Submitted to: Plant and Soil
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/17/2005
Publication Date: 2/1/2006
Citation: O'Dell, R.E., James, J.J., Richards, J.A. 2006. Congeneric serpentine and nonserpentine shrubs differ more in leaf ca:mg than in tolerance of low n, low p, or heavy metals. Plant and Soil Journal. 280:49-64. Interpretive Summary: Understanding plant adaptations to nutrient-poor soils is a critical step in identifying physiological traits that maximize food and forage production in harsh environments. We quantified growth, nutrient uptake and heavy metal storage in three pairs of closely related species grown in nutrient-poor serpentine soil. One species in each pair was endemic to serpentine soils. Results suggest that low nutrient requirements combined with the ability to selectively transport nutrients to shoots while storing toxic metals in roots are key evolutionary changes needed for survival on serpentine soils. By identifying these adaptations, these results will help scientist gain a better understanding of physiological traits that can increase production in nutrient-poor soils rich in heavy metals.
Technical 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 as well as greater allocation to leaves and less 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.