3.3 Heavy metal uptake and tolerance in C. purpureus: common garden experiment
The total concentrations of Cd and Cu in the soil where we collected Cp1 were 0.39 ± 0.07 and 15.9 ± 4.7 µg g-1 respectively. Total concentrations of Cd and Cu increased significantly in Cd- and Cu-treated plants (χ²treatment = 7.5, p < 0.01 for Cd; χ²treatment = 8.31, p < 0.01 for Cu; Fig. 4A, E). The relative levels of both metals increased significantly in almost all populations as indicated by the significant effect of the treatment (χ²treatment = 2.06, p < 0.001 for Cu; χ²treatment = 6.88, p < 0.0001 for Cd; Fig. 4B, F). The “Population by Treatment” interaction was significant only for Cu (χ²pop:treat = 1.07, p<0.05) as Cu-treated plants did not accumulate more Cu than control plants for Cp1. Exposure to these metals caused a significant decrease in protonemal growth in all three populations (χ²treatment= 2.31, p < 0.0001 for Cu; χ²treatment = 98.50, p < 2.2e-16 for Cd; Fig. 4C, G) although the magnitude of the effect differed among populations as indicated by the significant “Population by Treatment” interaction (χ²pop:treat = 33.20, p < 0.0001 for Cu; χ²pop:treat = 8.21, p < 0.0001 for Cd). Thus, whereas the mean size of the protonemal mat of Cu-treated plants of Cp1 decreased by 17%, it decreased by 47 and 59% in Cp2.m and Cp2.f respectively. For Cd, the mean size of the protonemal mats decreased by 53, 74 and 26% in Cd-treated plants from Cp1, Cp2.m and Cp2.f respectively.
Cu treatment did not have a significant effect in oxidative damage as measured by the concentrations of MDA. However, Cd treatment showed a significant effect and this effect differed across populations (χ²pop:treat = 3.60, p < 0.0001) with males from Cp2 (Cp2.m) experiencing more damage than Cp1 and females from the same population (Cp2.f).