Soil influence on Cu and Co uptake and plant size in the cuprophytes Crepidorhopalon perennis and C. tenuis (Scrophulariaceae) in SC Africa

Cuprophytes are plants that mostly occur on Cu-rich soil in SC Africa. Crepidorhopalon perennis is endemic of a single site. C. tenuis has a broader niche, from normal to Cu-rich soil. Both have been considered as Cu-Co accumulators. We examined soil factors controlling heavy metal accumulation and plant fitness in natural populations. Plant mass and element concentrations in plants and soil were determined in 153 samples from five populations of C. tenuis on copper soil (CTC), two on normal soil (CTN) and the single population of C. perennis (CP). Soil in Cu-sites had higher concentrations of Ca, Mg, P, Mn, Zn, Cu, Co. Plants from Cu-sites were larger and had higher Cu and Co content, and lower Mg, Mn and Ca. Cu in shoots was influenced positively by Cu and Mn and negatively by Ca in the soil. Co in shoots was influenced positively by Co and negatively by Mn and Fe in the soil. Shoot mass was influenced positively by Cu and Mn (CT) or by Cu and Co (both species pooled) in the soil. The results suggest that C. tenuis and C. perennis are genuinely cuprophilous species. Large variation in metal accumulation in shoots can be accounted for by synergistic and antagonistic interactions among several heavy metals, yielding specific accumulation patterns in different populations.