Deciphering Early Biostimulant-Induced Metabolic Reprogramming in Young Olive Trees (Olea europaea L.) Through GC/EI/MS Metabolomics

Abstract

Olive tree (Olea europaea L.) cultivation is increasingly challenged by climate change and the necessity for more sustainable crop management strategies. In this context, plant biostimulants have emerged as inputs of high potential for improving crop performance and resilience. Nonetheless, knowledge of their underlying biochemical mechanisms remains largely fragmented. Here, an untargeted GC/EI/MS-based metabolomics approach was employed to investigate the early metabolic responses of young olive trees to foliar application of two commercial biostimulants: a seaweed (SE)- and a harpin (HRP)-based formulation. Leaf samples were collected seven days post-treatment and were subjected to photosynthetic-content and metabolomics analyses. The former revealed no statistically significant differences in chlorophyll and carotenoid contents among treatments, indicating that photosynthetic pigment homeostasis was maintained. In contrast, metabolomics analysis demonstrated extensive and coordinated metabolic reprogramming induced by both products. SE treatments resulted in a primarily promoted growth-oriented metabolic profile, characterized by enhanced carbon utilization, modulation of antioxidant metabolism, activation of plastidial isoprenoid biosynthesis, and remodeling of the shikimate–phenylpropanoid pathway. Conversely, HRP treatments elicited a distinct stress-priming signature involving the accumulation of α,α-trehalose, phytol, and α-ketoglutaric acid, together with membrane lipid remodeling associated with improved osmoprotection and stress acclimation. These findings provide novel insights into the mode(s) of action of olive biostimulants and highlight the importance of metabolomics for identifying biochemical markers associated with enhanced plant resilience and sustainable olive production.