## 3 Results and Discussion
### Chemical Composition of Plants
#### 3.2.2 Micronutrient Content  
Micronutrients, namely nutrients that are needed by the body in very small amounts (below 0.01% of body weight), include chromium, cobalt, copper, manganese, and zinc, and they occur at very low concentrations in the natural environment. Large quantities of these metals can be toxic to humans [43]. Vegetables of the family _Brassicaceae_ are abundant in micronutrients, which enhances their nutritional value. The mineral composition of plants is influenced by fertilization and the applied substrate [44]. The micronutrient content of leaves in the studied _Brassica_ species is presented in Table 4 and Figure 5. The content of iron, zinc, and boron was linked with plant species, whereas manganese content was associated with the substrate. Copper levels in leaves were influenced by both substrate and plant species. The content of all micronutrients was affected by the interaction effects of substrate and plant species. The content of iron in _Brassica_ leaves grown on the tested substrates ranged from 51.0 mg kg\({}^{-1}\) DM (cauilflowers grown on the control substrate) to 144.9 mg kg\({}^{-1}\) DM (white cabbage grown on PRO1). In comparison with the control treatment, substrates used in the experiment increased the iron content of leaves in cauliflowers by around 13% (PRO1) to around 72% (PRO3), and decreased the iron content of leaves in broccoli by around 22% (PRO2) to around 38% (PRO3). In white cabbage, the iron content of leaves increased by around 37% on PRO1, and decreased by around 35% and 49% on PRO2 and PRO3, respectively. The tested substrates exerted different effects on manganese concentration in the leaves of the analyzed _Brassica_ species. The above parameter ranged from 13.6 mg kg  
Figure 5: The influence of the tested substrates on the micronutrient content of leaves in seedlings of the analyzed _Brassica_ species: a–k–various letters denote significant differences at \(p<0.05\) (Tukey’s test). DM (white cabbage grown on PRO3) to 52.4 mg kg\({}^{-1}\) DM (broccoli grown on PRO1). In comparison with the control treatment, substrate PRO1 increased leaf manganese levels by around 15% (white cabbage) to around 30% (cauliflowers). In plants grown on PRO2, the manganese content of broccoli leaves was similar to that noted in the control treatment, lower in white cabbage leaves (by approx. 47%) and higher in cauliflower leaves (by approx. 30%). In turn, substrate PRO3 decreased the above parameter in broccoli (by approx. 26%) and white cabbage (by approx. 69%), but increased the manganese content of cauliflower leaves (by approx. 50%) relative to the respective controls. The zinc content of leaves in the studied _Brassica_ plants ranged from 24.8 mg kg\({}^{-1}\) DM (cauliflowers grown on PRO3) to 76.0 mg kg\({}^{-1}\) DM (broccoli grown on the control substrate). In broccoli, alternative substrates induced a considerable decrease in the zinc content of leaves, from around 36% (PRO1) to around 60% (PRO3). White cabbage grown on PRO2 and PRO3 was characterized by considerably higher zinc levels (by approx. 46% and 38%, respectively), compared with the control treatment. In cauliflowers, leaf zinc levels were significantly lower on PRO1 and PRO3 (by approx. 8% and 25%, respectively) than in the control treatment. The boron content of _Brassica_ leaves ranged from 10.6 mg kg\({}^{-1}\) DM (cauliflowers grown on PRO3) to 22.0 mg kg\({}^{-1}\) DM (white cabbage grown on PRO1). In broccoli, substrates used in the experiment increased boron concentration by around 6% (PRO3) to around 28% (PRO1 and PRO2) relative to the control treatment. Alternative substrates exerted varied effects on the boron content of white cabbage leaves. In comparison with the control substrate, the analyzed parameter decreased by around 7% and 23% in PRO2 and PRO3, respectively, and increased by around 20% in PRO1. Substrate type had the least differentiating effect on the boron content of cauliflower leaves.