Genetic differentiation and phenotypic plasticity in life-history traits between native and introduced populations of invasive maple trees

Genetically based phenotypic differentiation between native and invasive populations of exotic plants has been increasingly documented and commonly invoked to explain the success of some invasive species. Nonetheless, this basic information is lacking for invasive trees although they currently represent a major concern worldwide. Reciprocal common gardens were therefore set up in both native and introduced ranges of two exotic maple trees to assess the contribution of genetic differentiation and phenotypic plasticity to tree invasiveness. Almost 3,000 native and invasive seedlings of Acer negundo and Acer platanoides were planted in Canada and in France and their performances were compared in various life-history traits related to growth, leaf phenology and ecophysiology over 2 and 3 year periods. Invasive populations of A. negundo exhibited strong genetic differentiation in all the traits examined. Compared to their native conspecifics, they grew significantly larger in the introduced range and showed lower survival, reduced maximum assimilation rate and increased leaf area in the two gardens. They also expressed greater plasticity for growth and greater phenological sensitivity to temperature. Native and invasive populations of A. platanoides were plastic across environments but in contrast did not exhibit any genetic differentiation. This cross-continental comparison provides evidence that both genetic differentiation and phenotypic plasticity contribute synergistically to tree invasiveness. The influence of these respective processes depends on stage of invasion and the life-history strategy of each species. Plastic effects are likely more important during colonization and establishment whilst genetic effects may contribute more significantly during the spread of established populations

Adaptive evolution and phenotypic plasticity during naturalization and spread of invasive species: implications for tree invasion biology

Although the genetic aspects of biological invasions are receiving more attention in the scientific literature, analyses of phenotypic plasticity and genotype-by-environment interactions are still seldom considered in tree invasion biology. Previous studies have shown that invasions of tree species can be affected by intraspecific phenotypic plasticity, pre-adaptation, and post-introduction evolution, and we suggest there are opportunities for new developments in this field. Here, we present a description of the use of quantitative and molecular genetics in tree invasion biology, and propose an approach based on common garden experiments, quantitative and molecular genetic methods to investigate the role of adaptive evolution, phenotypic plasticity, and genotype-by-environment interactions in tree invasions, particularly at the infraspecific level. We illustrate the utility of this approach using examples from quantitative genetic studies of Pinus and an example from a classical reciprocal common garden experiment with Acer species. By using this approach, researchers can test hypotheses about the role and strength of genetic and environmental effects on population-level invasiveness and gain insights into evolutionary processes that occur during biological invasions. Moreover, knowledge of phenotypic plasticity and local adaption of tree populations may help researchers improve assessments of invasion risk

A comparison of five methods to assess embolism resistance in trees

Vulnerability to drought-induced embolism is a key trait that shapes drought resistance and that could be increasingly used to design climate-smart forest management guidelines and to anticipate the outcome of climate change on populations dynamics and ecosystems functioning. A panel of methods is currently available to measure embolism resistance. This makes crucial a proper identification of which methods are the most accurate for determining this trait. However, the measurement of embolism resistance is sensitive to numerous artifacts that may lead to large errors for a given species. In addition, not all methods are easily accessible because of the cost of some large equipment and/or certain lab facilities. The emergence of the easy and low cost Pneumatic method allows to perform vulnerability curves at high throughput. However, only few studies have evaluated the reliability of this method compared to others. In this study, we proposed a comparison of five methods that allowed to assess embolism resistance in eleven tree species with contrasting xylem anatomy and vessels length (six short vessel angiosperms, two tracheid bearing conifers and three long-vessel angiosperms), covering a large part of the range of embolism resistance observed in trees. Consistent results were obtained among all the methods for short-vessel angiosperm species. In tracheid-bearing conifers, the Pneumatic method overestimated vulnerability to embolism. In long-vessel species, the Pneumatic method led to inconsistent results with accurate vulnerability to cavitation curves (VCs) for one species but led to r-shaped VCs with a underestimation of incipient embolism for the two other ones. The comparison of VC parameters with turgor loss point is proposed as an indicator of the validity of the VCs. The conditions of validity, the advantages and pitfalls of the five methods are discussed. Our results warned against the widespread usages of some methods before rigorous validation tests have been performed