Invasive Acer negundo outperforms native species in non-limiting resource environments due to its higher phenotypic plasticity

<p>Abstract</p> <p>Background</p> <p>To identify the determinants of invasiveness, comparisons of traits of invasive and native species are commonly performed. Invasiveness is generally linked to higher values of reproductive, physiological and growth-related traits of the invasives relative to the natives in the introduced range. Phenotypic plasticity of these traits has also been cited to increase the success of invasive species but has been little studied in invasive tree species. In a greenhouse experiment, we compared ecophysiological traits between an invasive species to Europe, <it>Acer negundo</it>, and early- and late-successional co-occurring native species, under different light, nutrient availability and disturbance regimes. We also compared species of the same species groups <it>in </it><it>situ</it>, in riparian forests.</p> <p>Results</p> <p>Under non-limiting resources, <it>A. negundo </it>seedlings showed higher growth rates than the native species. However, <it>A. negundo </it>displayed equivalent or lower photosynthetic capacities and nitrogen content per unit leaf area compared to the native species; these findings were observed both on the seedlings in the greenhouse experiment and on adult trees <it>in situ</it>. These physiological traits were mostly conservative along the different light, nutrient and disturbance environments. Overall, under non-limiting light and nutrient conditions, specific leaf area and total leaf area of <it>A. negundo </it>were substantially larger. The invasive species presented a higher plasticity in allocation to foliage and therefore in growth with increasing nutrient and light availability relative to the native species.</p> <p>Conclusions</p> <p>The higher level of plasticity of the invasive species in foliage allocation in response to light and nutrient availability induced a better growth in non-limiting resource environments. These results give us more elements on the invasiveness of <it>A. negundo </it>and suggest that such behaviour could explain the ability of <it>A. negundo </it>to outperform native tree species, contributes to its spread in European resource-rich riparian forests and impedes its establishment under closed-canopy hardwood forests.</p

Stakeholders' views on the global guidelines for the sustainable use of non‐native trees

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversity, ecosystem functions and human well‐being. To help minimize the negative impacts and maximize the economic benefits of NNTs, Brundu et al. developed eight guidelines for the sustainable use of NNTs globally—the Global Guidelines for the Use of NNTs (GG‐NNTs). Here, we used an online survey to assess perceptions of key stakeholders towards NNTs, and explore their knowledge of and compliance with the GG‐NNTs. Our results show that stakeholders are generally aware that NNTs can provide benefits and cause negative impacts, often simultaneously and they consider that their organization complies with existing regulations and voluntary agreements concerning NNTs. However, they are not aware of or do not apply most of the eight recommendations included in the GG‐NNTs. We conclude that effectively managing invasions linked to NNTs requires both more communication efforts using an array of channels for improving stakeholder awareness and implementation of simple measures to reduce NNT impacts (e.g. via GG‐NNTs), and a deeper understanding of the barriers and reluctance of stakeholders to manage NNT invasions. Read the free Plain Language Summary for this article on the Journal blog

Using automated sanding to homogeneously break seed dormancy in black locust (Robinia pseudoacacia L., Fabaceae)

Physical dormancy of Robinia pseudoacacia seeds makes it a challenge for scientists and forest managers to obtain a homogeneous germination for larger seed samples. Water imbibition of the seeds can be achieved through manual piercing of the seed coat, but this method remains time consuming and heterogeneous. We tested several ecologically friendly methods to break seed dormancy, including manual pin puncture, water soaking, oven dry-heating (two temperatures) and sanding. Sanding was performed using an automatic grinder to control shaking duration (three durations) and get a homogeneous scraping of the coat. All methods, except dry-heating, resulted in successful dormancy breaking; water soaking was the least efficient method, attaining 57% germination. Sanding proved to be as efficient as puncturing (97%) but long duration sanding (10 or 15 min) could damage cotyledons, which would impede further development of the plant. Short-time sanding (5 min) proved to be the best method to reach high total germination and healthy (undamaged cotyledon) seedlings, and was successfully applied to 500 seeds. The reference puncture method and the automatic sanding were also tested on seeds of nine Fabaceae species and proved to be efficient for some species. Automated sanding can thus be used as a standard to break physical dormancy of black locust or other Fabaceae seeds to allow further comparative studies of plant populations or genotypes

The phyllosphere: microbial jungle at the plant–climate interface

The surface of plant leaves, or the phyllosphere, harbors hyperdiverse microbial communities. These communities ediate foliar functional traits, influence plant fitness, and contribute to several ecosystem functions, including nutrient and water cycling. In this review, we briefly recall the history of phyllosphere research and present the features of this microbial habitat. Adopting a recent framework for evolutionary community ecology, we then review evidence for each of the four major processes shaping phyllosphere microbial communities: dispersal, evolutionary diversification, selection, and drift. We show how these processes are influenced by the host plant, the surrounding atmospheric conditions, and microbial interactions. Rapidly growing evidence indicates that phyllosphere microbial communities are altered by global change, with potential cascading effects on plant performance, plant evolution, and ecosystem functioning. We propose future avenues for phyllosphere research aimed at improving plant adaptation and ecosystem resilience to environmental changes

Self-shading affects allometric scaling in trees

West et al. [Science, 284 (1999) 1677] derived an optimal body-size scaling exponent under the assumption that resources are evenly distributed among exchange surfaces, leading to the well-known ¾ scaling rule. In trees, this implies a volume-filling branching network (a fractal dimension of 3 for foliage). However, there is evidence that the fractal dimension is less than 3 in trees. Here, we include self-shading in the derivation of optimal fractal dimensions. With self-shading, resources are not evenly distributed among leaves because light enters the crown at the surface and is gradually attenuated within the crown. We find that the optimal fractal dimension can take values between 2 and 3, depending on light interception properties and crown size. For a large data set on foliage and woody biomass in gymnosperm trees, we confirm that the fractal dimension of foliage is less than 3, and that it shows a weak dependence on crown size. However, foliage biomass scaled with crown woody biomass with an exponent of 0·78, very close to the theoretical expectation of ¾ scaling. This can be explained by a deviation from the theoretical prediction in the scaling of crown woody biomass and crown length. Overall, these results confirm a deviation from volume filling in gymnosperm trees, and we provide an explanation for this deviation in terms of optimal metabolic scaling. Because ¾ scaling of foliage biomass is still approximately valid, this implies that metabolic scaling exponents may not be as tightly linked to the fractal dimension of foliage as previously assumed

Relative Distance Plasticity Index (RDPI) along a nutrient gradient for populations of <i>Acer negundo</i> from the native and invasive ranges.

<p>Comparisons of RDPI using a Generalized Linear Mixed Model with range as a fixed factor and population nested within range as a random factor. Significant difference between ranges (<i>P</i><0.05) denoted by an asterisk. See text for definition of terms.</p

Plasticity of native and invasive seedlings of <i>Acer negundo</i> to nutrient availability.

<p>Means ± SE of traits related to growth (A,B), physiology (C,D), leaf morphology (E), biomass (F,G) and biomass allocation (H) are represented. n = 192 (height and diameter), 32 (<i>A</i>_area) and 48 (N_area, LMA, <i>W</i>_t and <i>A</i>_l) per range and nutrient level. See text for definition of terms.</p