## 3 Results and Discussion
### Evaluation of the Total Antioxidant Capacity (TAC) of Hydroalcoholic Extracts
In this case (conditions TP100), the hydroalcoholic extract showed that the highest total antioxidant capacity was obtained by cultivating the plant in the absence of PGPR, without fertilization with P\({}_{2}\)O\({}_{5}\) and K\({}_{2}\)O, and with irrigation at 40% relative soil moisture. A more detailed analysis of the results reveals that the species contributing to the antioxidant power of the hydroalcoholic extracts of _Trifolium pratense_ are primarily hydrophilic in nature, as suggested by the higher values provided by the ABTS assay compared to those of the DPPH assay, as shown in Figure 4. Supporting this hypothesis further are the values obtained from the FRAP assay, which, as mentioned earlier, particularly responds to hydrophilic species. In terms of the mechanism of action, the results for the _Trifolium pratense_ extracts seem to indicate that the species present act through both single electron transfer and hydrogen atom transfer mechanisms. It is noteworthy that in _Silbyum marianum_, all three spectrophotometric assays showed that the key parameter for optimizing the antioxidant properties of the hydroalcoholic extract is the irrigation level, indicating the presence/absence of water stress. Also, in _Achillea millefolium_ species, the results from the spectrophotometric assays consistently indicate that water stress negatively affects the quality (in terms of antioxidant power) of the hydroalcoholic extract. The findings of this study do not reveal significant effects on antioxidant capacity due to fertilizer application in two out of the three species examined. However, in the case of _Achillea millefolium_, the addition of fertilizer resulted in an increase in antioxidant capacity. This observation aligns with the existing literature, which suggests that potassium application significantly influences the phenolic composition and antioxidant capacity of medicinal plants by enhancing potassium levels in plant leaves [6]. Potassium functions as an activator for enzymes involved in both photosynthesis and the biosynthesis of starch and proteins. Furthermore, higher potassium fertilization is associated with improved plant growth [34]. The analysis carried out in the _Silbyum marianum_ assays with only PGPR showed low values of total antioxidant capacity, probably due to an induction of systemic tolerance in plants towards drought stress through a variety of mechanisms like improvement of the antioxidant system [35; 36]. A significant portion of plant damage under abiotic stress results from oxidative injury at the cellular level, caused by the production of reactive oxygen species (ROS) and their insufficient detoxification [37; 38]. To counteract this, plant cells produce various antioxidant enzymes, such as catalase (CAT), peroxides (POX), superoxide dismutase (SOD), which neutralize reactive free radicals or inhibit their formation [39]. Notably, PGPR inoculation has been shown to enhance the activity of these antioxidant enzymes under severe drought conditions, suggesting its potential use in inoculants to mitigate oxidative damage induced by drought stress [40]. Ultra High-Performance Liquid Chromatography Coupled to Mass Spectrometry (IHHPLC-MS/MS) Analysis of the Three Extracts SM101, AMI11, and TP000  
The three investigated extracts may potentially exhibit a broad spectrum of biological activities that deserve a more comprehensive investigation. Indeed, flavonoids such as apigenin, luteolin, and kaempfer are well documented for their potent antioxidant, anti-inflammatory, and anticancer properties [41], while rutin and quercetin contribute to vascular protection [42] and immune modulation [43]. Phenolic acids, including gallic and caffe acid, demonstrate antimicrobial, hepatotoxicity, and neuroprotectiveeffects [44; 45]. Chlorogenic acid and cynarin (and, more generally, dicaffeoylquinic acid derivatives) are frequently associated with hypopolipidemic and hepatoprotective activities [46; 47], notably through the enhancement of bile flow and lipid metabolism.