Assessment of bioavailability of polyphosphates and impacts on plant phosphorus uptake and phenotypes

Phosphorus (P) management in sustainable agriculture necessitates a comprehensive understanding of bioavailability and delivery mechanisms of various P species and the consequent impacts on crop growth. Polyphosphate (PolyP) has emerged to be a potentially significant, yet under-explored, P source with arising appreciation of its abundance and additional benefits to plants. This study investigated and compared the bioavailability of PolyP with orthophosphate (OrthoP) and other organic P species to hydroponically grown maize, as well as their effects in maize P uptake, partitioning and growth. Compared to OrthoP, PolyP supported maize growth with higher root-to-shoot ratios, improved phosphorus use efficiency (PUE), and enhanced P allocation to younger leaves, evidencing the distinctive impacts of P species and delivery on crop growth. Furthermore, in maize pre-treated with P starvation which presumably generated root exudates and metabolites, no distinctive differences on the maize growth were observed between PolyP and OrthoP, indicating the readily bioavailability of PolyP. This was further confirmed by dephosphorylation kinetics assessment of PolyP in comparison to two other organic P species, particularly in the presence of the common soil enzyme phytase or maize root exudates where PolyP dephosphorylation was greatly promoted. These results indicate that PolyP may offer relatively high bioavailability and efficiency as a P source and enhance plant growth and health. This research sheds light on the potential of implementing P recovery via the enhanced biological phosphorus removal (EBPR) technology that effectively bio-concentrates P as PolyP to meet the growing P demands and deepens the understanding of plant responses to different P forms, contributing to more sustainable P management strategies.