## 4 Discussion  
### Plant and Enzyme Response to Petrochemical Products  
The effectiveness of phytoremediation processes in soils contaminated with petroleum products depends on the selection of appropriate plants [86; 87; 88; 89]. These should be fast-growing plants with high adaptability to challenging environmental conditions and a well-developed root system [88; 90]. Examples of such plants include _Sorghum bicolor_[86], _Iris lacteal_[91], _Festuca arundinacea_[92; 93], and _Lathyrus sativus_[94]. Plants obtained from degraded areas can be used for energy purposes, as their combustion heat and energy values remain unchanged [74; 95]. In our own research, _Zea mays_ was utilized, which meets all the aforementioned criteria. This is evidenced by the biomass yield of _Zea mays_ obtained in the experiment, which ranged from 69,544 to 74,073 g pot\({}^{-1}\) in uncontaminated objects. Comparing the two environments contaminated with petroleum products, we found that _Zea mays_ adapted better in the G-contaminated soil than in the DO-contaminated soil. The influence of pollutants on plants depends on the chemical composition of petroleum products [96; 97] as well as on soil properties [98; 99]. Particularly long-lasting effects occur in soils characterized by low organic carbon content and low biological activity, as the biodegradation rate of hydrocarbons is slow under such conditions [36]. In our study, the negative effect of diesel oil (DO) applied to the soil at a rate of 16 cm\({}^{3}\) kg\({}^{-1}\) on _Zea mays_ biomass was almost twice as strong as that of gasoline (G). This was probably due to greater adsorption of oil residues on the soil mineral surfaces, resulting in a change in the redox potential of the soil [100]. Soil colloids covered with hydrophobic films lose their water-holding capacity and decrease their conductivity [16; 24]. As a result, the upper parts of the contaminated soil dry out, while the lower parts become excessively moist, leading to the predominance of anaerobic processes [98]. The negative impact of petroleum products on the environment depends on the density of the product [101]. According to [PERSON] [99], the effect of heavy oil fractions on plants is long-lasting compared to light fractions, which are more rapidly decomposed by microorganisms and rapidly migrate out of the soil. This observation agrees well with our results, since the density of diesel oil, which destabilized plant growth and development more, ranged from 0.820 to 0.845 g cm\({}^{-3}\), while that of unleaded gasoline ranged from 0.720 to 0.775 g cm\({}^{-3}\). According to [PERSON] [102], the negative effect of petroleum products results not only from their direct effect on the root system and the reduction of soil oxygen content but also from the decreased availability of nutrients for plants. An important factor limiting nutrient availability to plants is the increase in organic carbon content, leading to an increase in the C:N ratio [92; 98; 103]. Similarly, in our own study, a significant increase in soil organic carbon content and consequently an expansion of the C:N ratio were observed in soil contaminated with diesel oil (DO). There was also a significant increase in soil pH and sorption capacity. In contrast, the effect of gasoline on these parameters was minimal. These changes are consistent with our earlier studies [21; 104]. The destabilization of water-air conditions under the influence of petroleum-derived products and changes in soil properties, such as pH value, C\({}_{\text{org}}\) content, total nitrogen (N\({}_{\text{total}}\)), and sorption capacity, indirectly affect not only the plant growth but also the activity of soil enzymes, which are considered reliable indicators of soil health and accurately reflect the ecological state of the soil [34]. According to [PERSON] et al. [105], the implementation of any soil remediation strategy should be preceded by the determination of enzyme activity since they are the driving force behind biochemical transformations.