Effective phytoremediation depends on plant species that combine high biomass production with efficient P accumulation and tolerance to elevated nutrient loads. Therefore, this study aimed to compare the P removal efficiency (PRE), uptake capacity, and toxicity threshold among four Azolla samples from three species (A. pinnata, A. caroliniana, and A. filiculoides) grown under in high-P media. Growth responses, P, Fe, N, and Zn content, and PRE were measured. All species showed similar growth and P uptake responses up to 5 mM P. Beyond this concentration, species-specific responses were observed: A. pinnata became toxic and died while A. filiculoides (Utr.) tolerated up to 25 mM. In contrast, A. caroliniana and A. filiculoides (Can) maintained stable growth even under higher P exposure conditions, despite no further increase in tissue P concentration. This pattern suggests a regulated response to P accumulation, rather than dilution or luxury consumption (nutrient uptake and accumulation beyond required levels without further increase in biomass). P removal efficiency decreased significantly at concentrations above 5 mM and remained unchanged at higher P supplies, indicating that the contaminant concentration significantly affects the removal efficiency. Overall, the results indicate significant inter- and intra-specific variation in P toxicity, uptake and removal in Azolla. Therefore, this highlights the importance of selecting the appropriate species and considering contaminant concentration for efficient phytoremediation.
Hamzehei et al. (Fri,) studied this question.