The findings of the study suggest that the δ(15)N value of lettuce tissues could be used as a rough marker to reveal the history of nitrogen fertilisation, but only in the case of single fertiliser application. However, if the difference in δ(15)N between the applied synthetic and organic nitrogen fertilisers was > 9.1 ‰, the detection of split and combined usage of the fertilisers would have greater discriminatory power.

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The interactions between the uptake of selenium (as selenite and selenate) and iodine (as iodate and iodide) by red chicory (Cichorium intybus L. var. foliosum Hegi) and their effects on selected morphological and physiological characteristics were investigated. Seedlings were transplanted to the field, and at the onset of head formation, the plants were foliar-sprayed with the following solutions: Milli-Q water (control), Se (IV), Se (VI), I (−I), I (V), Se (IV) + I (−I), Se (IV) + I (V), Se (VI) + I (−I) and Se (VI) + I (V). The different treatments had no significant effects on the yield (39.8–51.5 t ha−1) and mass (970–1200 g) of the chicory heads. The selenium content in Se-treated plants was up to 5.5-times greater than the control plants. The iodine content in the chicory leaves enriched with I was 3.5-times greater than the control plants. Iodide or iodate, applied together with selenite in the spray solution, increased the uptake of Se by chicory plants, while both forms of iodine, applied together with selenate, reduced the uptake of Se. Plants treated with I (V) had lower amounts of chlorophyll a and carotenoids than the control, while respiratory potential was higher than the control, which indicated the possible presence of stress in I (V)-treated plants. However, the potential photochemical efficiency of photosystem II was similar and close to the theoretical maximum (0.83) in the control and treated groups, which indicated that all of the plants were in good condition. Furthermore, the plant mass and yield were comparable in the control and treated groups. Molecular studies, like gene expression analysis, would represent a major upgrade of the present study by defining the mechanisms of Se and I uptake and their interactions and by enhancing the knowledge of the Se and I transporters.