Influence des facteurs environnementaux sur la plasticité phénotypique et le microbiote : Étude expérimentale chez les broméliacées du genre Aechmea

Phenotypic plasticity, the ability of a genotype to produce different phenotypes in response to different environmental conditions, is a crucial mechanism for sessile organisms like plants that cannot escape their environment. The recent recognition of the role of microorganisms in plant health has led to considering them as potentially key players in plant-environment interactions, giving rise to the concept of the holobiont, the entity formed by a host and its microbial partners. The overall objective of this thesis is to explore the plasticity of plants at different levels of integration. To achieve this, we have leveraged the biological model represented by water-retaining bromeliads with two main objectives:Firstly, to characterize the phenotypic plasticity of bromeliads along environmental gradients by adopting a classic view of plant phenotype through the measurement of morpho-anatomical and physiological traits. In this part, we addressed the phenotypic plasticity of Aechmea aquilega at inter-individual and intra-organ scales.Secondly, we studied the phenotypic plasticity of the holobiont when exposed to different resource quantities. Plant phenotypes are strongly influenced by their microbiota, which are an integral part of the extended phenotype of the plant. In this second part, we expanded the study of plant traits by integrating the responses of microbial communities through metabarcoding approaches to better understand the holobiont system under environmental constraints. We also explored the putative role of the microbiota in transgenerational plasticity. For this purpose, we characterized transgenerational microbial fluxes and the influence of maternal environment on the phenotype and microbiota of offsprings in Aechmea mertensii.Our results refine our understanding of resource acquisition strategies in Bromeliads of the genus Aechmea, notably highlighting the significant contribution of root nutrition to their growth and complex responses within the same leaf to variations in light intensity. In the second part, we reveal a covariation between microbial communities and ecophysiological traits of Aechmea, supporting the existence of a coordinated response of the different constituents of the holobiont (i.e., microbiota and its host) to environmental variations. Finally, we demonstrate the existence of maternal effects influencing the phenotype and microbiota of offspring.The results of this work at the interface between microbiology and plant ecophysiology thus reveal a complex response of Aechmea plants to different environmental factors and biological scales (e.g., intra-organ, holobiont, and between generations). Phenotypic plasticity in plants appears to be the integration of various mechanisms and numerous interactions at different levels that need to be considered if we want to understand plant responses to past, present, and future environmental changes.La plasticité phénotypique, c'est-à-dire la capacité d'un génotype à produire différents phénotypes en réponse à différentes conditions environnementales, est un mécanisme crucial pour les organismes sessiles tels que les plantes, qui ne peuvent échapper à leur environnement. La reconnaissance récente du rôle des micro-organismes dans la santé des plantes a conduit à les considérer comme des acteurs potentiellement clés dans les interactions plantes-environnement, donnant naissance au concept d'holobiont, l'entité formée par un hôte et ses partenaires microbiens. L'objectif général de cette thèse est d'explorer la plasticité des plantes à différents niveaux d'intégration. Pour ce faire, nous avons exploité le modèle biologique représenté par les broméliacées retenant l'eau avec deux objectifs principaux :Premièrement, caractériser la plasticité phénotypique des broméliacées le long des gradients environnementaux en adoptant une vision classique du phénotype végétal par la mesure des traits morpho-anatomiques et physiologiques. Dans cette partie, nous avons abordé la plasticité phénotypique d'Aechmea aquilega aux échelles inter-individuelle et intra-organique.Deuxièmement, nous avons étudié la plasticité phénotypique de l'holobiont lorsqu'il est exposé à différentes quantités de ressources. Les phénotypes des plantes sont fortement influencés par leur microbiote, qui fait partie intégrante du phénotype étendu de la plante. Dans cette deuxième partie, nous avons élargi l'étude des caractéristiques des plantes en intégrant les réponses des communautés microbiennes par des approches de métabarcoding afin de mieux comprendre le système holobiont sous contraintes environnementales. Nous avons également exploré le rôle supposé du microbiote dans la plasticité transgénérationnelle. Pour ce faire, nous avons caractérisé les flux microbiens transgénérationnels et l'influence de l'environnement maternel sur le phénotype et le microbiote des descendants d'Aechmea mertensii.Nos résultats affinent notre compréhension des stratégies d'acquisition des ressources chez les Broméliacées du genre Aechmea, en mettant notamment en évidence la contribution significative de la nutrition racinaire à leur croissance et les réponses complexes au sein d'une même feuille aux variations d'intensité lumineuse. Dans la deuxième partie, nous révélons une covariation entre les communautés microbiennes et les traits écophysiologiques des Aechmea, soutenant l'existence d'une réponse coordonnée des différents constituants de l'holobiont (i.e., le microbiote et son hôte) aux variations environnementales. Enfin, nous démontrons l'existence d'effets maternels influençant le phénotype et le microbiote de la progéniture.Les résultats de ce travail à l'interface entre la microbiologie et l'écophysiologie végétale révèlent ainsi une réponse complexe des plantes Aechmea à différents facteurs environnementaux et échelles biologiques (par exemple, intra-organe, holobiont, et entre générations). La plasticité phénotypique chez les plantes semble être l'intégration de divers mécanismes et de nombreuses interactions à différents niveaux qui doivent être pris en compte si nous voulons comprendre les réponses des plantes aux changements environnementaux passés, présents et futurs

Light intensity mediates phenotypic plasticity and leaf trait regionalization in a tank bromeliad

International audienceBackground and Aims Phenotypic plasticity allows plants to cope with environmental variability. Plastic responses to the environment have mostly been investigated at the level of individuals (plants) but can also occur within leaves. Yet the latter have been underexplored, as leaves are often treated as functional units with no spatial structure. We investigated the effect of a strong light gradient on plant and leaf traits and examined whether different portions of a leaf show similar or differential responses to light intensity. Methods We measured variation in 27 morpho-anatomical and physiological traits of the rosette and leaf portions (i.e. base and apex) of the tank bromeliad Aechmea aquilega (Bromeliaceae) when naturally exposed to a marked gradient of light intensity. Key Results The light intensity received by A. aquilega had a strong effect on the structural, biochemical and physiological traits of the entire rosette. Plants exposed to high light intensity were smaller and had wider, shorter, more rigid and more vertical leaves. They also had lower photosynthetic performance and nutrient levels. We found significant differences between the apex and basal portions of the leaf under low-light conditions, and the differences declined or disappeared for most of the traits as light intensity increased (i.e. leaf thickness, adaxial trichome density, abaxial and adaxial trichome surface, and vascular bundle surface and density). Conclusions Our results reveal a strong phenotypic plasticity in A. aquilega, particularly in the form of a steep functional gradient within the leaf under low-light conditions. Under high-light conditions, trait values were relatively uniform along the leaf. This study sheds interesting new light on the functional complexity of tank bromeliad leaves, and on the effect of environmental conditions on leaf trait regionalization

Effect of substrate fertility on tank-bromeliad performances

International audiencePurpose: Members of the plant family Bromeliaceae can uptake nutrients directly from their leaves via leaf absorbing trichomes and their roots have long been reduced to anchorage function, thus overlooked. Recently, evidence has accumulated for a significant role for the roots of some species of tank bromeliads in both water and nutrients absorption. However, to date, little attention has been paid to the importance of the substrate fertility for the structure of the roots and the growth and performances of tank bromeliads.Methods: This study investigated the effect of substrate fertility on Aechmea aquilega regarding leaf and root traits, nutrient content, and growth. Seeds of this tank bromeliad were sowed in a greenhouse in French Guiana in three different substrates: a nutrient-poor, a nutrient-rich and a mixed substrate. The performances of 15-month-old A. aquilega were assessed by measuring leaf and root traits related to nutrient acquisition and resources capture.Results: We show that plants growing in nutrient-poor substrate grew twice slower and were smaller than plants grown on the nutrient-rich substrate with fewer leaves and roots, lower total dry mass, and smaller leaves and root length. Overall, 70% of measured traits responded significantly to the experimental treatments indicating that the response of A. aquilega to nutrient availability is a combination of physiological processes, leaf and root structure, and chemistry.Conclusion: This study is the first to show that the fertility of the substrate on which the bromeliad A. aquilega grows has a strong and lasting effect on the plant performances and may be a relevant factor for bromeliad ecolog

Effects of substrate quality on tank-bromeliad habitats and their freshwater organisms. ATBC Annual Meeting

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Environmental filtering and maternal effects on the phenotype of a neotropical bromeliad

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