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The Salicaceae family comprises a large number of high-biomass species with remarkable genetic variability and adaptation to ecological niches. Salix caprea survives in heavy metal contaminated areas, translocates and accumulates Zn/Cd in leaves. To reveal potential selective effects of long-term heavy metal contaminations on the genetic structure and Zn/Cd accumulation capacity, 170 S. caprea isolates of four metal-contaminated and three non-contaminated middle European sites were analysed with microsatellite markers using Wright's F statistics. The differentiation of populations North of the Alps are more pronounced compared to the Southern ones. By grouping the isolates based on their contamination status, a weak but significant differentiation was calculated between Northern metallicolous and non-metallicolous populations. To quantify if the contamination and genetic status of the populations correlate with Zn/Cd tolerance and the accumulation capacity, the S. caprea isolates were exposed to elevated Cd/Zn concentrations in perlite-based cultures. Consistent with the genetic data nested anova analyses for the physiological traits find a significant difference in the Cd accumulation capacity between the Northern and Southern populations. Our data suggest that natural populations are a profitable source to uncover genetic mechanisms of heavy metal accumulation and biomass production, traits that are essential for improving phytoextraction strategies., (© 2010 Blackwell Publishing Ltd.)

In the present study, we have used PCR-RFLP markers to investigate the chloroplast DNA variation in 24 European populations of Salix caprea L. A subset of these populations has also been analysed with chloroplast microsatellites. The main feature of both markers is the absence of a clear geographic structure (G(ST(PCR-RFLP))=0.090, G(ST(microsatellites))=-0.017) and high levels of variation within populations. This lack of phylogeographic structure in S. caprea is suggested to be the consequence of the joint action of several factors: (i) presence of intermediate latitude refugia with large population sizes during the last glacial maximum, (ii) a high speed of recolonisation and dispersal ability, (iii) a high mutation rate and (iv) extensive hybridisation with other willow species. In addition to the S. caprea samples, a limited number of individuals from several other Salix species were also analysed with PCR-RFLP: S. cinerea, S. aurita, S. purpurea, S. atrocinerea, S. appendiculata, S. elaeagnos, S. fragilis and S. alba. Many of the haplotypes found in Salix caprea were also detected in S. cinerea, S. aurita, S. purpurea, S. atrocinerea and/ or S. appendiculata but not in S. alba, S. elaeagnos or S. fragilis. Our data suggest that hybridisation and gene flow have occurred within these two groups but not between them.