Non-targeted root exudome profiling reveals genotype-specific strategies for phosphorus use from conventional and recycled sources

Phosphorus use efficiency (PUE) is a vital crop trait encompassing both acquisition and internal utilisation efficiencies. To address knowledge gaps in crop PUE and the growing application of phosphorus (P) recyclates, we investigated early growth and root exudation in sorghum genotypes. We tested the hypothesis that P-efficient landraces (SC283-14E and SC648-14E) outperform an inbred line (BTx623, bred under high-P conditions, with unknown PUE status) when supplied with less soluble P sources. Four P sources were applied, ranging from low to high solubility: rock phosphate (RP) < P recyclate hazenite (Haz) < single superphosphate (SSP) < mineral solution (MS). After 28 days of growth under low P supply, root exudates (125–2000 amu) were comprehensively profiled using FT-ICR-MS. Biomass production and P accumulation varied significantly among genotypes and P sources, with notable genotype × P source interactions. Compared to BTx623, SC283-14E produced greater root biomass with RP and higher total biomass with SSP, and accumulated more P with MS than the other genotypes. Genotype-specific exudates were identified across all P sources: phaseic acid (SC283-14E), flavonoids and/or polyphenols (SC648-14E), and amino acids and/or amino sugars (BTx623). Hazenite elicited the most distinct exudome profiles: SC283-14E released flavonoid dimers, tannins, and phenolic acid derivatives; SC648-14E exuded putative phenolic dimers and/or flavonoids; and BTx623 produced sulphur- and nitrogen-containing conjugates, including sulphonated peptides and amino acids. These findings highlight the potential of leveraging root exudate profiles in crop breeding for enhanced PUE in the circular phosphorus economy that recovers nutrients from agricultural, industrial, and food waste streams.