LAUSR

Bioactivities of eckol-type phlorotannins, i.e., eckol and EA6 (a fraction that contains 2-phloroeckol and dibenzodioxin-fucodiphloroethol), extracted from Ecklonia maxima, and a commercial seaweed biostimulant (Kelpak®) were investigated in white lupin and cucumber seedlings under different P-supplies. Lupin seedlings were grown with P-supplemented, P-free or P-free media with either eckol or Kelpak®. The cucumber seedlings were raised in hydroponic media with an insoluble salt of P as the sole P source and either supplemented with eckol, EA6, Kelpak® or no biostimulant. In the lupin seedlings, P starvation led to a reduction in root dry matter accumulation which was reversed when eckol or Kelpak® were applied. In cucumber seedlings, all the biostimulants significantly increased root dry matter but only eckol and Kelpak® induced total dry matter accumulation with Kelpak® also promoting shoot dry matter accumulation. In both lupin and cucumber seedlings, phlorotannins and Kelpak® elicited an increase in dry matter allocation to the roots. Eckol and Kelpak® elicited similar effects on cluster root development in lupin seedlings. All the biostimulants increased phosphatase activities in root exudates of lupin and cucumber seedlings. While tissue P contents were only augmented in Kelpak®-treated lupins, eckol, EA6 and Kelpak® treatments led to P-accumulation in the cucumber seedling leaves. The results showed that eckols influenced physiological traits linked to P-acquisition while Kelpak® altered both morphological and physiological traits for coping with P-limitation in both plants. The data suggest that eckol and seaweed biostimulants like Kelpak® may serve as sustainable tools for managing crops under P deprivation.