Congeneric Serpentine and Nonserpentine Shrubs Differ More in Leaf Ca:Mg than in Tolerance of Low N, Low P, or Heavy Metals

Abstract

Serpentine soils limit plant growth by NPK deficiencies, low Ca availability, excess Mg, and high heavy metal levels. In this study, three congeneric serpentine and nonserpentine evergreen shrub species pairs were grown in metalliferous serpentine soil with or without NPKCa fertilizer to test which soil factors most limit biomass production and mineral nutrition responses. Fertilization increased biomass production and allocation to leaves while decreasing allocation to roots in both serpentine and nonserpentine species. Simultaneous increases in biomass and leaf N:P ratios in fertilized plants of all six species suggest that N is more limiting than P in this serpentine soil. Neither N nor P concentrations, however, nor root to shoot translocation of these nutrients, differed significantly between serpentine and nonserpentine congeners. All six species growing in unfertilized serpentine soil translocated proportionately more P to leaves compared to fertilized plants, thus maintaining foliar P. Leaf Ca:Mg molar ratios of the nonserpentine species were generally equal to that of the soil. The serpentine species, however, maintained significantly higher leaf Ca:Mg than both their nonserpentine counterparts and the soil. Elevated leaf Ca:Mg in the serpentine species was achieved by selective Ca transport and/or Mg exclusion operating at the root-to-shoot translocation level, as root Ca and Mg concentrations did not differ between serpentine and nonserpentine congeners. All six species avoided shoot toxicity of heavy metals by root sequestration. The comparative data on nutrient deficiencies, leaf Ca:Mg, and heavy metal sequestration suggest that the ability to maintain high leaf Ca:Mg is a key evolutionary change needed for survival on serpentine soil and represents the physiological feature distinguishing the serpentine shrub species from their nonserpentine congeners. The results also suggest that high leaf Ca:Mg is achieved in these serpentine species by selective translocation of Ca and/or inhibited transport of Mg from roots, rather than by uptake/exclusion at root surfaces.

Arbuscular mycorrhizal symbiosis on serpentine soils: the effect of native fungal communities on different Knautia arvensis ecotypes

“…Numerous studies have shown differences in Mg and Ca uptake by serpentine and non-serpentine populations of the same plant species when grown in a serpentine substrate (e.g., Johnston and Proctor 1981;O"Dell et al 2006;Sambatti and Rice 2007). Higher Ca and lower Mg uptake, resulting in significantly higher shoot Ca/Mg ratios, have frequently been recorded for serpentine plants, suggesting that selective Ca accumulation and Mg exclusion and/or sequestration by roots are important evolutionary adaptations of serpentine species (O"Dell et al 2006;Kazakou et al 2008).…”

“…Higher Ca and lower Mg uptake, resulting in significantly higher shoot Ca/Mg ratios, have frequently been recorded for serpentine plants, suggesting that selective Ca accumulation and Mg exclusion and/or sequestration by roots are important evolutionary adaptations of serpentine species (O"Dell et al 2006;Kazakou et al 2008). In the present experiment, a direct comparison of Ca and Mg uptake in serpentine and non-serpentine populations of K. arvensis was not possible due to their cultivation in native substrates that differed in available Ca and Mg concentrations.…”

Small-scale diversity of plant communities and distribution of species niches on a copper rock outcrop in Upper Katanga, D.R.Congo

“…Communities with a high level of soil Cu (I, II, III) also differed in other parameters including nutrients. Metallicolous communities associated with higher nutrient concentrations than other communities, differ from those on serpentine soils, where deficiency of N, P, K and Ca has been suggested as a potential reason for limited plant productivity (Kruckeberg 1984, O'Dell et al 2006. Communities with a lower Cu contamination (IV, V) also differed from each other notably in Fe and Mg.…”

Chemical soil factors influencing plant assemblages along copper-cobalt gradients: implications for conservation and restoration

“…Similar patterns are observed in eastern parts of the Katangan Copperbelt (unpublished data). This, however, differs from serpentine soils where deficiency in NPK and Ca has been suggested as a potential reason for the limited plant productivity (Kruckeberg 1984;O'Dell et al 2006;Proctor 1971;Whittaker 1954). While poorer in number of species per 1 m 2 , Steppes host a larger number of endemics with higher occurrences per 1 m 2 .…”