Functional Trait-Based Responses of the Moroccan Menara Cultivar to Deficit Irrigation

The olive tree ( Olea europaea L.) is a keystone species in Mediterranean agroecosystems, where it plays a central economic and cultural role. However, the Mediterranean Basin is increasingly exposed to climate change, with rising temperatures and prolonged droughts threatening the long-term sustainability of olive cultivation. Understanding the adaptive responses of olive trees to water scarcity is critical for ensuring resilience in olive-based agroecosystems. This study investigates the functional responses of the Moroccan Menara olive cultivar under different controlled deficit irrigation (DI) strategies, namely regulated (RDI) and sustained (SDI) deficit irrigation. By analyzing key leaf functional and biochemical traits, we assessed how varying levels of water stress influence resource allocation and stress mitigation mechanisms. Under full irrigation (100% of crop water evapotranspiration) throughout the growing season and during sensitive growth periods, trees exhibited increased stomatal density, leaf area, and higher leaf carbon, nitrogen, and phosphorus contents, traits associated with enhanced growth and photosynthetic capacity. Meanwhile, under RDI treatments, with a 20% water reduction during sensitive periods and 40% during non-sensitive periods, Menara trees showed increased leaf tissue density and accumulation of polyphenols. SDI treatments, however, triggered higher concentrations of osmoprotectants (glycine, sugars, and proline), reduced stomatal density, and smaller leaf area associated with increased stomatal size. Principal component analysis revealed a major trade-off between growth-related and stress-protective traits, primarily driven by water availability during phenological growth stages. Notably, the strength of this trade-off was positively associated with olive fruit yield, underscoring the importance of strategically timed irrigation in balancing physiological resilience and productivity. These findings emphasize the crucial role of irrigation strategy in modulating functional responses of olive trees to water deficit, offering insights into optimizing water use under future climate scenarios.