Since the Industrial Revolution, the CO2 concentration in the atmosphere has increased from 280 ppm to more than 400 ppm today. Elevated atmospheric CO2 (eCO2) can lead to increased biomass for many C3 species (the so-called ‘CO2 fertilization’ effect). However, an unexpected outcome is that increases in biomass under eCO2 is associated with a lower plant nutritional quality. The reasons and mechanisms underlying the negative impact of eCO2 on the mineral nutrition of C3 plants are still unclear. One hypothesis is that eCO2 could lead to a decrease in the efficiency of mineral acquisition by plant roots. Compared to the huge amount of data on the responses of the shoots to eCO2, only a fragmentary knowledge is available about how eCO2 affects root physiological and developmental processes, and even less under nitrate (NO3-) starvation. Our project aims to address two hypothesis to explain the plant mineral status (especially nitrogen N) decline under eCO2. Our main results showed that: i) Increase in shoot biomass in response to eCO2 is independent of NO3- condition but leads to a huge decrease in N levels in plants grown on 0,5 mM NO3- ii) Gene of NO3- absorption and assimilation enzymes are affected by eCO2 especially under very low NO3- condition suggesting an important role of eCO2 on the high affinity transport system iii) The root system architecture is stimulated in response to eCO2 with an increase in primary root growth and a lateral root density in low NO3- condition. these results suggest that eCO2 promoted root morphological development and expansion, implying that the sensitive responses of root morphology and function to eCO2 would increase long-term belowground C sequestration but cannot be an explanation for the reduced efficiency of root nutrient uptake.