Neighboring Plants Research Articles

Seasonal variation of responses to herbivory and volatile communication in sagebrush (Artemisia tridentata) (Asteraceae).

Plants can respond to insect herbivory in various ways to avoid reductions in fitness. However, the effect of herbivory on plant performance can vary depending on the seasonal timing of herbivory. We investigated the effects of the seasonal timing of herbivory on the performance of sagebrush (Artemisia tridentata). Sagebrush is known to induce systemic resistance by receiving volatiles emitted from clipped leaves of the same or neighboring plants, which is called volatile communication. Resistance to leaf herbivory is known to be induced most effectively after volatile communication in spring. We experimentally clipped 25% of leaves of sagebrush in May when leaves were expanding, or in July when inflorescences were forming. We measured the growth and flower production of clipped plants and neighboring plants which were exposed to volatiles emitted from clipped plants. The treatment conducted in spring reduced the growth of clipped plants. This suggests that early season leaf herbivory is detrimental because it reduces the opportunities for resource acquisition after herbivory, resulting in strong induction of resistance in leaves. On the other hand, the late season treatment increased flower production in plants exposed to volatiles, which was caused mainly by the increase in the number of inflorescences. Because the late season treatment occurred when sagebrush produces inflorescences, sagebrush may respond to late herbivory by increasing compensation ability and/or resistance in inflorescences rather than in leaves. Our results suggest that sagebrush can change responses to herbivory and subsequent volatile communication seasonally and that the seasonal variation in responses may reduce the cost of induced resistance.

Arbuscular mycorrhizal fungi contribute to overyielding by enhancing crop biomass while suppressing weed biomass in intercropping systems

Intercropping often produces more biomass than the average of the corresponding monocultures, particularly in sustainable, low-input agriculture. Characterizing plant-plant interactions is fundamental for a better understanding of the ecological functioning of intercropping. However, there is little information on whether mycorrhizal networks exhibit different effects upon intra- and interspecific plant interactions in intercropping systems. Microcosms with one inner and three outer compartments were used. The inner compartment was separated from the outer compartments by a 30-μm nylon mesh or a solid barrier or remained open to allow full interactions between plants grown in the different compartments, creating three treatments, namely −Roots−CMNs (solid barrier), −Roots+CMNs (mesh), and +Roots+CMNs (no barrier). Either faba bean (Vicia faba) or maize (Zea mays) was grown as the donor plant in the inner compartment. Maize was combined with maize, wheat (Triticum aestivum) or the weed species foxtail (Setaria viridis) as the neighboring plant species. Faba bean was combined with faba bean, maize, or foxtail. The low-P soil was inoculated with the arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae or remained uninoculated. In the absence of AMF, plant growth was restricted by P deficiency and root interactions did not significantly affect plant-plant interactions. The presence of AMF enhanced plant biomass (maize by 104.5 %, faba bean by 61.6 %) and nutrient (N and P) uptake. Significant overyielding occurred in treatments where roots and hyphal networks of all plant species intermingled. The weed (foxtail) was suppressed by interspecific interactions while maize and faba bean benefitted from a mycorrhizal network and the presence of intermingling roots. In low-P soils, mycorrhizal networks contribute to overyielding in intercropping by enhancing the biomass and nutrient uptake of the mycorrhiza-dependent plant species. The biomass depression of weed species by AMF and/or root interactions may have ecological implications in weed control in intercropping systems.

Neighborhood structure influences the convergence in light capture efficiency and carbon gain: an architectural approach for cloud forest shrubs.

Although plant competition is recognized as a fundamental factor that limits survival and species coexistence, its relative importance on light capture efficiency and carbon gain is not well understood. Here, we propose a new framework to explain the effects of neighborhood structures and light availability on plant attributes and their effect on plant performance in two understory shade-tolerant species (Palicourea padifolia (Roem. & Schult.) C.M. Taylor & Lorence and Psychotria elata (Swartz)) within two successional stages of a cloud forest in Costa Rica. Features of plant neighborhood physical structure and light availability, estimated by hemispherical photographs, were used to characterize the plant competition. Plant architecture, leaf attributes and gas exchange parameters extracted from the light-response curve were used as functional plant attributes, while an index of light capture efficiency (silhouette to total area ratio, averaged over all viewing angles, STAR) and carbon gain were used as indicators of plant performance. This framework is based in a partial least square Path model, which suggests that changes in plant performance in both species were affected in two ways: (i) increasing size and decreasing distance of neighbors cause changes in plant architecture (higher crown density and greater leaf dispersion), which contribute to lower STAR and subsequently lower carbon gain; and (ii) reductions in light availability caused by the neighbors also decrease plant carbon gain. The effect of neighbors on STAR and carbon gain were similar for the two forests sites, which were at different stages of succession, suggesting that the architectural changes of the two understory species reflect functional convergence in response to plant competition. Because STAR and carbon gain are variables that depend on multiple plant attributes and environmental characteristics, we suggest that changes in these features can be used as a whole-plant response approach to detect environmental filtering in highly diverse tropical forest communities.

Plant Clonal Integration Mediates the Horizontal Redistribution of Soil Resources, Benefiting Neighboring Plants.

Resources such as water taken up by plants can be released into soils through hydraulic redistribution and can also be translocated by clonal integration within a plant clonal network. We hypothesized that the resources from one (donor) microsite could be translocated within a clonal network, released into different (recipient) microsites and subsequently used by neighbor plants in the recipient microsite. To test these hypotheses, we conducted two experiments in which connected and disconnected ramet pairs of Potentilla anserina were grown under both homogeneous and heterogeneous water regimes, with seedlings of Artemisia ordosica as neighbors. The isotopes [15N] and deuterium were used to trace the translocation of nitrogen and water, respectively, within the clonal network. The water and nitrogen taken up by P. anserina ramets in the donor microsite were translocated into the connected ramets in the recipient microsites. Most notably, portions of the translocated water and nitrogen were released into the recipient microsite and were used by the neighboring A. ordosica, which increased growth of the neighboring A. ordosica significantly. Therefore, our hypotheses were supported, and plant clonal integration mediated the horizontal hydraulic redistribution of resources, thus benefiting neighboring plants. Such a plant clonal integration-mediated resource redistribution in horizontal space may have substantial effects on the interspecific relations and composition of the community and consequently on ecosystem processes.

Biotic resistance to tropical ornamental invasion

Summary We examined invasive, casual (found occasionally outside cultivation) and non‐invasive (found only in cultivation) species to investigate the role of species traits and two forms of biotic resistance (plant neighbours and herbivores) in limiting invasion in Hawaiian lowlands. Seeds of 21 species of common woody ornamentals from three plant families (Acanthaceae, Apocynaceae, Bignoniaceae) that are non‐invasive, casual or invasive in Hawai'i were outplanted at two field sites. We measured germination of seeds and growth and survival of seedlings for 1 year in plots with and without neighbours from the naturally assembled community. The presence of neighbours reduced survival in some species, mostly non‐invasive or casual species, and completely excluded two non‐invasive species from community plots. Damage from the existing community of herbivores was correlated with lower survival in the Acanthaceae and Bignoniaceae, but not the Apocynaceae. Non‐invasive and casual species had lower survival and growth rates than invasive species and lower photosynthetic rates in the presence of neighbours than invasive species. Non‐invasives without neighbours also had lower specific leaf area than invasives and casuals. We found evidence for barriers to invasion in some non‐invasive and casual species, including low growth rate, low survival, or low survival in the presence of neighbours. By contrast, five of the six invasives flowered and three began setting fruit within the duration of the experiment, as did one of the casual species. Synthesis. Our research demonstrates biotic resistance, presumably as a result of competition. Neighbouring plants reduced survival and growth for most species. For non‐invasive species with low survival and growth even without competition from neighbouring plants, this resulted in complete exclusion from community plots or such low growth rates that exclusion over longer time frames was likely. We also provide evidence for traits‐based barriers to invasion in non‐invasive and casual species. However, no single barrier to invasion was shared across all non‐invasive and casual species.

A framework for partitioning plant rooting profiles from neighbours using multiple data types

Aim Vertical root distributions (‘profiles’) influence plant water use and productivity, and the differentiation of root profiles between neighbouring species can indicate the degree of plant interactions and niche partitioning. However, quantifying multiple species' root distributions in the field can be labour intensive and highly destructive to the soil and plants. We describe a method for partitioning multiple species roots using minimally destructive methods to determine if neighbour interactions alter the root profile of a common desert shrub, Larrea tridentata (creosote bush). Location Sonoran Desert, central Arizona, USA. Methods We obtained root and soil samples from soil cores collected around Larrea growing alone and next to three different neighbouring species. Bulk root mass was measured for each soil sample, and Larrea and neighbouring species root presence was determined with molecular identification methods. Water extracted from the soil and paired stem samples was analysed for its stable isotope composition (D and 18O). Species-specific (i.e. Larrea and neighbouring species) root biomass and fractional active root area were estimated through a hierarchical statistical modelling approach that combined all three data sets and accounted for detection errors. Results The combined data model successfully partitioned Larrea root biomass from neighbouring plants and provided biologically relevant estimates of rooting profiles with greater certainty than individual analyses of each data source. The data model results indicate that plant neighbours alter Larrea's root profile; Larrea growing under tree species had significantly higher root biomass in shallow soil layers than Larrea growing alone. Conclusions Our framework requires minimally destructive sampling methods, and accounts for sampling errors associated with different methods. We demonstrate the utility of our approach with a common desert shrub species, which illustrated that plant neighbours can alter the Larrea vertical root profile. Our approach is useful in problematic study systems fraught with sample collection issues or supporting species with inhibitory compounds that prohibit the use of more sophisticated molecular methods to identify the presence of other species' roots.

Evaluation of European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) larval movement and survival in structured and seed blend refuge plantings

Blending Bacillus thuringiensis (Bt) corn and non-Bt corn seeds in the same bag is a convenient and easier compliance solution to satisfy refuge regulations. However, there has been considerable debate and concern about larval movement of the target insects in a seed blend because of its potential effect on the development of resistance. Reported here are studies to determine the larval movement of European corn borers, Ostrinia nubilalis (Hübner), in a seed blend compared to a structured refuge and their effects on survival, feeding injury and larval fitness. Also evaluated is the relative performance of a purple-seeded corn hybrid as a surrogate host plant for tracking gene flow. Seed blend and structured refuge arrangements of Agrisure GT/CB/LL Bt corn expressing Cry1Ab and isoline plants were evaluated at two locations in 2013 and 2014 by manually infesting refuge plants with first and second generation corn borer larvae. The majority of leaf and stalk injury was recorded on the refuge plant, which amounted to 66–83% of the total tunnel length. In both refuge arrangements, plant injury and the number of larvae recovered significantly decreased on neighboring plants with increasing distance away from the refuge plant in the same row. The relative decline in injury was much more pronounced in the seed blend, with neighbor Bt plants experiencing very minor tunneling or no injury at all due to the high dose trait. Eighty-nine percent fewer live larvae were also found on neighbor Bt plants in the seed blend compared to those found in the structured refuge plots. Larvae that moved to Bt plants as well as older instars that were manually placed on Bt plants failed to complete development. Comparison of the number of tunnels and larvae recovered per refuge plant indicated that the seed blend may not produce as many susceptible individuals as those produced in a structured refuge arrangement. Although the purple-seeded hybrid showed lower levels of ear and stalk injury, it could serve as an appropriate surrogate refuge plant to track gene flow.

Intraspecific genetic variation and species coexistence in plant communities.

Many studies report that intraspecific genetic variation in plants can affect community composition and coexistence. However, less is known about which traits are responsible and the mechanisms by which variation in these traits affect the associated community. Focusing on plant-plant interactions, we review empirical studies exemplifying how intraspecific genetic variation in functional traits impacts plant coexistence. Intraspecific variation in chemical and architectural traits promotes species coexistence, by both increasing habitat heterogeneity and altering competitive hierarchies. Decomposing species interactions into interactions between genotypes shows that genotype × genotype interactions are often intransitive. The outcome of plant-plant interactions varies with local adaptation to the environment and with dominant neighbour genotypes, and some plants can recognize the genetic identity of neighbour plants if they have a common history of coexistence. Taken together, this reveals a very dynamic nature of coexistence. We outline how more traits mediating plant-plant interactions may be identified, and how future studies could use population genetic surveys of genotype distribution in nature and methods from trait-based ecology to better quantify the impact of intraspecific genetic variation on plant coexistence.

Common Mycelium Network of Mycorrhizas Alters Plant Biomass and Soil Properties between Trifoliate Orange Seedlings

Common mycelium networks (CMNs) of arbuscular mycorrhizas link neighbour plants and thus exhibit important roles in underground communication of substances between plants. In this study, a two-compartmented rootbox separated by 37-μm (mycelium, but not root, can pass through the size mesh) or 0.45-μm (both mycelium and root can’t pass through the size mesh) mesh was used, where one compartment was inoculated with Paraglomus occultum. We confirmed whether CMNs establish between trifoliate orange seedlings and have the roles in improving both plant growth and soil properties in receptor plant (the plant inoculated without mycorrhizal fungi but infected by mycorrhizal mycelium of another inoculated plant). A CMN was formed between trifoliate orange seedlings under separation of 37-μm but not 0.45-μm mesh, resulting in a moderate root colonization of receptor plant. The mycorrhizal inoculation significantly increased leaf, stem, and root fresh weight and rhizospheric three glomalin-related soil protein (GRSP) concentrations, soil organic carbon, and mean weight diameter in the donor plant (the inoculated plant with mycorrhizal fungi). The CMN under 37-µm mesh condition had significantly positive effects on the above growth and soil properties in the receptor plant. Under 0.45-µm mesh, the AMF inoculation in donor plant considerably inhibited biomass production of receptor plant, but increased easily-extractable GRSP, total GRSP, soil organic carbon, and mean weight diameter in receptor plant. It suggested that AMF inoculation and the subsequent CMN establishment would benefit improvement of plant growth and soil aggregation and fertility in donor and receptor plant.

COAL-FIRED POWER PLANT AIRBORNE PARTICLES IMPACT TOWARDS HUMAN HEALTH

The explosion of global warming and climate change occurs parallel to the raise rise of earth development. These phenomena happen due to the deterioration of atmospheric environment rooted from human activity. Ranges of air pollutants had been discovered. However, this research focuses on airborne particles in particular that comes from the emissions of coal. Recently, Malaysia electricity demand is raising and leads to the diversification of its sources towards the non-renewable energy. Manjung coal-fired power plant emission had been recognised as one of the potential anthropogenic sources of airborne particles. 8-hours airborne particles sampling had been done at Manjung Power Plant in March and July 2011 with 7-hole sampler at 2 L/min air flow and cyclone sampler at 2.2 L/min airflow. This research found that total inhalable dust exceeds 96.78 %; PM10 standard of 0.15mg/m3.This study also found that the percentage ratio of respirable towards total inhalable dust is 33.49%. This study also found that, as the temperature increases, the airborne particles concentration also increases. It is believed that the smaller offers particulate higher degree of illness. Thus, it is believed, the airborne particles dissemination from its sources is affected by the climate of an environment. Whichcan be deposited into deeper part of lung and provide adverse health impact towards the public or residence of surrounding coal-fired power plant neighbourhood area, generally and coal workers, specifically.

Estimation in the Field of Individual Perennial Ryegrass Plant Position and Dry Matter Production Using a Custom‐Made High‐Throughput Image Analysis Tool

ABSTRACTPerennial ryegrass (Lolium perenne L.) is widely used in grazing systems across the temperate world. Continued persistence of ryegrass pastures depends on our ability to further our understanding of the key traits or attributes responsible for improved plant performance. To this end, plant improvement is highly dependent on precise phenotyping capabilities. However, in‐field phenotyping is labor intensive, relies on experienced operators, and is often considered cost prohibitive. The aim of this study was to determine the accuracy of an image analysis tool developed to locate and estimate dry matter (DM) production of individual plants growing in the field. Fifty plants were used to develop the image analysis tool and another 1100 to determine its accuracy. Dry matter was measured by weighing oven‐dried harvested plant material and estimated both with the image analysis tool and by visual scoring. The image analysis tool was faster and estimates of plant area were more highly correlated with measured DM values, potentially capturing 25% more of the variation, than those from visual growth scores. The tool was able to effectively locate and distinguish between neighboring plants. The accuracy of the tool was greatest for production values below 15 g, and the tool would benefit from further development to improve accuracy above this threshold.

Ethylene: Traffic Controller on Hormonal Crossroads to Defense.

Ethylene (ET) is an important hormone in plant responses to microbial pathogens and herbivorous insects, and in the interaction of plants with beneficial microbes and insects. Early ET signaling events during these biotic interactions involve activities of mitogen-activated protein kinases and ETHYLENE RESPONSE FACTOR transcription factors. Rather than being the principal regulator, ET often modulates defense signaling pathways, including those regulated by jasmonic acid and salicylic acid. Hormonal signal integrations with ET steer the defense signaling network to activate specific defenses that can have direct effects on attackers, or systemically prime distant plant parts for enhanced defense against future attack. ET also regulates volatile signals that attract carnivorous enemies of herbivores or warn neighboring plants. Conversely, ET signaling can also be exploited by attackers to hijack the defense signaling network to suppress effective defenses. In this review, we summarize recent findings on the significant role of ET in the plants' battle against their enemies.

Priming maize resistance by its neighbors: activating 1,4-benzoxazine-3-ones synthesis and defense gene expression to alleviate leaf disease.

Plant disease can be effectively suppressed in intercropping systems. Our previous study demonstrated that neighboring maize plants can restrict the spread of soil-borne pathogens of pepper plants by secreting defense compounds into the soil. However, whether maize plant can receive benefits from its neighboring pepper plants in an intercropping system is little attention. We examined the effects of maize roots treated with elicitors from the pepper pathogen Phytophthora capsici and pepper root exudates on the synthesis of 1,4-benzoxazine-3-ones (BXs), the expression of defense-related genes in maize, and their ability to alleviate the severity of southern corn leaf blight (SCLB) caused by Bipolaris maydis. We found that SCLB was significantly reduced after the above treatments. The contents of 1,4-benzoxazine-3-ones (BXs: DIBOA, DIMBOA, and MBOA) and the expression levels of BX synthesis and defense genes in maize roots and shoots were up-regulated. DIMBOA and MBOA effectively inhibited the mycelium growth of Bipolaris maydis at physiological concentrations in maize shoots. Further studies suggested that the defense related pathways or genes in maize roots and shoots were activated by elicitors from the P. capsici or pepper root exudates. In conclusion, maize increased the levels of BXs and defense gene expression both in roots and shoots after being triggered by root exudates and pathogen from neighboring pepper plants, eventually enhancing its resistance.

Variable Family Size Based Spatial Moving Correlations Model

It is well known that the autocorrelations among responses play a significant role in time series setup mainly for the purpose of forecasting. Similarly, in a spatial setup, spatial variation and correlations among responses collected from a large sequence of spatial locations are important parameters for any practical inferences. For example, variation in plant crop damages and correlations among neighboring plant crop damages are important parameters to understand before one can take suitable measure to prevent such damages in the future. In this setup, a group of neighboring plants or locations constitute a family, and the pairwise responses within a family of locations are likely to be correlated. Furthermore, the responses from neighboring families will also be correlated but they become uncorrelated when the locations are far apart. In this paper, we deal with modeling of spatial correlations for continuous data collected from non-linear sequence of locations and propose a pairwise linear mixed models-based moving or band correlation structure that reflects the correlations for within and between families. The proposed correlation structure is then exploited to develop the likelihood inferences for both variance and correlation parameters of the model. The regression parameters are also estimated. The correlation model and the inferences are illustrated using a monte carlo study for a simpler case with responses collected from a linear sequence of locations. The correlation mis-specification effects are also discussed.

Optimizing Crops for Biocontrol of Pests and Disease.

Volatile compounds and extrafloral nectar are common defenses of wild plants; however, in crops they bear an as-yet underused potential for biological control of pests and diseases. Odor emission and nectar secretion are multigene traits in wild plants, and thus form difficult targets for breeding. Furthermore, domestication has changed the capacity of crops to express these traits. We propose that breeding crops for an enhanced capacity for tritrophic interactions and volatile-mediated direct resistance to herbivores and pathogens can contribute to environmentally-friendly and sustainable agriculture. Natural plant volatiles with antifungal or repellent properties can serve as direct resistance agents. In addition, volatiles mediating tritrophic interactions can be combined with nectar-based food rewards for carnivores to boost indirect plant defense.

Root-associated fungal community response to drought-associated changes in vegetation community

Recent droughts in southwestern USA have led to large-scale mortality of piñon (Pinus edulis) in piñon-juniper woodlands. Piñon mortality alters soil moisture, nutrient and carbon availability, which could affect the root-associated fungal (RAF) communities and therefore the fitness of the remaining plants. We collected fine root samples at a piñon-juniper woodland and a juniper savannah site in central New Mexico. Roots were collected from piñon and juniper (Juniperus monosperma) trees whose nearest neighbors were live piñon, live juniper or dead piñon. RAF communities were analyzed by 454 pyrosequencing of the universal fungal ITS region. The most common taxa were Hypocreales and Chaetothyriales. More than 10% of ITS sequences could not be assigned taxonomy at the phylum level. Two of the unclassified OTUs significantly differed between savanna and woodland, had few like sequences in GenBank and formed new fungal clades with other unclassified RAF from arid plants, highlighting how little study has been done on the RAF of arid ecosystems. Plant host or neighbor did not affect RAF community composition. However, there was a significant difference between RAF communities from woodland vs. savanna, indicating that abiotic factors such as temperature and aridity might be more important in structuring these RAF communities than biotic factors such as plant host or neighbor identity. Ectomycorrhizal fungi (EM) were present in juniper as well as piñon in the woodland site, in contrast with previous research, but did not occur in juniper savanna, suggesting a potential shared EM network with juniper. RAF richness was lower in hosts that were neighbors of the opposite host. This may indicate competitive exclusion between fungi from different hosts. Characterizing these communities and their responses to environment and plant neighborhood is a step toward understanding the effects of drought on a biome that spans 19 000 000 ha of southwestern USA.

The Role of Competition and Seed Production Environment on the Success of Two Perennial Grass Species in a Roadside Restoration

When large-scale restorations are undertaken using local genotypes, wild-collected sources often undergo a generation in an agronomic environment for seed propagation. Currently, there is little information on how a single generation of agronomic production can alter seed success in restoration. In this study, we compare plants grown from wild-collected and agronomically-grown seed sources, originally sampled from the same wild populations. We asked if emergence and growth differed between seed sources (agronomically-grown or wild-collected) when initial levels of competition were manipulated in the first growing season by simultaneously sowing annual forbs and cataloging plant neighbors to assess competition at later stages. Our two study species, western wheatgrass ( Pascopyrum smithii ) and green needlegrass ( Nassella viridula ) did not exhibit a competitive response to annuals in the first growing season, and by the middle of the second growing season there was no effect of source environment on plant performance. Greater green needlegrass emergence from the agronomic source in the first year did not translate into more abundance or plant biomass by the middle of the second growing season. Competition was rarely important in suppressing the growth of these two native perennial grass species, but facilitation from neighboring forbs increased productivity of both species in the second growing season. Any maternal effects or selection imposed by the agronomic increase environment does not appear to affect seedling establishment and growth. Sowing annual forbs as part of restoration mixes may promote perennial grass growth as well as provide services to pollinators.

Allelotoxic effects of aqueous extract of leaf of Parthenium hysterophorus l. On cytomorphological behavior of allium cepa l. And lens Esculenta moench

Parthenium hysterophorus a species of Asteraceae, has gained a worldwide cognigence as weed due to its invasiveness at many parts of the world. It is well known for its allelopathic effect to various neighboring plants. The allelopathic effect of Parthenium leaf extract has been noted to affect the ability of plant cell division, the chromosomal conformity as well as the growth of Allium cepa and Lens esculenta . The present study illustrated that with the increase of concentration of leaf extract the mitotic index decreases and the percentage of chromosomal abnormality increases correspondingly destabilizing the growth behavior of the studied plants.

Limiting processes for perennial plant reintroduction to restore dry grasslands

In restored grasslands of southern Europe, perennial plants remain highly underrepresented compared with the reference ecosystems. We tested various treatments to reintroduce common perennial plant species (Brachypodium retusum, Poaceae, and Thymus vulgaris, Lamiaceae), which are usually not or poorly reintroduced via soil and hay transfer. Treatments included microenvironmental manipulations (rock cover and plant interactions) and two grazing intensities. Target perennial species were transplanted in 2002 in the reference grassland ecosystem (intact grassland area used as a control) and in two abandoned fields. Survival was assessed in June 2003 and June 2004. Target species shoot and root biomass were measured in June 2004. Grazing greatly reduced the survival and biomass of both target species and its effects were reinforced by summer drought: plants that did not establish well enough during the autumn and spring did not survive summer. The restored rock cover had a mild positive effect, particularly on B. retusum. There were no negative or positive plant neighbor interactions in the steppe, while there was competition in both abandoned fields. Competition was particularly intense in the abandoned melon field, composed of a dense sward of annual grasses (Bromus sp.). In order to reintroduce perennial species to dry grasslands, the ideal combination of treatments is to exclude or reduce grazing during the first year to allow seedlings to establish and to recreate adequate microenvironmental conditions. Reducing competition from arable weeds may help but is not essential in such dry grasslands.

Utilizing associational resistance for biocontrol: impacted by temperature, supported by indirect defence.

BackgroundAssociational herbivore resistance is potentiated by neighbouring heterogenic plant species that impact a focal plant’s attraction to herbivores or the damage that they cause. One mechanism to confer associational resistance is believed to be exposure to neighbour-emitted volatiles, the receivers of which range from intra- and interspecific neighbour plants to higher-trophic-level insects. In previous studies the passive adsorption of neighbour-emitted semivolatiles has been reported, but little is known regarding the mechanisms and ecological consequences on the receiver plant and its associated biota. To utilize volatile-based associational resistance for agricultural applications, it is imperative to know its effectiveness under varying diurnal temperatures and whether herbivore natural enemies, providing biological control, are impacted. Mimicking varying diurnal temperatures in a laboratory set-up, we assessed how the tritrophic model system Brassica oleracea var. italica (broccoli)–Plutella xylostella (crucifer specialist herbivore)–Cotesia vestalis (endoparasitoid of P. xylostella) is influenced by exposure to the natural semivolatile emitter plant Rhododendron tomentosum Harmaja.ResultsRhododendron tomentosum-exposed B. oleracea was less susceptible to P. xylostella oviposition at both night-time (12°C) and day-time (22°C) temperatures and less favoured and damaged by P. xylostella larvae at 12°C. Exposure did not interfere with indirect defence, i.e. attraction of the natural enemy C. vestalis on host-damaged, R. tomentosum-exposed B. oleracea under 22°C, while there was a reduction in attraction (marginal preference towards host-damaged B. oleracea) under 12°C.ConclusionsThe ability of R. tomentosum exposure to render associational resistance against an agriculturally important Brassica herbivore P. xylostella without severely compromising the specialist parasitoid C. vestalis host location encourages further studies on the potential of using this naturally abundant plant for biocontrol. The generality of our finding on temperature as a potential regulating mechanism for the efficacy of semivolatile emitter-based associational resistance towards specialist pest larval damage should be further studied in natural and agricultural associations. Our study emphasizes the need to develop techniques to compare volatiles at the leaf versus air interface and associate their appearance and ecological role with times of activity and level of specialisation of herbivores and their natural enemies.