## 3 Results and Discussion
### Chlorophyll and Carotenoid Content  
Table 4 presents the result of chlorophyll and carotenoid content in relation to salinity level, biostimulant application, and harvesting time. Considering that no significant interactions between the tested factors were detected, only the main effects of each factor are presented. Chlorophylls a and b as well as total chlorophyll content was significantly affected by biostimulant application, with Trainer@showing the highest content compared to the rest of the treatments. On the other hand, salinity level affected chlorophyll b and total chlorophyll content, with increasing salinity resulting in a significant decrease, especially at the highest salinity level tested. The effect of harvesting time on chlorophyll content did not show specific trends except for chlorophyll b, where a decrease was recorded with increasing salinity, whereas chlorophyll a and total chlorophyll content fluctuated over the growing period. Moreover, total carotenoid content showed a significant increase at low salinity (EC2), followed by a reduction with increasing salinity to levels similar to the control treatment. Finally, harvesting time seems to have a varied effect, with a slight increase at the second harvest followed by a decrease at subsequent harvesting, especially the late ones (harvests V and VI), where the lowest values were recorded.  
The findings of our study are in agreement with reports in the literature, where it is suggested that salinity stress induces the disruption of the photosynthetic apparatus through the damage of chloroplasts and the decrease in chlorophyll content, especially in older leaves, which tend to accumulate more ions than younger ones [3]. Moreover, the application of biostimulants may mitigate the negative effects of abiotic stressors on chlorophyll content in leafy vegetables such as lettuce [61]. In harmony, [PERSON] et al. [16] indicated a negative effect of increasing salinity on the chlorophyll content of spinach plants, while suggesting a positive effect from the application of a biostimulant that contained protein hydrolysates. The same authors recorded an increase in total carotenoids with increasing salinity, whereas biostimulant application had no significant effect on this parameter. [PERSON] et al. [17] noted a significant decrease in SPAD index values and chlorophyll fluorescence in lettuce plants grown under saline conditions, while biostimulant application (of plant-derived protein hydrolysates) only mitigated the negative effects on chlorophyll fluorescence and not those on the SPAD index. A similar finding with our study was reported by [PERSON] et al. [27], who indicated a positive effect of biostimulants on chlorophyll b content and no effects on carotenoid content, while they also mentioned that cropping season did not affect the abovementioned parameters. The single effect of biostimulant application (borage leaf or flower extracts) did not affect chlorophyll and carotenoid content in wild rocket plants, indicating the lack of effect in unstressed plants [62]. This argument was confirmed by [PERSON] et al. [60], who suggested that borage extracts mitigated the negative effects of salinity on chlorophyll a fluorescence but had no effect on unstressed plants. It seems that growing conditions may affect the responses of plants to salinity and biostimulant application, since, according to [PERSON] et al. [52], a variable effect of protein hydrolysates and plant extracts on the chlorophyll content of perennial wall rocket leaves was recorded, depending on harvesting time.