## 3 Results and Discussion
### Concentration of Chlorophyll A, Chlorophyll B, Chlorophyll A + B and Carotenoids in Stevia Leaves  
The concentration of various pigments (chlorophyll A, chlorophyll B, chlorophyll A + B and carotenoids) in stevia leaves varied significantly between different types of irrigation as well as the times of the stevia leaf harvest (July and September) (Figure 3). In July, all the analysed samples were characterised with a similar concentration of chlorophyll A in the range of 0.86-0.97 mg\(\cdot\)g\({}^{-1}\). In September, however, sample NR was characterised with the greater concentration of chlorophyll A (1.06 mg\(\cdot\)g\({}^{-1}\)), similar to the content in sample 0 W (0.97 mg\(\cdot\)g\({}^{-1}\)). The total concentration of this component has not increased in the samples 1 W and 2 W, in which it was even lower than in July, equal to 0.81 and 0.84 mg\(\cdot\)g\({}^{-1}\), consecutively. The concentration of chlorophyll B varied in the analysed samples in July and September. The highest concentration of chlorophyll B in July was determined for the sample NR (0.48 mg\(\cdot\)g\({}^{-1}\)), while the lowest was detected in sample 2 W (0.36 mg\(\cdot\)g\({}^{-1}\)). In September, sample NR and 0 W were characterised with a higher concentration of chlorophyll B (0.52 and 0.51 mg\(\cdot\)g\({}^{-1}\), consecutively) than samples 1 W and 2 W (0.39 and 0.40 mg\(\cdot\)g\({}^{-1}\)). The study of [PERSON] et al. [30] has shown that a crucial factor influencing the concentration of chlorophyll (chlorophyll A, chlorophyll B and chlorophyll A + B) was the year of the stevia plantation, and the amount of water used to irrigate stevia plants did not have a significant effect on its concentration. However, drought induced by the polyethylene glycol in the cultivation of stevia in the study by [PERSON] and [PERSON] [34] reduced total chlorophyll content in stevia plants almost two-fold. A study by [PERSON] et al. [37], on the other hand, has shown that chlorophyll content was almost at the same level in the stevia plants grown with adequate or deficit irrigation. Figure 3: Influence of irrigation on the concentration of chlorophyll A, chlorophyll B, chlorophyll A + B and carotenoids in leaves of stevia measured in the years 2014-2016. \(n=9\); 0 W—not irrigated, 1 W—irrigated once a week, 2 W—irrigated two times a week, NR—irrigated only during the dry periods (no rainfall). Different letters (a, b) within one parameter (concentration of chlorophyll A in July, concentration of chlorophyll A in September,...) indicate significantly different values according to Duncan’s test. The concentration of carotenoids increased from July to September only for two of the analysed samples. In July, sample NR was characterised with the greatest concentration of carotenoids equal to 2.77 mg\(\cdot\)g\({}^{-1}\), while the lowest was determined in sample 2 W (2.43 mg\(\cdot\)g\({}^{-1}\)). In September, sample 2 W was characterised with a similar, lowest, concentration of carotenoids (2.58 mg\(\cdot\)g\({}^{-1}\)), while content of carotenoids in the NR increased to 3.17 mg\(\cdot\)g\({}^{-1}\). In the before-mentioned study of [PERSON] and [PERSON] (2018), a different result was detected, because leaves of the drought-induced stevia plants were characterised with lower carotenoid content than leaves of stevia that acquired an adequate amount of water (2018). Similarly, in the study of [PERSON] et al. (2018), in leaves of stevia plants irrigated with a lower amount of water, a smaller quantity of carotenoids was found than in the control sample. However, it is important to note that these two studies were analysing stevia plants grown in warmer climate; therefore, the results might not be easily transferred to the characteristics of stevia plants grown in cooler climate in Poland.