Strontium and calcium sorption and desorption from tomato roots

Calcium (Ca) is an essential plant nutrient responsible for many functions in plants, e.g., cell signaling and stress tolerance. The uptake pathway of Ca is shared by other elements like strontium (Sr), which shares many physicochemical similarities with Ca. Sr is a soil alkaline metal which if uptaken, negatively influences plant performance in the long term. Because of their shared characteristics, Sr was used for many years as a tracer of Ca. Even so, the degree of analogy between Sr and Ca in different plants tissues and between plants grown in different conditions is uncertain. Our previous work reported a high level of congruence between Sr and Ca in tomato plants grown in hydroponics. Nonetheless, we also reported a large initial variation between Sr and Ca soon after exposure. In our current work, tomato plants (Solanum lycopersicum L. 'Brigade') were grown in hydroponics and treated with different concentrations of Sr or Ca to describe the short-term behavior of Sr in different plants organs (with the emphasis on roots). The current study showed that Sr accumulates in different organs of the tomato plant with the following gradation: leaves > stems > roots. Additionally, Sr was adsorbed to the tomato roots with a high initial affinity, which caused a discrepancy between the initial removal of Sr and Ca from the solution when the exposure time was shorter than three hours. We believe that this work expands our grasp on the relationship between Sr and Ca, hopefully leading to a more precise utilization of Sr as the tracer of Ca.