Nitrogen Fertilizer Enhanced the Vitality of Oregano (Origanum vulgare) Plants and Boosted Their Ability to Accumulate Soil Cadmium: Agro-environmental Implications

Abstract

Soils with high cadmium (Cd) content can be decontaminated with phytoremediation. In this work, we aimed at adding nitrogen (N) fertilizer for enhancing the vitality of our test plant, oregano (Origanum vulgare). In a pristine soil, we added Cd at 0, 20, and 40 mg kg−1 soil (thereafter Cd0, Cd20, and Cd40) and two N rates at 0 and 340 kg N ha−1 (thereafter N0 and N1) in a 75-day pot experiment. We found that oregano dry weight increased significantly from 4.95 at control to 7.34 g pot−1 at Cd40N1 (a 148% increase). This indicated that the benefit of added N surpassed the negative effects of the Cd-borne stress. All other treatments had non-significant differences compared to the control. Cadmium content in oregano aerial biomass was zero in the unamended treatments, raised to 0.35 mg kg−1 at Cd40N0, and to 1.11 mg kg−1 at Cd40N1. Further, we assessed the plant’s performance in regard to its potential use as a phytoremediation species. We calculated the Cd soil-to-plant transfer coefficient (TC; maximum was 0.042) and the root-to-shoot translocation factor (TF; maximum 0.171). Both indices exhibited the failure of oregano as a potential hyperaccumulator. However, our findings rather confirmed our scientific hypotheses that N addition to soil boosted plant’s ability to accumulate Cd (as indicated in the significant twofold increase in shoot content of Cd and the 7.8-fold increase in TF at Cd40N1 compared to Cd40N0). We conclude that boosted vigor by added N is a promising method for enhancing phytoremediation of Cd-contaminated soils, but further field tests are necessary regarding oregano to verify those findings.