Phosphorus limitation enhances the production and release of allelochemicals: Dynamics of oxylipins in estuarine bloom-forming diatoms.

Excessive nitrogen inputs have intensified phosphorus (P) limitation in estuarine by raising the N:P ratio, yet the dynamics and potential ecological effects of diatom-derived allelochemicals under P-stress remain unclear. Combining field surveys at core station S in the Hanjiang River estuary with controlled laboratory experiments, we investigated how P-limitation regulates polyunsaturated aldehydes (PUAs) production and release in bloom-forming diatoms. Field blooms at Station S were dominated by PUA-producing diatoms such as Skeletonema spp., with particulate and dissolved PUAs at 0.6 nmol L-1 and 0.03 nmol L-1, respectively. Seven diatom strains were isolated via N/P-enriched culture, among which Skeletonema costatum B6 exhibited relatively higher PUA accumulation (1.8-2.8-fold that of conspecific strains) and was selected as the representative strain for subsequent laboratory incubation experiments. Under physiological P-limitation, particulate PUAs concentrations increased by 65.4% (1.7× per-cell content) relative to controls, showing a clear dose-response: negatively correlated with phosphate and positively with N/P ratio. PUAs were released through a phased mechanism, characterized by a synchronized, massive release during the stationary phase prior to major cell lysis, followed by passive leakage during culture decline. Notably, this study observed a temporal coupling between the release of dissolved PUAs and the recovery of dissolved inorganic phosphorus, shedding light on the potential linkage and working hypothesis between allelochemicals and endogenous phosphorus cycling. We present a "stress response-production-release" framework under physiological P-stress, providing mechanistic insights into bloom-forming diatom allelopathic dynamics in high-N/P estuaries.