Structural blueprint and ontogeny determine the adaptive value of the plastic response to competition in clonal plants: a modelling approach

International audienceLocal competitive interactions strongly influence plant community dynamics. To maintain their performance under competition, clonal plants may plastically modify their network architecture to grow in the direction of least interference. The adaptive value of this plastic avoidance response may depend, however, on traits linked with the plant's structural blueprint and ontogeny. We tested this hypothesis using virtual populations. We used an Individual Based Model to simulate competitive interactions among clones within a plant population. Clonal growth was studied under three competition intensities in plastic and non-plastic individuals. Plasticity buffered the negative impacts of competition at intermediate densities of competitors by promoting clone clumping. Success despite competition was promoted by traits linked with (1) the plant's structural blueprint (weak apical dominance and sympodial growth) and (2) ontogenetic processes, with an increasing or a decreasing dependence of the elongation process on the branch generation level or length along the competition intensity gradient respectively. The adaptive value of the plastic avoidance response depended on the same traits. This response only modulated their importance for clone success. Our results show that structural blueprint and ontogeny can be primary filters of plasticity and can have strong implications for evolutionary ecology, as they may explain why clonal plants have developed many species-specific plastic avoidance behaviours

How Past and Present Influence the Foraging of Clonal Plants?

Clonal plants spreading horizontally and forming a network structure of ramets exhibit complex growth patterns to maximize resource uptake from the environment. They respond to spatial heterogeneity by changing their internode length or branching frequency. Ramets definitively root in the soil but stay interconnected for a varying period of time thus allowing an exchange of spatial and temporal information. We quantified the foraging response of clonal plants depending on the local soil quality sampled by the rooting ramet (i.e. the present information) and the resource variability sampled by the older ramets (i.e. the past information). We demonstrated that two related species, Potentilla reptans and P. anserina, responded similarly to the local quality of their environment by decreasing their internode length in response to nutrient-rich soil. Only P. reptans responded to resource variability by decreasing its internode length. In both species, the experience acquired by older ramets influenced the plastic response of new rooted ramets: the internode length between ramets depended not only on the soil quality locally sampled but also on the soil quality previously sampled by older ramets. We quantified the effect of the information perceived at different time and space on the foraging behavior of clonal plants by showing a non-linear response of the ramet rooting in the soil of a given quality. These data suggest that the decision to grow a stolon or to root a ramet at a given distance from the older ramet results from the integration of the past and present information about the richness and the variability of the environment

La clonalité : un processus majeur de la dynamique spatiale et du fonctionnement des communautés végétales en systèmes prairiaux

Dispersion through clonal growth may be a major process of plant community structuring especially in grassland systems where most species are clonal. These species produce genetically identical ramets organized in a network structure, whose aggregation depends on the species clonal growth strategy. The present thesis aims at analyzing and understanding grassland plant community dynamics based on spatial assembly rules of clonal species and determining its consequences for community functioning. To achieve these goals, we used complementary experimental and modeling approaches. We demonstrated that clonal growth strategies determine community spatial structure at fine scale, generating a wide range of patterns. This variability was suggested to result from a modification of clonal traits in response to the biotic environment. Indeed, we demonstrated that clones are able to adjust horizontal growth based on competitor's identity. The adaptive nature of this plastic response in resistance to competition depended on plant structural blue-print and, to a lesser extent, on ontogeny. We also demonstrated that clonal traits had a major role in community functioning by influencing productivity, probably through the spatial patterns they drive. These results were applied to the establishment of herbaceous buffer strips and helped to define an optimal sowing to maximize water preservation. The present thesis underlines the importance of spatial processes operating at the clone scale for those operating at the community or the ecosystem scale.La dispersion par croissance clonale serait un processus majeur de la structuration des communautés végétales, particulièrement en prairies où une majorité d'espèces sont clonales. Celles-ci produisent des modules génétiquement identiques organisés en réseau, dont l'agrégation dépend de la stratégie de croissance de l'espèce. Cette thèse vise à analyser et à comprendre la dynamique des communautés végétales de prairie en se basant sur les règles d'assemblage spatial des espèces clonales et d'en déterminer les conséquences pour leur fonctionnement. Pour cela, des approches complémentaires expérimentales et de modélisation ont été utilisées. Nos résultats montrent que les stratégies de croissance des clones déterminent la structure spatiale des communautés à échelle fine, générant un large panel de patrons. Le patron spatial d'une espèce varie selon les stratégies de croissance clonale présentes dans la communauté. Ces variations résulteraient d'une modification des traits clonaux en réponse à l'environnement biotique. Le clone est capable d'ajuster sa croissance horizontale selon l'identité de son compétiteur grâce aux informations collectées par les modules. La valeur adaptative de cette réponse plastique dans la résistance à la compétition dépend du structural blue-print de la plante mais peu de l'ontogénie. Nous montrons également que les traits clonaux ont un rôle majeur dans le fonctionnement des communautés en influençant leur productivité, probablement via les patrons spatiaux qu'ils génèrent. Ces résultats ont été utilisés dans le cadre de la mise en place des bandes enherbées, afin de définir un semis optimal par rapport à leur fonction de préservation de la qualité de l'eau. Ce travail souligne l'importance des processus spatiaux observés à l'échelle du clone pour ceux opérant à l'échelle de la communauté ou de l'écosystème

Effect of current and past neighborhood composition on plant response to competition

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Plant traits respond to the competitive neighbourhood at different spatial and temporal scales

International audienceBackground and Aims Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan. Methods Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5–25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively. Key Results Most of the measured traits of E. repens responded to the local neighbourhood (5–10 cm radius), with an additional effect of the larger neighbourhood (20–25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundanceof specific species. Conclusions This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms

New insights from multidimensional trait space responses to competition in two clonal plant species

International audience1. Trait intraspecific variability determines community dynamics and species coexistence. In response to competition, plants can display intraspecific variability to enhance their competitive ability or stabilise their niche differences with competitors. This response is multidimensional because it involves changes along different functional axes and inevitable trade‐offs between traits. Here, we transposed the recent concept of the multidimensional trait space to the analysis of intraspecific plant response to competition. We specifically tested the following: (a) in the absence of competitors, the plant multidimensional trait space will be packed towards strategies promoting plant colonisation; and (b) with competitors, the plant multidimensional trait space will be directed towards competition with its size and shaping characteristics dependent on competitor species richness.2. We studied trait intraspecific variability of two clonal species, Brachypodium pinnatum (L.) P. Beauv. and Elytrigia repens (L.) Gould, in response to competition. We analysed plant response in the absence of competitors and in competition. Competition treatments included intraspecific and interspecific experimental mixtures with increasing species richness. For each target species and each treatment, we built an hypervolume based on six traits involved in the three‐dimensional competition (i.e., ramet and connection traits). We measured these hypervolumes for their size, similarity and the contribution of traits in their shaping.3. In the absence of competitors and for both species, we demonstrated a multidimensional trait space packing towards a colonisation strategy. Under competition, the multidimensional trait spaces of the two target species were the widest at the extremes of the richness gradient, that is, intraspecific and interspecific high richness competition treatments. High intraspecific variability either promoted niche differentiation from individuals of similar species or reflected the large range of competitive responses deployed when plants were faced with many different competitor identities. The multidimensional response process was based on fine adjustments of various traits depending on the surrounding neighbourhood composition and more specifically, on the competitor functional similarity with the target species.4. This study emphasises the multidimensionality of species competitive response, and also underlines the so far neglected importance of competitor species richness for trait intraspecific variability and subsequently community assembly

Effect of clonal colonization strategy on productivity in plant communities: a wide-scale mesocosm experiment

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Clonal traits outperform foliar traits as predictors of ecosystem function in experimental mesocosms

International audienceQuestions: Is productivity linked with clonal traits through their indirect effect on competitive interactions? Are clonal traits better predictors of productivity than foliar traits? Location: Rennes, France. Methods: We used a wide-scale mesocosm experiment based on several assemblages of species differing in clonal traits, and evaluated if the relationship between biomass production and clonal traits is consistent at different ecological scales. Results: Results showed that at the individual level, foliar traits were independent from clonal traits in most studied species. Community specific above-ground net primary productivity was significantly correlated to community-aggregated values of clonal and foliar traits. Nevertheless, a stronger relationship with clonal traits was indicated, emphasizing a plant foraging strategy along the horizontal plant plane, which was a determinant of community productivity. An inverse relationship between clonal traits and biomass production was observed at the individual and community levels, which was attributed to modifications in resource acquisition processes resulting from competitive interactions. Conclusions:We demonstrated that clonal traits are correlated with productivity at the individual and community scales. These traits were indicators of resource acquisition processesmediated through competitive interactions

Do Dialytrichia mucronata and D. saxicola Share the Same Ecological Preferences?A Case Study in the Rhône Valley (France) and Possible Application for River Incision Biomonitoring

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