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SummaryForest ecosystems are increasingly challenged by extreme events, e.g. pest and pathogen outbreaks, causing severe ecological and economical losses. Understanding the genetic basis of adaptive traits in tree species is of key importance to preserve forest ecosystemsAdaptive phenotypes, including susceptibility to two fungal pathogens (Diplodia sapinea and Armillaria ostoyae) and an insect pest (Thaumetopoea pityocampa), height and needle phenology were assessed in a range-wide common garden of maritime pine (Pinus pinaster Aiton), a widespread conifer in the western Mediterranean Basin and parts of the Atlantic coast.Broad-sense heritability was significant for height (0.497), needle phenology (0.231-0.468) and pathogen symptoms (0.413 for D. sapinea and 0.066 for A. ostoyae) measured after inoculation under controlled conditions, but not for pine processionary moth incidence assessed in the common garden. Genetic correlations between traits revealed contrasting trends for pathogen susceptibility to D. sapinea and A. ostoyae. Maritime pine populations from areas with high summer temperatures and frequent droughts were less susceptible to D. sapinea but more susceptible to A. ostoyae. An association study using 4,227 genome-wide SNPs revealed several loci significantly associated to each trait.This study provides important insights to develop genetic conservation and breeding strategies integrating tree responses to pathogens.
<p>It is widely observed that silicon availability (Si) can enhance plant growth and increase the tolerance of plants to a range of biotic and abiotic stresses, although the specific mechanisms underlying these positive effects are not always understood. Silicon is acquired by plants both actively via transporters located in roots and/or passively as plants transport water during transpiration. The relative importance of each of these mechanisms depends strongly on the plant species and the level of stress experienced by the plant. Currently there is a lively debate in the literature regarding the relationship between plant Si accumulation and transpiration rates. Rates of transpiration can affect the amount of Si moving through a plant and in turn the concentration of available Si in soils can make the plant less vulnerable to the effects of drought stress. In order to better understand these relationships between plant water fluxes and Si accumulation in leaves, nine angiosperm tree species (from five families including both deciduous and evergreen species) were grown in a greenhouse and exposed to contrasting watering treatments. For each species, three trees were well watered throughout the growing season whilst three others were exposed to water stress. Whole plant transpiration fluxes were monitored continuously with balances, and pre-dawn leaf water potentials were measured regularly during the experiment. In addition the foliar Si concentrations of each plant were measured by ICP-AES after alkaline fusion both at the beginning and the middle of the growing season. In this presentation, we show our first results examining the relationship between leaf Si concentrations and plant water fluxes in contrasting species. We tested the hypothesis that drought stress significantly decreased the foliar Si concentration in all of the species measured and that foliar Si concentrations were correlated with the cumulative transpiration rates of plants and thus expected to increase significantly over the growing season.&#160;</p>
<p>During the process of photosynthesis, leaves capture CO<sub>2</sub> from the atmosphere and rapidly convert it into a diverse array of primary and secondary metabolites. Plants maintain a core set of metabolic pathways that ensure the basic building blocks of life that are available for each plant species to function. However, as plants evolved on land, they began to allocate this carbon (C) to innovative secondary metabolites and organs (cuticles, roots, wood) that protected them from abiotic stress (UV radiation, aridity, freezing) and biotic attack (fungal pathogens and insect/animal herbivory). As plants expanded over the land surface and occupied different niches, the amount of C fixed by plants varied and the types of secondary compounds synthesised by plants began to differ. Little is known about the metabolic profiles of the dominant European tree species and how variable the metabolomes of individual tree species are to changes in site conditions such as nutrient availability or soil moisture status. This study took advantage of recent advances in high-resolution mass spectrometry (HRMS) and bioinformatic tools to compare the leaf metabolomes of 14 commercially important tree species grown across three common gardens. Alongside the metabolic profiles, important chemical and morphological data were also collected from the trees during sampling, including targeted analysis of specific leaf metabolites such as proteins and phenolic compounds to obtain quantitative information on how their concentrations varied between tree species and site. Our analysis showed that the metabolomes of each tree species statistically differ from one another, and this dissimilarity was highly conserved at all three sites, even though tree growth and mortality rates varied between species and site. Our analysis also clearly highlighted distinct metabolome shifts between angiosperm and gymnosperm tree species, with angiosperms displaying greater concentrations of chlorophyll and amino acids alongside lower C/N ratios. These differences were also accompanied by discrepancies in an important set of secondary metabolites detected with the metabolomic technique. Furthermore, we also found that certain secondary compounds were essential in distinguishing between deciduous and evergreen species or families where targeted analysis could not detect significant differences. Our results indicate that temperate tree species may have conserved chemical 'fingerprints' that provide information on fundamental differences in the activity of certain plant metabolic pathways. This thus provides a promising tool to investigate how and why different plant species allocate C differently over the growing season and defend themselves against diverse abiotic and biotic pressures.</p>
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