Abstract

In three consecutive years of field experiments, an uncovered control (T₀), and floating row covers treatment (T₁: perforated polyethylene, 50 μm; T₂: polypropylene, 17 g m^–2) were used to produce different growth conditions for Chinese cabbage [Brassica pekinensis (Lour) Rupr. cv. Nagaoka 50]. Five samplings (whole tops) were made between transplant and harvest, and measurements were made of NO₃^-, NH₄⁺. organic N, and Mo concentrations, as well as nitrate reductase (NR) activity, and amino acids in the whole shoots. The microclimatic conditions in T₀ resulted in plants with higher Mo accumulation, as well as the highest basal NR activity and the lowest NO₃^- concentrations. The thermal environment under the T₁ treatment induced the highest mean temperature values and resulted in plants with the highest amino acid level, whereas the plants in the T₂ treatment with its intermediate thermal conditions, had the lowest levels of Mo and the highest NO₃^- concentrations. The floating row covers influenced the Mo status, which in turn affected NR activity. In addition, T₁-polyethylene sheet and T₂fleece favoured an increase in the levels of NO₃^- by the limitation in the NR activity, with the consequent risk of a high NO ₃^- level in vegetables for human consumption.