Split phosphorus application strategies in calcareous soil enhance hyperaccumulator growth without compromising cadmium uptake

Enhancing hyperaccumulator biomass without compromising metal uptake remains a critical challenge in phytoremediation. This study investigated the effects of split phosphorus (P) fertilization on cadmium (Cd) extraction by Solanum alatum Moench in calcareous soil. Phosphorus was applied either fully as basal fertilizer (control) or split into 50 % basal and 50 % top dressing during seedling, flowering, and fruit-setting stages at ratios of 0:1:0, 1:1:1, and 1:2:1. Split P application increased shoot dry biomass by 6.1–26.9 % compared to the control, without altering shoot P concentration, indicating efficient fertilization. Soil phytase activity surged by 415 % during flowering in the treatment with the lowest fertilization level at this stage, suggesting enhanced organic P mineralization. Concurrently, active calcium carbonate concentration decreased by 10.7–12 %, reducing Cd retention and elevating soil bioavailable Cd by 7.6–62 %. Despite biomass dilution, shoot Cd uptake remained stable, ultimately increasing shoot Cd extraction by 10.4–26.1 %. These results demonstrate that split P application amplifies Cd phytoextraction in calcareous soils through dual mechanisms: direct biomass stimulation and indirect Cd mobilization via organic P mineralization and calcium carbonate suppression.