Eckols and seaweed-biostimulant (Kelpak®) improve adaptative responses for phosphorus acquisition in white lupin and cucumber seedlings under phosphorus deficiency

Abstract 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.