Laminaria digitata Extract Improved Leaf Meristem Protection Under Drought and Nitrogen Uptake After Rehydration Through Hormesis-Based Chemical Priming in Lolium perenne.

Drought is among the most damaging stress for plants, impacting crop yield and grassland sustainability. This study aimed to evaluate the biostimulant effect of an algal extract from Laminaria digitata on Lolium perenne cultivated in a growth chamber. Leaves were sprayed at different concentrations 7 days before stopping irrigation. This priming period was followed by fourteen days of drought and ten days of recovery. Algal extract supplied at 2 and 5 L.ha^-1 stimulated nitrogen uptake during recovery, while higher doses were deleterious. During drought, algal extract 2 L.ha^-1 increased water content in leaves and shoot 0-3 cm housing the leaf meristems. The improvement in water content arose from the smaller decline in leaf relative water content (RWC), suggesting better osmotic adjustment. Cell membrane stability was less impaired during drought and quickly returned to pre-drought levels during recovery, indicating better membrane protection. The higher fructan content may contribute to osmotic adjustment and membrane protection. The results show that algal extract improved leaf meristem protection under drought and N uptake after rehydration through hormesis-based chemical priming. The treatment limited sucrose accumulation during drought, so that sucrose content can be used as an indicator of biostimulation together with RWC and cell membrane stability.