## 4 Discussion
This study's monoterpene emissions from the NSAIDs tested showed no significant differences. This finding implies that the pathway flux into monoterpene synthesis was independent of NSAID type after induced monoterpene emission. The emission of green leaf volatiles (C5 and C6 aldehydes and ketones) is mainly due to biotic or abiotic stress factors acting on plants. Indeed, the emission of different green leaf volatiles has been found for plants under drought, temperature [61], flooding, or herbivores [62]. The plants treated with paracetamol have been shown to have the highestemission of 1-hexanol, followed by diclofenac stressed plants. The findings of this study provide more evidence that green leaf volatiles emissions are a highly sensitive predictors of how plants react to NSAIDs. The flavonoid concentration in leaves decreases for all plants treated with NSAIDs. The same results have been reported for the treatment of wheat with a high concentration antibiotics solution [63]. During times of oxidative stress brought on by variables in the surrounding environment, one of the roles of flavonoids is to lessen the impact of reactive oxygen species [64]. Such behavior demonstrates that a persistent effect of drugs can impair the antioxidative capacity of the foliage, which indicates that the foliage's ability to defend itself gets depleted [65]. Important plant constituents with redox characteristics and antioxidant action are phenolic compounds. Their concentrations in leaves usually increase during short-time oxidative stress (see [66] for review), but in the case of prolonged stress, the total concentration of phenolic compounds could decrease [67]. In our experiment, the concentration of total phenolic compounds decreased for plants under stress conditions for some species. In contrast, for others (such as _Vicia faba_), the phenolic compounds were disturbed only in plants treated with naproxen. Such a decrease in the antioxidant capacity has been found in _Atriplex patula_ L. plants treated with naproxen [43]. Such behavior is correlated with reducing the content of carotenoids and flavonoids. From the principal component analysis (PCA) plot with only photosynthetic parameters and photosynthetic pigments (Figure 10, Data in Supplementary Table S1), the _Cicer arietinum_ plants were the most influenced by the presence of NSAIDs, while the _Pisum sativum_ plants were less disturbed. It has already been shown that chickpea plants are sensitive to soil salinity [68] and temperature [69], and the present study demonstrates, once again, its sensitivity to abiotic stresses. From the PCA plot with all available data (Figure 11), the clustering of control plants could be seen compared with the treated plants. Even more, the _Pisum sativum_ plants express high sensitivity to NSAIDs, but there is no clear pattern for the other species. Figure 10: The principal component analysis plot (PCA) with photosynthetic parameters and pigments of plants in 0.5 L pots filled with commercial garden soil that were treated by watering 100 mL of 0.5 mg L\({}^{-1}\) NSAIDs every second day over a total of 20 days. PCA 1 and 2 explain 84.5% of the variation (61.9% and 22.6%, respectively). See Supplementary raw data in Table S1.