Réponse du peuplier noir (Populus nigra L.) aux contraintes hydrogéomorphologiques : une expérimentation ex situ semi contrôlée

International audienceBased on the hypothesis of an eco-evolutionary feedback between woody riparian species and fluvial geomorphology, a semi-controlled ex situ experiment has been planned to quantify key response functional traits (morphological and biomechanical) of Populus nigra L. cuttings to simulated hydrogeomorphological constraints, as well as to dissociate the specific responses to them. The constraints tested are sediment burial and drag force exerted by floods. The characteristics of the experiment are presented as well as the experimental design. The hypothesis of a positive niche construction by P. nigra is tested to a certain degree. The results from this research will improve our understanding of riparian ecosystem functioning and specifically of the role of this key woody pioneer species within active floodplain rivers.Basé sur l’hypothèse d’existence d'une rétroaction éco-évolutive entre les espèces végétales riveraines ligneuses et la géomorphologie fluviale, une expérimentation ex situ en conditions semi-contrôlées a été planifiée afin de quantifier les traits de réponses fonctionnels (morphologique et biomécanique) de boutures de Populus nigra L. soumises à des contraintes hydrogéomorphologiques simulées : l’enfouissement sédimentaire, la force de traînée, et la combinaison des deux contraintes. Les questions scientifiques et le protocole expérimental sont présentés ici. L’hypothèse d’une construction de niche positive de P. nigra est testée à un certain degré. Les résultats de cette recherche contribueront à améliorer notre compréhension du fonctionnement des écosystèmes riverains et plus particulièrement du rôle de cette espèce ligneuse pionnière clé au sein de la bande active des cours d’eau

Determinants of photosynthetic light acclimation in hybrid walnut.

National audienc

Réponse des racines de peuplier noir aux contraintes hydrogéomorphologiques : une approche expérimentale

International audienceEven though it is well recognised that black poplar pioneer trees are riparian ecosystem engineers which modify their fluvial habitat, e.g. by enhancing sediment accumulation, the below-ground responses of young poplars to hydrogeomorphological constraints are still poorly understood. We performed a semi-controlled ex situ experiment to quantify key functional root traits of response of black poplar cuttings to simulated hydrogeomorphological constraints, i.e. drag force, sediment burial and their combination. The cuttings (n=128) were planted in woven polypropylene bags filled with sandy gravel and with an irrigation system attached, and assigned to one of the four possible treatments (1: drag force; 2: sediment burial; 3: drag force + sediment burial; 4: control). A completely randomized experimental design was employed with cuttings and treatments. The treatments were applied according to the seasonal occurrence and average duration of floods in the region where the genotype came from. The drag force treatment consisted in the application of three different bending levels on the plant to simulate the drag force exerted during one single flood. A continuous sequence of three floods of one week each was simulated. The sediment burial treatment consisted in the application of a 15 cm-layer of sandy sediment around the main stem to simulate the deposited sediment after a flood event. A destructive final harvest was performed at the end of one growing season. The below-ground morphology was characterised from manual measurements and image analysis using a trait-based approach. In order to test our hypothesis whether black poplar is able to modulate its phenotype when it is exposed to hydrogeomorphological constraints, we investigated the relationship between the different treatments and the morphology of the root system using directional and multivariate statistics. Our results show some differentiated trends and open up new perspectives for potential applications in bioengineering techniques and river restoration

Black poplar (Populus nigra L.) root response to hydrogeomorphological constraints: An experimental approach.

National audienceEven though it is well recognised that black poplar pioneer trees are riparian ecosystem engineers which modify their fluvial habitat, e.g. by enhancing sediment accumulation, the below-ground responses of young poplars to hydrogeomorphological constraints are still poorly understood. We performed a semi-controlled ex situ experiment to quantify key functional root traits of response of black poplar cuttings to simulated hydrogeomorphological constraints, i.e. drag force, sediment burial and their combination. The cuttings (n=128) were planted in woven polypropylene bags filled with sandy gravel and with an irrigation system attached, and assigned to one of the four possible treatments (1: drag force; 2: sediment burial; 3: drag force + sediment burial; 4: control). A completely randomized experimental design was employed with cuttings and treatments. The treatments were applied according to the seasonal occurrence and average duration of floods in the region where the genotype came from. The drag force treatment consisted in the application of three different bending levels on the plant to simulate the drag force exerted during one single flood. A continuous sequence of three floods of one week each was simulated. The sediment burial treatment consisted in the application of a 15 cm-layer of sandy sediment around the main stem to simulate the deposited sediment after a flood event. A destructive final harvest was performed at the end of one growing season. The below-ground morphology was characterised from manual measurements and image analysis using a trait-based approach. In order to test our hypothesis whether black poplar is able to modulate its phenotype when it is exposed to hydrogeomorphological constraints, we investigated the relationship between the different treatments and the morphology of the root system using directional and multivariate statistics. Our results show some differentiated trends and open up new perspectives for potential applications in bioengineering techniques and river restoration