Differentiation of metallicolous and non-metallicolous Salix caprea populations based on phenotypic characteristics and nuclear microsatellite (SSR) markers

Abstract

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.

Figure 1

Foliar Zn (a) and Cd (b) concentration in S. caprea isolates derived from seven different populations. Boxes represent the median (vertical solid line), the arithmetic mean (vertical dashed line), and 25–75% percentile.Whiskers represent the 90th and 10th percentile. Significant differences were determined by a post hoc comparison of means (Scheffé test after nested anova; P < 0.05) and are indicated by different letters.

Figure 2

Total amount of leaf biomass per plant for S. caprea isolates derived from seven different populations. Boxes represent the median (vertical solid line), the arithmetic mean (vertical dashed line), and 25–75% percentile.Whiskers represent the 90th and 10th percentile. Significant differences were determined by a post hoc comparison of means (Scheffé test after nested anova; P < 0.05) and are indicated by different letters.

Figure 3

Correlation between total Zn and total Cd in leaves of the individual isolates (n = 132; r = 0.79; P < 0.001).

Figure 4

Relationship between the leaf biomass and the foliar Cd (A) and Zn (B) concentration.

Figure 5

Comparison of leaf biomass and Zn/Cd concentration of Salix caprea between isolates from Northern (N) and Southern (S) populations as well as between specimen from contaminated (C) and non-contaminated (N) sites. Error bars represent the standard error of the mean.A significant difference (P < 0.05) is indicated by an asterisk.