Stable strontium isotope fractionation in hydroponically grown mung and soy bean sprouts

This study investigated whether stable strontium isotope (⁸⁸Sr/⁸⁶Sr) fractionation occurs during nutrient uptake by bean plants. Mung and soy beans were cultivated hydroponically using two nutrient solutions with different strontium (Sr) isotope compositions. The Sr and calcium (Ca) concentrations, ⁸⁷Sr/⁸⁶Sr ratios and δ^88/86Sr values of the seeds, organs, initial nutrient solutions, and residual nutrient solutions were measured. The triple Sr isotope plot illustrates that bean sprout organs deviated considerably from the binary end-member mixing lines between intact bean seeds and the initial nutrient solutions, indicating fractionation of δ^88/86Sr. In addition, the residual nutrient solutions had heavier δ^88/86Sr values than the initial nutrient solutions, further supporting preferential uptake of lighter Sr isotopes by bean sprouts. This study indicates that stable Sr isotope fractionation occurs during nutrient uptake by bean plants, and that controlled hydroponic experiments are highly effective for observing this process.