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Plants have to cope with a plethora of biotic stresses such as herbivory and pathogen attacks throughout their life cycle. The biotic stresses typically trigger rapid emissions of volatile products of lipoxygenase (LOX) pathway (LOX products: various C6 aldehydes, alcohols, and derivatives, also called green leaf volatiles) associated with oxidative burst. Further a variety of defense pathways is activated, leading to induction of synthesis and emission of a complex blend of volatiles, often including methyl salicylate, indole, mono-, homo-, and sesquiterpenes. The airborne volatiles are involved in systemic responses leading to elicitation of emissions from non-damaged plant parts. For several abiotic stresses, it has been demonstrated that volatile emissions are quantitatively related to the stress dose. The biotic impacts under natural conditions vary in severity from mild to severe, but it is unclear whether volatile emissions also scale with the severity of biotic stresses in a dose-dependent manner. Furthermore, biotic impacts are typically recurrent, but it is poorly understood how direct stress-triggered and systemic emission responses are silenced during periods intervening sequential stress events. Here we review the information on induced emissions elicited in response to biotic attacks, and argue that biotic stress severity vs. emission rate relationships should follow principally the same dose-response relationships as previously demonstrated for different abiotic stresses. Analysis of several case studies investigating the elicitation of emissions in response to chewing herbivores, aphids, rust fungi, powdery mildew, and Botrytis, suggests that induced emissions do respond to stress severity in dose-dependent manner. Bi-phasic emission kinetics of several induced volatiles have been demonstrated in these experiments, suggesting that next to immediate stress-triggered emissions, biotic stress elicited emissions typically have a secondary induction response, possibly reflecting a systemic response. The dose-response relationships can also vary in dependence on plant genotype, herbivore feeding behavior, and plant pre-stress physiological status. Overall, the evidence suggests that there are quantitative relationships between the biotic stress severity and induced volatile emissions. These relationships constitute an encouraging platform to develop quantitative plant stress response models.

Edge effect is a key process influencing populations and communities, particularly in fragmented landscapes. A general analytical framework has been proposed to quantify the strength of the edge effects (extent and magnitude); however, factors determining the later remain poorly explored. Using a continuous approach we explore the response of dung beetle species and assemblages to ecotones which differ in environmental dissimilarity in the Southern Atlantic forest of Argentina. Using baited pitfall traps and automatic sensors, we estimated dung beetle abundance, microclimatic conditions and vegetation structure along five different forest-plantations transects. At the assemblages level, the majority of species showed either edge avoidance or preference; however, the response depended on the environmental dissimilarity between habitats (plantation and native forest) and varied from a neutral response on mature plantations (low contrast ecotone) to edge avoidance on recent ones (high contrast ecotone). At the species level, the degree of habitat specialization explains the differential response of species to edge effects; more specialized species showed stronger edge response while generalist species showed softer or neutral responses. Environmental dissimilarity between confronted habitats and species specialization explain the quantitative component of edge effects on species and assemblages. Functional groups (rollers and tunnellers) often showed opposite responses to edge effects. At the landscape level, functional connectivity of forest fragments is probably drastically reduced by high contrasts matrices (such as recent plantations) for native forest species, whereas soft ecotones (such as native forest-mature plantations) maintained functional connectivity. These results are particularly relevant on highly fragmented landscapes, such as the Atlantic forest, where edge effect is probably one the most important mechanisms affecting native species and communities.

In many science and engineering systems both quantitative and qualitative output observations are collected. If modeled separately the important relationship between the two types of responses is ignored. In this article, we propose a Bayesian hierarchical modeling framework to jointly model a continuous and a binary response. Compared with the existing methods, the Bayesian method overcomes two restrictions. First, it solves the problem in which the model size (specifically, the number of parameters to be estimated) exceeds the number of observations for the continuous response. We use one example to show how such a problem can easily occur if the design of the experiment is not proper; all the frequentist approaches would fail in this case. Second, the Bayesian model can provide statistical inference on the estimated parameters and predictions, whereas it is not clear how to obtain inference using the latest method proposed by Deng and Jin ( 2015 ), which jointly models the two responses via constrained likelihood. We also develop a Gibbs sampling scheme to generate accurate estimation and prediction for the Bayesian hierarchical model. Both the simulation and the real case study are shown to illustrate the proposed method.

Abrupt temperature changes and warming hiatuses have a great impact on socioeconomic systems; however, their mechanisms remain unclear. In this study, the quantitative mechanisms of the responses of abrupt seasonal temperature changes and warming hiatuses in China to their influencing factors were analysed using the monthly mean temperature (Tav), mean minimum temperature (Tnav), and mean maximum temperature (Txav) from 622 meteorological stations in China covering 1951–2018, the CMIP6 model data, and data at large spatial scales, including Atlantic multidecadal oscillation (AMO) data. The results showed that the contributions of the influencing factors to the abrupt changes in Tav, Tnav, and Txav showed large spatial variability and peaked in the spring and summer and bottomed out in the autumn. The Pacific decadal oscillation (PDO) greatly impacted the abrupt temperature changes in Northeast China and North China at a contribution rate of approximately 12%, strongly influenced the abrupt temperature changes south of the Yangtze River, and markedly influenced the abrupt temperature changes in Northwest China. The AMO had a large impact on temperature in most regions of China in all seasons except for the summer. The MEI mainly affected the abrupt seasonal temperature changes in the region between 25° N and 35° N. The Arctic oscillation (AO) substantially impacted the warming hiatuses in Northeast China in the winter at a contribution rate of approximately 12%. These influencing factors contributed less to warming hiatuses than to abrupt temperature changes. Among the regional influencing factors, AP and WS greatly impacted warming hiatuses, more so than abrupt temperature changes, while relative humidity (RH) and solar radiation (SR) contributed little to warming hiatuses.

Key messageMassive infection of Populus × petrovskiana leaves by petiole gall aphids (Pemphigus spyrothecae) significantly decreased leaf dry mass per unit area, N content per dry mass and net assimilation rate per area, and increased stomatal conductance, leaf dry mass per fresh mass, and constitutive emissions of isoprene. The infection also induced emissions of green leaf volatiles, monoterpenes and benzenoids. The emissions scaled with the infection severity as assessed by dry gall mass per leaf dry mass.Poplar spiral gall aphid (Pemphigus spyrothecae) forms galls on the petiole in poplars (Populus) and mass infestations are frequent in poplar stands, but how these parasite gall infestations can affect the leaf lamina structure, photosynthetic rate and constitutive and stress volatile emissions is unknown. We investigated how the infestation by the petiole gall aphids affects lamina photosynthetic characteristics (net assimilation rate, stomatal conductance), C and N contents, and constitutive isoprene and induced volatile emissions in Populus × petrovskiana. The dry gall mass per leaf dry mass (Mg/Ml) was used as a quantitative measure of the severity of gall infestation. Very high fraction of leaf biomass was invested in gall formation with Mg/Ml varying between 0.5 and 2. Over the whole range of the infestation severities, net assimilation rate per area, leaf dry mass per unit area and N content decreased with increasing the severity of infestation. In contrast, stomatal conductance, leaf dry mass per fresh mass, constitutive isoprene emissions, and induced green leaf volatile (GLV), monoterpene, sesquiterpene and benzenoid emissions increased with increasing the severity of gall infestation. The rates of induced emissions were low and these emissions were associated with methyl jasmonate release from leaf laminas. The data demonstrate that petiole gall infestations lead to major changes in leaf lamina sink–source relationships and leaf water relations, thereby significantly altering lamina photosynthesis. Modifications in stress-induced emissions likely indicated systemic signaling triggered by jasmonate transported from the petiole galls to the lamina where jasmonate elicited a cascade of volatile emission responses. Enhanced isoprene emissions and induced volatile emissions can play a major role in indirect defense against other herbivores, securing the food source for the gall aphids. In conclusion, a massive infestation by petiole gall aphids can profoundly modify the foliage photosynthetic performance and volatile emission profiles in poplars.

Aim: To move towards modelling spatial abundance patterns and to evaluate the relative impacts of climatic change upon species abundances as opposed to range extents. Location: Southern Africa, including Lesotho, Namibia, South Africa, Swaziland and Zimbabwe. Methods: Quantitative response surface models were fitted for 78 bird species, mostly endemic (68) or near-endemic to the region, to model relationships between species reporting rates (i.e. the proportion of checklists reporting a species for a particular grid cell), as recorded by the Southern African Bird Atlas Project, and four bioclimatic variables derived from climatic data for the period 1961—90. With caution, reporting rates can be used as a proxy for abundance. Models were used to project potential impacts of a series of projected climatic change scenarios upon species abundance patterns and range extents. Results: Most models obtained were robust with good predictive power. Projections of potential future abundance patterns indicate that the magnitude of impacts upon a proxy for abundance are greater than those upon range extent for the majority of species (82% by 2071—2100). For most species (74%) both abundance and range extent are projected to decrease by 2100. Impacts are especially severe if species are unable to realize projected range changes; when only the area of a species' simulated present range is considered, overall abundance decreases of more than 80% are projected for 19 (24%) of species examined. Main conclusions: Our results indicate that projected climatic changes are likely to elicit greater relative changes in species abundances than range extents. For most species examined changes were decreases, suggesting the impacts upon biodiversity are likely generally to be negative. These results also suggest that previous estimates of the proportion of species at increased risk of extinction as a result of climatic change may, in some cases, be under-estimates.

The benchmark dose (BMD) concept is increasingly utilized to analyze quantitative dose–response relationships in genetic toxicology. This methodology requires the user (i.e. the toxicologist) to a priori define a small increase over controls that is “acceptable” to be induced by a genotoxic test substance. The increase is called benchmark response (BMR) or critical effect size (CES), depending on the software used. To render the metrics calculated from the data of animals treated with the test substance applicable for risk assessment, the BMR or CES must represent biologically relevant changes of parameters measured in in vivo genotoxicity assays such as the Micronucleus, Comet, Transgenic rodent or Pig-a assay. Current recommendations for CES in genotoxicology are arbitrary (10% increase over mean vehicle controls) or based on limited, usually 5–6, data points (i.e. the standard deviation of the concurrent vehicle control group). We have, therefore, analyzed historical vehicle control data of standard in vivo genotoxicity test systems with statistical methods. Based on this evaluation, we illustrate limitations of the currently recommended CES values and propose a pragmatic approach that may contribute to better defining endpoint-specific CES values for BMD software like PROAST.

Climate change will determine a sharp increase in carbon dioxide in the following years. To study the influence of elevated carbon dioxide on plants, we grew 13 different species and varieties from the Brassicaceae family at three carbon dioxide concentrations: 400, 800, and 1200 ppmv. The photosynthetic parameters (assimilation rate and stomatal conductance to water vapor) increase for all species. The emission of monoterpenes increases for plants grown at elevated carbon dioxide while the total polyphenols and flavonoids content decrease. The chlorophyll content is affected only for some species (such as Lipidium sativum), while the β-carotene concentrations in the leaves were not affected by carbon dioxide.

Persian walnut (Juglans regia L., Juglandaceae), one of the essential nut crops, is affected by different diseases, including mite attacks which result in gall and erineum formation. As the proportion of leaf area covered by mite galls or erineum is typically relatively low, the impact on tree photosynthetic productivity is often considered minor, and no pest control management is usually suggested. However, the effect of erineum-forming mites on walnut photosynthesis might be disproportionately larger than can be predicted from the leaf area impacted. In the present study, we studied how the foliage photosynthetic characteristics, pigment contents, and stress-induced volatile organic compounds scaled with the severity of infection varied from 0% (control trees) to 9.9%, by erineum-forming mite Aceria erinea in J. regia. Both leaf net assimilation rate (up to 75% reduction) and stomatal conductance (up to 82%) decreased disproportionately, increasing infection severity. Leaf total chlorophyll and β-carotene contents also decreased with infection severity, although the reduction was less than for photosynthetic characteristics (28% for chlorophyll and 25% for β-carotene). The infection induced significant emissions of green leaves volatiles ((Z)-3-hexenol, (E)-2-hexenal, (Z)-3-hexenyl acetate and 1-hexanol), monoterpenes and the homoterpene 3-(E)-4,8-dimethyl-1,3,7-nonatriene, and these emissions scaled positively with the percentage of leaf area infected. These results collectively indicate that erineum-forming mite infection of walnut leaves results in profound modifications in foliage physiological characteristics that can significantly impact tree photosynthetic productivity.

The relationship between water level and biodiversity of aquatic plants has been broadly identified but not so frequently quantified, especially with regard to historical periods. We reconstructed historical water levels with decadal resolution and assessed the response of individual aquatic plant species and plant diversity to water level. Our analyses were based on diatoms and plant pollen preserved in sediments of a shallow lake. We disentangled the effects of physical and chemical components on the composition of diatom assemblages in the process of reconstructing water level. The results showed that water levels indicated compositional changes in sedimentary diatom assemblages in different time periods. Diatom assemblages in the lower sediment layers present a larger compositional change than the upper ones. Moreover, water level was linked to the abundance of aquatic vascular plants, especially the submerged macrophytes based on grey analysis. Data on both sedimentary abiotic parameters and annual precipitation indicated that water level had large temporal variations in the earlier time periods of lake formation. However, water level experienced a sharp decrease and tended to be less variable after the construction of water dams. The optimal water levels related to plant diversity were determined at 6.95 m and at 8.24 m based on the richness and the evenness of seven species which were indicative of water level. The latter included six diatom species (Eunotia pectinalis, Pseudostautosira brevistriata, Cymbella cornuta, Cyclotella meneghiniana, Nitzschia palea and Gomphonema gracile) and one submerged plant (Myriophyllum). Extremely high or low water levels dampened the diversity of aquatic plants. Obtaining long-term lake water levels and analyzing their relation with biotic and abiotic components help us to understand impacts of anthropogenic disturbance on shallow lakes and thus contribute to the maintenance of aquatic plant diversity.