Selected Biochemical Properties of Medicinal Plant (Urtica dioica L.) Leaves in Relation to the Enzymatic Activity of Soils Exposed to the Impact of Road Traffic

This study examined the impact of distance from the road traffic on soil enzymatic activity, which we used as a tool to assess the relationship between soil and common nettle (<i>Urtica dioica</i> L.) used in herbalism and phytotherapy. A section of national road No. 10 (DK10) was selected for the study. Soil and common nettle leaf samples were collected from locations 5 m, 15 m, 25 m, and 100 m away from the road traffic and a control location (C). The activity of catalase (CAT), dehydrogenases (DEH), alkaline phosphatase (AlP), acid phosphatase (AcP), protease (PRO) and β-glucosidase (BG) was examined in the soil. Soil quality indices (RCh, RS, AlP/AcP, GMea, TEI) were calculated based on the enzyme activity results. The leaves of common nettles were tested for chlorophylls a and b (Chl a and b), carotenoids (Car), ascorbic acid (AAC), pH, relative water content (RWC), catalase (CATp) and superoxide dismutase (SOD) activity. Based on the values of Chl a+b, Car, pH, and RWC, the air pollution tolerance index (APTI) was calculated. The activity of the tested enzymes was statistically lowest in soil collected 5 m from traffic compared to the control (C), which was also confirmed by the results of the enzymatic soil quality indicators. In the case of CAT, AlP, AcP, and BG, based on the coefficient of determination (R2), it was found that over 70% of the variability of these enzymes was related to the distance from the road. It was found that the content of Ch a and b, Car, AAC, RWC, and pH was also lowest in soil 5 m away, whereas the activity of the antioxidant enzymes CATp and SOD was highest at this point. The ATPI values determined in common nettle leaf samples collected from locations 5 m, 15 m, 25 m, and 100 m from the road traffic were sensitive to pollution. The results indicate that the distance from the road strongly influenced the changes in the parameters studied. The enzymatic properties of the soil and selected biochemical parameters of common nettle leaves were similar at locations 15 m and 25 m, as well as 100 m and the control. The results of the enzymatic soil quality indicators show that soil 5 m from the road traffic is subject to degradation, and the nettles growing in this location are sensitive to road pollution. Therefore, it is not recommended to collect common nettle leaves from this location for medical or cosmetic purposes.