genetic differentiation; phenotypic plasticity; northern red oak
Abstract :
[en] We investigated the role of interaction between environmental conditions and genetics in the success of tree invasion. Indeed, invasiveness is expressed only under certain environments: for example, European populations of Acer negundo L. present higher growth and a longer growing season length explained by earlier budburst compared to that of U.S. populations of A. negundo. This may be related to rapid changes in introduced populations. Provenance tests are appropriate tools for studying genetic differentiation by comparing populations of different origins under several environmental conditions. Northern Red Oak (Quercus rubra) which was first introduced from USA to France as an ornamental species has received a strong interest in forestry since the late 19th century. This interest prompted the installation of comparative trials to establish a breeding program during the 80s-90s at the demand of forest managers. Recently, European forest managers seek to evaluate its invasiveness and to limit its natural expansion that impedes the regeneration of sessile or pedunculate oaks. Two provenance trials have been settled in South-West and North-East of France, containing 66 American and 60 European provenances, corresponding to 40000 trees per trial, which were followed between 1982 and 2012 on traits related to fitness. Within each trial, differences between ranges would reflect the existence of genetic differentiation between populations, while differences between trials would indicate the existence of phenotypic plasticity. Statistical analyses showed the existence of genetic differentiation, invasive European populations demonstrating superior growth compared to native populations. Regarding phenology, the results are inconclusive, probably due to the strong inter-annual variability of these traits and the availability of a single measurement. A monitoring of leaf and fruiting phenology, traits heavily involved in the determination of fitness, are thus required. On the other hand, in order to evaluate the adaptive nature of these differentiations, analyses of diversity molecular markers will also be undertaken.
