*2.1. Screening of Pepper Cultivars with Different Low-N Tolerance*

The low-N tolerance of 100 pepper cultivars was analyzed hydroponically in a greenhouse at the Chongqing Key Laboratory of Adversity Agriculture. Yamazaki nutrient solution for pepper was used as a sufficient-N solution containing 1.50 mM Ca(NO3)2·4H2O, 6.00 mM KNO3, 0.83 mM NH4H2PO4, 0.75 mM MgSO4·7H2O, 0.10 mM FeSO4·7H2O, 0.10 mM Na2EDTA, 0.05 mM H3BO3, 0.0008 mM ZnSO4·7H2O, 0.01 mM MnSO4·4H2O, 0.0003 mM CuSO4·5H2O, and 0.00002 mM (NH4)6Mo7O24·4H2O. Pepper seeds were soaked in warm water (55 ◦C) for 30 min, and then germinated in the dark on moist filter papers at 25–28 ◦C. Small buds were then transferred to foam boards floating in

black plastic boxes filled with distilled water. The foam boards consisted of 15 uniform holes in which 15 plants grew. After seven days, the distilled water was changed to onehalf-strength sufficient-N solution. A week later, the solution of half of the seedlings was changed to low-N solution, in which the concentrations of Ca(NO3)2·4H2O, KNO3, and NH4H2PO4 were 20% that of the sufficient-N solution, and the other nutrients were the same as the sufficient-N solution. Furthermore, K2SO4, KH2PO4, and CaCl2 were added in moderation to the low-N solution to avoid K, P, and Ca deficiency. The rest of the seedlings grew under N-sufficient condition as controls. Each cultivar had three replicates (15 plants/replicate) for each N condition (sufficient-N or low-N). The culture solution was refreshed every seven days at pH 6.2–6.4. All plants were grown in a greenhouse at 28 ◦C (day) and 25 ◦C (night) with a relative humidity of 70–80% and a photoperiod of 14/10 h, 300 μmol m−<sup>2</sup> s<sup>−</sup>1. The leaf areas, shoot dry weights, root dry weights, and plant dry weights were evaluated 28 days later.
