Cu isotopic compositions in Elsholtzia splendens: Influence of soil condition and growth period on Cu isotopic fractionation in plant tissue

• Remobilization of Cu has a considerable influence on Cu isotopic fractionation within plant.
• Oxidation reaction occurs at the root–stem interface in E. splendens.
• Convection controls Cu transport in stem and branch of E. splendens.
• δ65Cu in xylem and phloem should be different.

This study investigates the magnitude and direction of Cu isotopic fractionation in the Cu-tolerant, strategy I plant, Elsholtzia splendens, considering the effect of soil condition and plant growth cycle. Uptake of Cu by E. splendens from soil was found to favor light Cu isotopic enrichment (δ65Cu < 0‰) due to reduction at the soil–root interface. The magnitude of fractionation between soil and plant was found to be dependent on free Cu ion species in soil solution correlated with pH value of soil other than the phytoavailable component of soil or total soil for the same parent soil.Cu isotopic fractionation occurs in plant, the fractionation direction and magnitude would vary between different plant organs (i.e., root and stem) as well as different plant tissues (i.e., xylem and phloem). Remobilization of Cu associated with plant senescence was found to have a considerable effect on Cu isotopic fractionation within the plant, and the fractionation factor was found to change with the degree of remobilization. Overall, the results show that the Cu isotopic composition is useful as a tracer for probing the mechanisms of Cu translocation and retranslocation between soil and plants, and within plants.