## 4 Discussion
### Yield, Quality, Antioxidants, and Mineral Composition
The interaction between cultivar and biostimulant formulation was significant on nitrogen use efficiency (NUE) and, indeed, four of the five varieties tested (Mars, Naples, Tricia, and Olivetta) showed significant enhancements in NUE upon protein hydrolysate application, compared to the untreated control (+22.6%, +28.0%, +26.8%, and +22.8%, respectively). The latter increases highlight the potential of legume-derived protein hydrolysates to improve nitrogen utilization in wild rocket, consistent with previous reports [24] about the biostimulant encouragement of nitrogen metabolism and nutrient use efficiency in maize seedlings through modulation of enzyme activities. The mentioned positive effects of biostimulants are likely connected with their rich array of peptides and amino acids, which can encourage nitrogen metabolism, also fostering nitrate reductase activity, as reported by [PERSON] et al. [42]; the latter authors found that protein hydrolysate application under suboptimal N fertilization regimes boosted the marketable yield of greenhouse spinach through the enhancement of nutrient uptake and photosynthetic efficiency. The cultivar Venice showed a different response pattern, with only _Spirulina platensis_ treatment leading to higher NUE (+33.3%), compared to the control. Similarly, [PERSON] et al. [19] observed that _Spirulina_ applications altered nitrogen assimilation patterns in lettuce, resulting in enhanced nitrogen use efficiency, while maintaining or reducing tissue nitrate concentrations. The different NUE responses of wild rocket cultivars to biostimulants recorded in our research are consistent with previous reports [43] regarding yield increases in different leafy green genotypes, from 11% in Swiss chard to 36% in mustard greens under seaweed extract application. Similarly, [PERSON] et al. [44] observed significant interactions between durum wheat varieties and biostimulant formulation on production and resource use efficiency. The highest performance of protein hydrolysate in improving NUE in different cultivars, connected with its rich amino acid and bioactive peptide profile, has also been reported by [PERSON] et al. [45] in terms of enhancement of nitrogen uptake and assimilation in tomato plants, with genotype-dependent response magnitude. The latter authors attributed the mentioned effects to the ability of protein hydrolysates to modulate root architecture and encourage the activity of key enzymes involved in nitrogen assimilation. Other authors reported variety-dependent reactions to biostimulants in baby rocket [39], the increase of photosynthetic efficiency and, accordingly, of carbon skeleton availability necessary for nitrate assimilation in spinach [21], and the modification of root architecture and functions in _Corchorus olivorius_, potentially altering nitrogen uptake patterns and improving NUE [46]. Consistent with our findings, [PERSON] et al. [7] emphasized that genotype is a primary determinant of nitrate accumulation in leafy vegetables, along with environmental and management factors, including biostimulant application serving as modulators of genetic predisposition. In the present study, the different reactions of the cultivar Venice to _Spirulina_ application, compared to the other cultivars, agrees with the reports of [PERSON] et al. [47], who demonstrated that the enhancement of antioxidant levels and metabolic processes, elicited by seaweed extracts in spinach, varied with the genotype. All the biostimulant treatments elicited the peak of malate accumulation in autumn-winter, with the protein hydrolysate and _Spirulina platensis_ showing a better effect than the untreated control in the mentioned crop cycle. The latter biostimulant-induced amplification of malate synthesis suggests the modulation of carbon metabolism enzymes, consistent with the reports about the effect of protein hydrolysates in increasing the activity of TCA cycle enzymes [22]; in contrast, citrate showed the highest levels in the autumn crop cycle under all the treatments.