## 1 Introduction  
Modern crop production has to cope with increasing soil degradation and the low availability of irrigation water due to salinization, with major consequences on total and marketable crop yield as well as on the quality of the final products [1, 2, 3]. Moreover, approximately 20% of available agricultural land is affected by salinity [3], while it is expected that the current soil salinization trends will result in 50% of arable land being salt-affected by 2050 [4], mainly due to poor agricultural practices and the impact of climate change [5]. In this context, vegetable crops are highly affected by the changing conditions, especially the leafy species that are considered to be more prone to salinity than other crops [4; 5]. Therefore, cropping systems and agronomic practices have to be reconsidered in order to address the current scenario and ensure food security in the mid- and long-term, especially in the arid and semi-arid regions of the world that are most affected by salinization and irrigation water shortages [6; 7; 8]. Moreover, halophyte species, which include important bioactive compounds with health-beneficial properties, could be integrated into farming systems and contribute to food security as well as land reclamation [9; 10; 11]. Among the several cropping strategies for mitigating the adverse effects of salinity, biostimulant application is proposed as an innovative and ecofriendly tool that allows cultivation under unfavorable conditions due to abiotic and biotic stressors [12; 13; 14; 15]. Several studies have reported the beneficial effects of biostimulants on various crops grown under saline conditions. For example, [PERSON] et al. [16] recently suggested that the application of legume-derived protein hydrolyses significantly ameliorated the negative impacts of high salinity (EC levels up to 6 dS m\({}^{-1}\)) in pot-grown spinach plants. Moreover, [PERSON] et al. [17] reported similar beneficial effects on the crop performance and metabolite profile of pot-grown lettuce plants subjected to high salinity. [PERSON] et al. [18; 19] also suggested that the biostimulants obtained from seaweeds or vegetal proteins may increase tolerance to high salinity in lettuce plants through alterations in metabolic processes that induce the biosynthesis of stress-related compounds. [PERSON] et al. [20] suggested that the key mechanisms of action that are related to the beneficial effects of protein hydrolyses and plant extracts rich in amino acids as well as peptides on crops are due to osmoprotection and the scavenging of radicals at the shoot level, in addition to metal chelation and improved nutrient availability at the rhizosphere level. Irrigation with saline water may induce metabolic changes that affect the chemical composition of vegetable products, while it may also affect the visual appearance and marketability of leafy products [21]. Apart from negative effects, moderate salinity levels may improve the quality of vegetable products through the enhancement of nutraceutical compound content (e.g., phenolic compounds, carotenoids, tocopherols, vitamins, and other antioxidant compounds) or by contributing to the taste and aroma attributes [22]. Therefore, the combinatory effects of salinity and biostimulant application have to be extensively studied in order to identify those salinity thresholds and biostimulant products that allow the production of high-quality end-products without compromising marketable yield. Moreover, a thorough evaluation of germplasm variability has to be considered, since a differential response to salinity is expected depending on the genotype [23]. Successive harvesting is a common practice in various leafy greens and, according to the literature, may significantly increase the overall yield when compared to single harvesting practices [24]. Moreover, aside from increased yields this technique is cost-as well as labor-efficient and may allow for more growth cycles throughout the growing period [25].