Nitrate, nitrite, protein, amino acid contents, and photosynthetic and growth characteristics of tatsoi cultivated under various photon flux densities and spectral light compositions

•300 μmol m−2 s−1 PPFD is needed for appropriate tatsoi nutritional quality.•A light spectrum of 660, 640 and 445 nm is the most suitable for tatsoi cultivation.•Supplemental far-red light decreases growth and amino acid content in tatsoi.•Long-term red light is stressful for tatsoi productivity.•Light intensity has superior effect on NO3 assimilation compared to spectrum.