts showed high concentrations of principal groups of secondary metabolites (flavonoids, phenolic acids and tannins), suggesting the plant possesses great biological potential. Therefore, the aim of this research is to evaluate the impact of environmental parameters and the extraction solvent type on the concentration of phenols in mastic tree leaf extracts grown at four different locations along the Adriatic coast (Barbariga, Lun, Hvar and Vela Luka) during three phenological stages (early flowering, early fruiting and late fruiting).

EXPERIMENTAL APPROACH

Since mastic tree plant has phenolic compounds with different structures and chemical properties, ethanolic and methanolic leaf extracts were analysed using high-performance liquid chromatography (HPLC) coupled with UV/Vis PDA detector. Phenolic compounds were identified by comparing the retention times and spectral data with those of standards at 280 and 340 nm.

RESULTS AND CONCLUSIONS

In all samples, phenolic acids and flavonol glycosides were quantified, while catechin was quantified only in methanolic extracts. The 5-O-galloylquinic acid was determined as a predominant phenolic compound in all samples followed by monogalloyl glucose, 3,5-di-O-galloylquinic acid, 3,4,5-tri-O-galloylquinic acid and gallic acid, respectively. Myricetin-3-O-rhamnoside was found to be the predominant flavonol glycoside followed by myricetin-3-O-glucoside, myricetin-3-O-glucuronide, quercetin-3-O-rhamnoside and derivative of flavonol glycoside. The mass concentration of these compounds significantly varied during different phenological stages, at different growing locations and used extraction solvents. The highest phenolic mass concentration was determined in the samples harvested at Hvar growing location and extracted in 80% methanol. The highest total phenolic acid mass concentration was obtained in the samples harvested during the flowering phenological stage and the highest total flavonoid mass concentration in the samples harvested during the early fruiting stage.

NOVELTY AND SCIENTIFIC CONTRIBUTION

The obtained data provide a better understanding of the P. lentiscus species phenolic concentration, which can lead to further investigations regarding the valorisation of mastic tree leaves as pharmaceutical products or as food products with added value.

Habitat variations affect morphological, reproductive and some metabolic traits of Mediterranean Centaurea glomerata Vahl populations

Centaurea glomerata Vahl is an annual, monoecious and herbaceous member of Asteraceae, found in some localities of different topographic features/habitat conditions along the Mediterranean coastal region of Egypt. This study aimed to investigate some environmental gradients including edaphic and climate criteria on morphological, reproductive traits as well as phenolic and flavonoid metabolites in this species. Three distinct populations were selected. Two of them were located in coastal sand dunes (found in Rosetta region in Egypt); one was located on flat sand dunes, whereas the other grown on sloping ones. Meanwhile, the third population was represented in the rocky hillside of Burg El Arab region. The population detected in the sloping sand dunes showed best morphological and reproductive features, whilst the opposite was true for that represented on the rocky hillside. Moreover, the free phenolic and flavonoid compounds prevailed in the later. The meteorological data revealed that the rocky hillside received relatively lower minimum temperature and higher solar irradiance, while the sand dunes of Rosetta showed more warmer conditions. Light intensity and wind speed were reduced on the sloping sand dunes. The Canonical Correspondence Analysis (CCA) exhibited a clear correlation between most of metabolites detected and the population found on the rocky hillside along with higher solar irradiance prevails. The morpho-reproductive traits were related to climatic gradients and some soil criteria. These results revealed that the changes in micro-topography, that may lead to change in soil and climate variables, is the most important environmental gradient that controls the morphological and biochemical features of C. glomerata. Solar irradiance and/or light intensity are key factors playing a role influencing the measured traits of this species. These findings suggest that accumulation of secondary metabolites could be a biochemical strategy and an adaptational criterion for such species under stress conditions.

The domestication syndrome in vegetatively propagated field crops

BACKGROUND

Vegetatively propagated crops are globally significant in terms of current agricultural production, as well as for understanding the long-term history of early agriculture and plant domestication. Today, significant field crops include sugarcane (Saccharum officinarum), potato (Solanum tuberosum), manioc (Manihot esculenta), bananas and plantains (Musa cvs), sweet potato (Ipomoea batatas), yams (Dioscorea spp.) and taro (Colocasia esculenta). In comparison with sexually reproduced crops, especially cereals and legumes, the domestication syndrome in vegetatively propagated field crops is poorly defined.

AIMS AND SCOPE

Here, a range of phenotypic traits potentially comprising a syndrome associated with early domestication of vegetatively propagated field crops is proposed, including: mode of reproduction, yield of edible portion, ease of harvesting, defensive adaptations, timing of production and plant architecture. The archaeobotanical visibility of these syndrome traits is considered with a view to the reconstruction of the geographical and historical pathways of domestication for vegetatively propagated field crops in the past.

CONCLUSIONS

Although convergent phenotypic traits are identified, none of them are ubiquitous and some are divergent. In contrast to cereals and legumes, several traits seem to represent varying degrees of plastic response to growth environment and practices of cultivation, as opposed to solely morphogenetic 'fixation'.

Effects of neighbour location and nutrient distributions on root foraging behaviour of the common sunflower

Plants regularly encounter patchily distributed soil nutrients. A common foraging response is to proliferate roots within high-quality patches. The influence of the social environment on this behaviour has been given limited attention, despite important fitness consequences of competition for soil resources among plants. Using the common sunflower (Helianthus annuus L.), we compared localized root proliferation in a high-quality patch by plants grown alone to that of plants in two different social environments: with a neighbouring plant sharing equal access to the high-quality patch, and with a neighbouring plant present but farther from the high-quality patch such that the focal individual was in closer proximity to the high-quality patch. Sunflowers grown alone proliferated more roots within high-nutrient patches than lower-nutrient soil. Plants decreased root proliferation within a high-nutrient patch when it was equidistant to a neighbour. Conversely, plants increased root proliferation when they were in closer proximity to the patch relative to a nearby neighbour. Such contingent responses may allow sunflowers to avoid competition in highly contested patches, but to also pre-empt soil resources from neighbours when they have better access to a high-quality patch. We also compared patch occupancy by sunflowers grown alone with two equidistant high-quality patches to occupancy by sunflowers grown with two high-quality patches and a neighbour. Plants grown with a neighbour decreased root length within shared patches but did not increase root length within high-quality patches they were in closer proximity to, perhaps because resource pre-emption may be less important for individuals when resources are more abundant. These results show that nutrient foraging responses in plants can be socially contingent, and that plants may account for the possibility of pre-empting limited resources in their foraging decisions.

Phenotypic plasticity of stomatal and photosynthetic features of four Picea species in two contrasting common gardens

Global climate change is expected to affect mountain ecosystems significantly. Phenotypic plasticity, the ability of any genotype to produce a variety of phenotypes under different environmental conditions, is critical in determining the ability of species to acclimate to current climatic changes. Here, to simulate the impact of climate change, we compared the physiology of species of the genus Picea from different provenances and climatic conditions and quantified their phenotypic plasticity index (PPI) in two contrasting common gardens (dry vs. wet), and then considered phenotypic plastic effects on their future adaptation. The mean PPI of the photosynthetic features studied was higher than that of the stomatal features. Species grown in the arid and humid common gardens were differentiated: the stomatal length (SL) and width (SW) on the adaxial surface, the transpiration rate (Tr) and leaf mass per area (LMA) were more highly correlated with rainfall than other traits. There were no significant relationships between the observed plasticity and the species' original habitat, except in P. crassifolia (from an arid habitat) and P. asperata (from a humid habitat). Picea crassifolia exhibited enhanced instantaneous efficiency of water use (PPI = 0.52) and the ratio of photosynthesis to respiration (PPI = 0.10) remained constant; this species was, therefore, considered to the one best able to acclimate when faced with the effects of climate change. The other three species exhibited reduced physiological activity when exposed to water limitation. These findings indicate how climate change affects the potential roles of plasticity in determining plant physiology, and provide a basis for future reforestation efforts in China.

Stress and defense responses in plant secondary metabolites production

In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

Allelochemicals and Signaling Chemicals in Plants

Plants abound with active ingredients. Among these natural constituents, allelochemicals and signaling chemicals that are released into the environments play important roles in regulating the interactions between plants and other organisms. Allelochemicals participate in the defense of plants against microbial attack, herbivore predation, and/or competition with other plants, most notably in allelopathy, which affects the establishment of competing plants. Allelochemicals could be leads for new pesticide discovery efforts. Signaling chemicals are involved in plant neighbor detection or pest identification, and they induce the production and release of plant defensive metabolites. Through the signaling chemicals, plants can either detect or identify competitors, herbivores, or pathogens, and respond by increasing defensive metabolites levels, providing an advantage for their own growth. The plant-organism interactions that are mediated by allelochemicals and signaling chemicals take place both aboveground and belowground. In the case of aboveground interactions, mediated air-borne chemicals are well established. Belowground interactions, particularly in the context of soil-borne chemicals driving signaling interactions, are largely unknown, due to the complexity of plant-soil interactions. The lack of effective and reliable methods of identification and clarification their mode of actions is one of the greatest challenges with soil-borne allelochemicals and signaling chemicals. Recent developments in methodological strategies aim at the quality, quantity, and spatiotemporal dynamics of soil-borne chemicals. This review outlines recent research regarding plant-derived allelochemicals and signaling chemicals, as well as their roles in agricultural pest management. The effort represents a mechanistically exhaustive view of plant-organism interactions that are mediated by allelochemicals and signaling chemicals and provides more realistic insights into potential implications and applications in sustainable agriculture.

…Fell Upas Sits, the Hydra-Tree of Death †, or the Phytotoxicity of Trees

The use of natural products that can serve as natural herbicides and insecticides is a promising direction because of their greater safety for humans and environment. Secondary metabolites of plants that are toxic to plants and insects-allelochemicals-can be used as such products. Woody plants can produce allelochemicals, but they are studied much less than herbaceous species. Meanwhile, there is a problem of interaction of woody species with neighboring plants in the process of introduction or invasion, co-cultivation with agricultural crops (agroforestry) or in plantation forestry (multiclonal or multispecies plantations). This review describes woody plants with the greatest allelopathic potential, allelochemicals derived from them, and the prospects for their use as biopesticides. In addition, the achievement of and the prospects for the use of biotechnology methods in relation to the allelopathy of woody plants are presented and discussed.

Stress Adaptive Plasticity: Aegilops tauschii and Triticum dicoccoides as Potential Donors of Drought Associated Morpho-Physiological Traits in Wheat

The inconsistent prevalence of abiotic stress in most of the agroecosystems can be addressed through deployment of plant material with stress adaptive plasticity. The present study explores water stress induced plasticity for early root-shoot development, proline induction and cell membrane injury in 57 accessions of Aegilops tauschii (DD-genome) and 26 accessions of Triticum dicoccoides (AABB-genome) along with durum and bread wheat cultivars. Thirty three Ae. tauschii accessions and 18 T. dicoccoides accessions showed an increase in root dry weight (ranging from 1.8 to 294.75%) under water stress. Shoot parameters- length and biomass, by and large were suppressed by water stress, but genotypes with stress adaptive plasticity leading to improvement of shoot traits (e.g., Ae tauschii accession 14191 and T. dicoccoides accession 7130) could be identified. Water stress induced active responses, rather than passive repartitioning of biomass was indicated by better shoot growth in seedlings of genotypes with enhanced root growth under stress. Membrane injury seemed to work as a trigger to activate water stress adaptive cellular machinery and was found positively correlated with several root-shoot based adaptive responses in seedlings. Stress induced proline accumulation in leaf tissue showed marked inter- and intra-specific genetic variation but hardly any association with stress adaptive plasticity. Genotypic variation for early stage plasticity traits viz., change in root dry weight, shoot length, shoot fresh weight, shoot dry weight and membrane injury positively correlated with grain weight based stress tolerance index (r = 0.267, r = 0.404, r = 0.299, r = 0.526, and r = 0.359, respectively). In another such trend, adaptive seedling plasticity correlated positively with resistance to early flowering under stress (r = 0.372 with membrane injury, r = 0.286 with change in root length, r = 0.352 with change in shoot length, r = 0.268 with change in shoot dry weight). Overall, Ae. tauschii accessions 9816, 14109, 14128, and T. dicoccoides accessions 5259 and 7130 were identified as potential donors of stress adaptive plasticity. The prospect of the study for molecular marker tagging, cloning of plasticity genes and creation of elite synthetic hexaploid donors is discussed.

Effect of temperature on morphology, ginsenosides biosynthesis, functional genes, and transcriptional factors expression in Panax ginseng adventitious roots

This study researched the effect of temperature on growth and ginsenosides accumulation in adventitious root cultures of Panax ginseng. Results showed that the ginseng adventitious roots growth and differentiation ability could be affected faced with different incubation temperatures (15, 20, 25, and 30°C for 35 days). Besides, the research also demonstrated that low-temperature stimulation could promote the accumulation of ginsenosides and the content of total ginsenosides increased by 2.53 times at 10°C-7d (10°C for 7 days and then transferred to 25°C for 28 days) compared with that at 25°C. Moreover, the transcriptional levels of functional genes and PgWRKYs were analyzed by this study and the correlation analysis showed that GPS, SS, CYP716A47, CYP716A53v2, UGT74AE2, UGT94Q2, PgWRKY1, PgWRKY3, and PgWRKY8 were significantly correlated with total ginsenosides content. Furthermore, HPLC-ESI-MSⁿ analyzed that Malonyl-Rb₁ only existed in 10°C-7d group. PRACTICAL APPLICATIONS: The survey showed that after a certain time of stimulating P. ginseng adventitious roots at low temperature, the accumulation of ginsenosides could be enhanced as their expression of related genes were regulated. It provides a theoretical foundation for the mass production of ginsenosides by controlling the temperature conditions of P. ginseng adventitious roots.

Who is my neighbor? Volatile cues in plant interactions

One of the most important challenges for individual plants is coexistence with their neighbors. To compensate for their sessile lifestyle, plants developed complex and sophisticated chemical systems of communication among each other. Site-specific biotic and abiotic factors constantly alter the physiological activity of plants, which causes them to release various secondary metabolites in their environments. Volatile organic compounds (VOCs) are the most common cues that reflect a plant's current physiological status. In this sense, the identity of its immediate neighbors may have the greatest impact for a plant, as they share the same available resources. Plants constantly monitor and respond to these cues with great sensitivity and discrimination, resulting in specific changes in their growth pattern and adjusting their physiology, morphology, and phenotype accordingly. Those typical competition responses in receivers may increase their fitness as they can be elicited even before the competition takes place. Plant-plant interactions are dynamic and complex as they can include many different and important surrounding cues. A major challenge for all individual plants is detecting and actively responding only to "true" cues that point to real upcoming threat. Such selective responses to highly specific cues embedded in volatile bouquets are of great ecological importance in understanding plant-plant interactions. We have reviewed recent research on the role of VOCs in complex plant-plant interactions in plant-cross kingdom and highlighted their influence on organisms at higher trophic levels.

Climate Change Effects on Secondary Compounds of Forest Trees in the Northern Hemisphere

Plant secondary compounds (PSCs), also called secondary metabolites, have high chemical and structural diversity and appear as non-volatile or volatile compounds. These compounds may have evolved to have specific physiological and ecological functions in the adaptation of plants to their growth environment. PSCs are produced by several metabolic pathways and many PSCs are specific for a few plant genera or families. In forest ecosystems, full-grown trees constitute the majority of plant biomass and are thus capable of producing significant amounts of PSCs. We summarize older literature and review recent progress in understanding the effects of abiotic and biotic factors on PSC production of forest trees and PSC behavior in forest ecosystems. The roles of different PSCs under stress and their important role in protecting plants against abiotic and biotic factors are also discussed. There was strong evidence that major climate change factors, CO2 and warming, have contradictory effects on the main PSC groups. CO2 increases phenolic compounds in foliage, but limits terpenoids in foliage and emissions. Warming decreases phenolic compounds in foliage but increases terpenoids in foliage and emissions. Other abiotic stresses have more variable effects. PSCs may help trees to adapt to a changing climate and to pressure from current and invasive pests and pathogens. Indirect adaptation comes via the effects of PSCs on soil chemistry and nutrient cycling, the formation of cloud condensation nuclei from tree volatiles and by CO2 sequestration into PSCs in the wood of living and dead forest trees.

Plant neighbor detection and allelochemical response are driven by root-secreted signaling chemicals

Plant neighbor detection and response strategies are important mediators of interactions among species. Despite increasing knowledge of neighbor detection and response involving plant volatiles, less is known about how soil-borne signaling chemicals may act belowground in plant-plant interactions. Here, we experimentally demonstrate neighbor detection and allelopathic responses between wheat and 100 other plant species via belowground signaling. Wheat can detect both conspecific and heterospecific neighbors and responds by increasing allelochemical production. Furthermore, we show that (-)-loliolide and jasmonic acid are present in root exudates from a diverse range of species and are able to trigger allelochemical production in wheat. These findings suggest that root-secreted (-)-loliolide and jasmonic acid are involved in plant neighbor detection and allelochemical response and may be widespread mediators of belowground plant-plant interactions.

A case of behavioural diversification in male floral function - the evolution of thigmonastic pollen presentation

Obvious movements of plant organs have fascinated scientists for a long time. They have been studied extensively, but few behavioural studies to date have dealt with them, and hardly anything is known about their evolution. Here, we present a large experimental dataset on the stamen movement patterns found in the Loasaceae subfam. Loasoideae (Cornales). An evolutionary transition from autonomous-only to a combination of autonomous and thigmonastic stamen movement with increased complexity was experimentally demonstrated. We compare the stamen movement patterns with extensive pollinator observations and discuss it in the context of male mating behavior. Thigmonastic pollen presentation via stamen movements appears to be a crucial component of floral adaptation to pollinator behaviour, evolving in concert with complex adjustments of flower signal, reward and morphology. We hypothesize that rapid adjustments of pollen presentation timing may play a significant role in the diversification of this plant group, representing a striking example for the evolutionary significance of plant behaviour.

A broadleaf species enhances an autotoxic conifers growth through belowground chemical interactions

Plants may affect the performance of neighboring plants either positively or negatively through interspecific and intraspecific interactions. Productivity of mixed-species systems is ultimately the net result of positive and negative interactions among the component species. Despite increasing knowledge of positive interactions occurring in mixed-species tree systems, relatively little is known about the mechanisms underlying such interactions. Based on data from 25-year-old experimental stands in situ and a series of controlled experiments, we test the hypothesis that a broadleaf, non-N fixing species, Michelia macclurei, facilitates the performance of an autotoxic conifer Chinese fir (Cunninghamia lanceolata) through belowground chemical interactions. Chinese fir roots released the allelochemical cyclic dipeptide (6-hydroxy-1,3-dimethyl-8-nonadecyl-[1,4]-diazocane- 2,5-diketone) into the soil environment, resulting in self-growth inhibition, and deterioration of soil microorganisms that improve P availability. However, when grown with M. macclurei the growth of Chinese fir was consistently enhanced. In particular, Chinese fir enhanced root growth and distribution in deep soil layers. When compared with monocultures of Chinese fir, the presence of M. macclurei reduced release and increased degradation of cyclic dipeptide in the soil, resulting in a shift from self-inhibition to chemical facilitation. This association also improved the soil microbial community by increasing arbuscular mycorrhizal fungi, and induced the production of Chinese fir roots. We conclude that interspecific interactions are less negative than intraspecific ones between non-N fixing broadleaf and autotoxic conifer species. The impacts are generated by reducing allelochemical levels, enhancing belowground mutualisms, improving soil properties, and changing root distributions as well as the net effects of all the processes within the soil. In particular, allelochemical context alters the consequences of the belowground ecological interactions with a novel mechanism: reduction of self-inhibition through reduced release and increased degradation of an autotoxic compound in the mixed-species plantations. Such a mechanism would be useful in reforestation programs undertaken to rehabilitate forest plantations that suffer from problems associated with autotoxicity.

Untargeted metabolic profiling reveals geography as the strongest predictor of metabolic phenotypes of a cosmopolitan weed

Plants produce a multitude of metabolites that contribute to their fitness and survival and play a role in local adaptation to environmental conditions. The effects of environmental variation are particularly well studied within the genus Plantago; however, previous studies have largely focused on targeting specific metabolites. Studies exploring metabolome-wide changes are lacking, and the effects of natural environmental variation and herbivory on the metabolomes of plants growing in situ remain unknown. An untargeted metabolomic approach using ultra-high-performance liquid chromatography-mass spectrometry, coupled with variation partitioning, general linear mixed modeling, and network analysis was used to detect differences in metabolic phenotypes of Plantago major in fifteen natural populations across Denmark. Geographic region, distance, habitat type, phenological stage, soil parameters, light levels, and leaf area were investigated for their relative contributions to explaining differences in foliar metabolomes. Herbivory effects were further investigated by comparing metabolomes from damaged and undamaged leaves from each plant. Geographic region explained the greatest number of significant metabolic differences. Soil pH had the second largest effect, followed by habitat and leaf area, while phenological stage had no effect. No evidence of the induction of metabolic features was found between leaves damaged by herbivores compared to undamaged leaves on the same plant. Differences in metabolic phenotypes explained by geographic factors are attributed to genotypic variation and/or unmeasured environmental factors that differ at the regional level in Denmark. A small number of specialized features in the metabolome may be involved in facilitating the success of a widespread species such as Plantago major into such wide range of environmental conditions, although overall resilience in the metabolome was found in response to environmental parameters tested. Untargeted metabolomic approaches have great potential to improve our understanding of how specialized plant metabolites respond to environmental change and assist in adaptation to local conditions.

Effects of soil pyrene contamination on growth and phenolics in Norway spruce (Picea abies) are modified by elevated temperature and CO2

With the constant accumulation of polycyclic aromatic hydrocarbons (PAHs) in soil and increasing temperature and CO₂ levels, plants will inevitably be exposed to combined stress. Studies on the effects of such combined stresses are needed to develop mitigation and adaptation measures. Here, we investigated the effects of soil pyrene contamination (50 mg kg^-1) on growth and phenolics of 1-year-old Norway spruce seedlings from five different origins in Finland at elevated temperature (+ 2 °C) and CO₂ (+ 360 ppm). Pyrene significantly decreased spruce height growth (0-48%), needle biomass (0-44%), stem biomass (0-43%), and total phenolic concentrations in needles (2-13%) and stems (1-19%) compared to control plants. Elevated temperature alone did not affect growth but led to lower concentrations of total phenolics in needles (5-29%) and stems (5-18%) in both soil treatments. By contrast, elevated CO₂ led to higher needle biomass (0-39%) in pyrene-spiked soils and higher concentrations of stem phenolics (0-18%) in pyrene-spiked and control soils compared to ambient treatments. The decrease in height growth and phenolic concentrations caused by pyrene was greater at elevated temperature, while elevated CO₂ only marginally modified the response. Seedlings from different origins showed different responses to the combined environmental stressors. The changes in growth and in the quantity and quality of phenolics in this study suggest that future climate changes will aggravate the negative influence of soil pyrene pollution on northern conifer forest ecosystems.

Response of Plant Secondary Metabolites to Environmental Factors

Plant secondary metabolites (SMs) are not only a useful array of natural products but also an important part of plant defense system against pathogenic attacks and environmental stresses. With remarkable biological activities, plant SMs are increasingly used as medicine ingredients and food additives for therapeutic, aromatic and culinary purposes. Various genetic, ontogenic, morphogenetic and environmental factors can influence the biosynthesis and accumulation of SMs. According to the literature reports, for example, SMs accumulation is strongly dependent on a variety of environmental factors such as light, temperature, soil water, soil fertility and salinity, and for most plants, a change in an individual factor may alter the content of SMs even if other factors remain constant. Here, we review with emphasis how each of single factors to affect the accumulation of plant secondary metabolites, and conduct a comparative analysis of relevant natural products in the stressed and unstressed plants. Expectantly, this documentary review will outline a general picture of environmental factors responsible for fluctuation in plant SMs, provide a practical way to obtain consistent quality and high quantity of bioactive compounds in vegetation, and present some suggestions for future research and development.

OH-initiated mechanistic pathways and kinetics of camphene and fate of product radical: a DFT approach

Present manuscript represents the DFT studies on the oxidation reaction of camphene initiated by OH radical and fate of product radicals using M06-2X functional along with 6-31+G(d,p) basis set. Intrinsic reaction calculation is done for transition states involving OH-addition reactions which proceed via reaction complexes proceeding to the formation of transition states. The rate constant calculated by using canonical transition state theory at 298 K and 1 atm is found to be 5.67 × 10^-11 cm³ molecule^-1 s^-1 which is in good agreement with the experimental rate constant. The atmospheric lifetime of the titled molecule has also been reported in our work.

Interference of allelopathic rice with penoxsulam-resistant barnyardgrass

BACKGROUND

Despite increasing knowledge of allelopathic rice interference with barnyardgrass, relatively little is known about its action on herbicide-resistant barnyardgrass. The incidence of herbicide-resistant barnyardgrass is escalating in paddy fields. Knowledge of the interference of allelopathic rice with herbicide-resistant barnyardgrass and the potential mechanisms involved is warranted.

RESULTS

Penoxsulam-resistant and -susceptible barnyardgrass biotypes were identified and segregated from a putative penoxsulam-resistant population occurring in paddy fields in China. Allelopathic rice inhibited the growth of barnyardgrass roots more than shoots, regardless of biotype. In particular, there was a stronger inhibition for resistant barnyardgrass than for susceptible barnyardgrass. Allelopathic rice significantly reduced total root length, total root area, maximum root amplitude and maximum root depth in barnyardgrass. Furthermore, the rice allelochemicals tricin and momilactone B inhibited the growth of both resistant and susceptible barnyardgrass. Compared with root contact, root segregation significantly increased inhibition of barnyardgrass with an increase in rice allelochemicals. Root exudates from barnyardgrass induced the production of rice allelochemicals, but the effect of susceptible barnyardgrass was much stronger than that of resistant barnyardgrass.

CONCLUSION

Allelopathic rice can interfere with the growth of penoxsulam-resistant barnyardgrass through allelochemical-mediated root interactions. This type of allelopathic interference may provide a non-herbicidal alternative for herbicide-resistant weed management in paddy systems. © 2017 Society of Chemical Industry.

Bacterial phytopathogen infection disrupts belowground plant indirect defense mediated by tritrophic cascade

Plants can defend themselves against herbivores through activation of defensive pathways and attraction of third-trophic-level predators and parasites. Trophic cascades that mediate interactions in the phytobiome are part of a larger dynamic including the pathogens of the plant itself, which are known to greatly influence plant defenses. As such, we investigated the impact of a phloem-limited bacterial pathogen, Candidatus Liberibacter asiaticus (CLas), in cultivated citrus rootstock on a well-studied belowground tritrophic interaction involving the attraction of an entomopathogenic nematode (EPN), Steinernema diaprepesi, to their root-feeding insect hosts, Diaprepes abbreviatus larvae. Using belowground olfactometers, we show how CLas infection interferes with this belowground interaction by similarly inducing the release of a C12 terpene, pregeijerene, and disconnecting the association of the terpene with insect presence. D. abbreviatus larvae that were not feeding but in the presence of a CLas-infected plant were more likely to be infected by EPN than those near uninfected plants. Furthermore, nonfeeding larvae associated with CLas-infected plants were just as likely to be infected by EPN as those near noninfected plants with D. abbreviatus larval damage. Larvae of two weevil species, D. abbreviatus and Pachnaeus litus, were also more attracted to plants with infection than to uninfected plants. D. abbreviatus larvae were most active when exposed to pregeijerene at a concentration of 0.1 μg/μl. We attribute this attraction to CLas-infected plants to the same signal previously thought to be a herbivore-induced plant volatile specifically induced by root-feeding insects, pregeijerene, by assessing volatiles collected from the roots of infected plants and uninfected plants with and without feeding D. abbreviatus. Synthesis. Phytopathogens can influence the structuring of soil communities extending to the third trophic level. Field populations of EPN may be less effective at host-finding using pregeijerene as a cue in citrus grove agroecosystems with high presence of CLas infection.

Interference of allelopathic rice with paddy weeds at the root level

Despite increasing knowledge of the involvement of allelopathy in negative interactions among plants, relatively little is known about its action at the root level. This study aims to enhance understanding of interactions of roots between a crop and associated weeds via allelopathy. Based on a series of experiments with window rhizoboxes and root segregation methods, we examined root placement patterns and root interactions between allelopathic rice and major paddy weeds Cyperus difformis, Echinochloa crus-galli, Eclipta prostrata, Leptochloa chinensis and Oryza sativa (weedy rice). Allelopathic rice inhibited growth of paddy weed roots more than shoots regardless of species. Furthermore, allelopathic rice significantly reduced total root length, total root area, maximum root width and maximum root depth of paddy weeds, while the weeds adjusted horizontal and vertical placement of their roots in response to the presence of allelopathic rice. With the exception of O. sativa (weedy rice), root growth of weeds avoided expanding towards allelopathic rice. Compared with root contact, root segregation significantly increased inhibition of E. crus-galli, E. prostrata and L. chinensis through an increase in rice allelochemicals. In particular, their root exudates induced production of rice allelochemicals. However, similar results were not observed in C. difformis and O. sativa (weedy rice) with either root segregation or root exudate application. The results demonstrate that allelopathic rice interferes with paddy weeds by altering root placement patterns and root interactions. This is the first case of a root behavioural strategy in crop-weed allelopathic interaction.

Age- and environment-dependent changes in chemical defences of larval and post-metamorphic toads

BACKGROUND

Chemical defences are widespread in animals, but how their production is adjusted to ecological conditions is poorly known. Optimal defence theory predicts that inducible defences are favoured over constitutive defences when toxin production is costly and the need for it varies across environments. However, if some environmental changes occur predictably (e.g. coupled to transitions during ontogeny), whereas others are unpredictable (e.g. predation, food availability), changes in defences may have constitutive as well as plastic elements. To investigate this phenomenon, we raised common toad (Bufo bufo) tadpoles with ad libitum or limited food and in the presence or absence of chemical cues on predation risk, and measured their toxin content on 5 occasions during early ontogeny.

RESULTS

The number of compounds showed limited variation with age in tadpoles and was unaffected by food limitation and predator cues. The total amount of bufadienolides first increased and later decreased during development, and it was elevated in young and mid-aged tadpoles with limited food availability compared to their ad libitum fed conspecifics, whereas it did not change in response to cues on predation risk. We provide the first evidence for the active synthesis of defensive toxin compounds this early during ontogeny in amphibians. Furthermore, the observation of increased quantities of bufadienolides in food-restricted tadpoles is the first experimental demonstration of resource-dependent induction of elevated de novo toxin production, suggesting a role for bufadienolides in allelopathy.

CONCLUSIONS

Our study shows that the evolution of phenotypic plasticity in chemical defences may depend on the ecological context (i.e. predation vs. competition). Our results furthermore suggest that the age-dependent changes in the diversity of toxin compounds in developing toads may be fixed (i.e., constitutive), timed for the developmental stages in which they are most reliant on their chemical arsenal, whereas inducible plasticity may prevail in the amount of synthesized compounds.