Evidence for Nutrient Biolifting in Hawaiian Climosequence Soils as Revealed by Alkaline Earth Metal Stable Isotope Systematics

Plants are known to scavenge nutrients such as phosphorus (P) from rock subtrates and concentrate those nutrients at the surface in order to satisfy long-term nutritional requirements. Using the stable isotope systematics of calcium (Ca), strontium (Sr) and barium (Ba) as proxy tracers, here we test the hypothesis that soils along a Hawaiian climosequence have “biolifted” P and other nutrients such as Ca from depth and concentrated those nutrients at the surface. Relative to isotope compositions in the volcanic soil parent materials, exchangeable Ca, Sr and Ba in the shallowest soils at sites having evidence for P biolifting are light confirming the role for plant uptake of these elements while exchangeable Ca, Sr and Ba of deeper soils at those sites are similar or heavy suggesting a complementary pool. In this pedogenic system Ca and Sr are more susceptible to leaching than Ba, thus Ba isotopes provide the most resilient evidence for biolifting across the climate gradient and a useful proxy for P biodynamics.