Foliar vs. soil application of Ascophyllum nodosum extracts to improve grapevine water stress tolerance

Biostimulants have recently been used in sustainable agriculture systems to improve plant growth and resilience to biotic and abiotic stress. In this study, foliar (ANEfl) and soil (ANEsl) A. nodosum extract applications were studied to elucidate the impact of different delivery methods on grapevines physiology either under well-watered conditions (WW) or under a water deficit period and a subsequent water recovery (WS). ANEfl increased leaf soluble sugars and photosynthesis of WW vines. Under progressive WS conditions, ANEfl positively impacted leaf gas exchange and water use efficiency (+35 % as compared to untreated vines) at Ψstem about -0.65 MPa. Photosynthesis was also improved during the re-watering period (+2.7 μmol CO2 m−2 s-1) via preserved photochemical efficiency (Fv/Fm +0.19 as compared to untreated vines) and enhanced leaf anatomical and biochemical traits (+8% leaf dry matter and +27.3 mg/g DW of leaf soluble sugars). Contrarily, when soil applied, A. nodosum extracts did not significantly improve vine physiology during the reduced water supply period and only mild effects were detected at re-watering. Results demonstrates that foliar applications of A. nodosum extracts could be an alternative sustainable tool to improve grapevine physiological performances under mild-to-moderate water deficit and to preserve photosystems integrity and vineyard resilience when water limiting conditions get more severe.