Plant growth-promoting bacteria as affected by N availability as a suitable strategy to enhance the nutritional composition of lamb's lettuce affected by global warming

•Healthier Lamb’s lettuces by the application of this novel practice.•The adequate supply of nitrogen increases the amino acids content.•A significant increase in the content of health-promoting compounds in Lamb’s lettuce with this novel practice.•A lower content of nitrates in Lamb’s lettuce after using this sustainable practice. Heat and nutritional stresses have a significantly effect on the accumulation of bioactive and other compounds harmful to human health, like nitrates, in green leafy vegetables like lamb’s lettuce. Plant growth-promoting bacteria (PGPB) have shown to confer beneficial biochemical changes to various crops under different stresses. The hypothesis proposed here is that the combination of optimal N level (2.5 Mm, 12 mM or 20 mM of N) with the inoculation of PGPB in plants exposed to heat shock (43 °C) may be a good strategy to obtain healthier lamb’s lettuce with a higher yield. Results showed that a dose of 20 mM N can be considered as overfertilization. Moreover, the inoculation of plants fed with fertilizers with reduced N and under heat stress, resulted in higher productivity and content of sugars (60 %), amino acids (94 %), nitrogen (21 %), and total phenolic compounds (30 %), and a reduced content of nitrates (27 %).