In Brazilian Northeast, most of citrus orchards are submitted to seasonal water deficiency, because they are grown under rainfed condition. Grafting sweet orange trees onto drought-tolerant rootstock, such as 'Rangpur' lime, is the most used strategy to cope water deficit. However, some studies showed that adequate leaf nitrogen levels can reduce water stress symptoms in citrus. The purpose of this study was to investigate the influence of nitrogen (N) rates on proline and nitrogen leaf contents and fruit production in 4-9 years-old 'Pera' sweet orange onto three citrus rootstocks, grown without irrigation. Three simultaneous experiments were carried out with sweet orange trees grafted on 'Rangpur' lime, 'Sunki Tropical' mandarin or 'San Diego' citrandarin during five years. Aiming to that, proline, chlorophyll, and total nitrogen leaf contents, photosynthetic attributes, total tree height, canopy volume, N-use efficiency in fruit yield and productive performance were evaluated in response to N rates. After five years, effects on fruit production could be verified just in trees on 'Rangpur' and 'Sunki Tropical'. Trees on 'San Diego' presented changes in tree growth and fruit quality. In contrast, proline accumulation varied with rootstock, season, nitrogen leaf contents and N rates. The greatest content was verified in the fifth year of N rates application, particularly on the driest season. In response to N rates, 'Sunki Tropical' induced proline accumulation up to a maximum in areas with moisture availability, whereas 'Rangpur' and 'San Diego' induced increasing increases. The results indicated that proline and total N leaf contents are interdependent, closely related to N fertilization and dependent on rootstock and water availability. It is concluded that the N rates favor increases in PRO content independent to the rootstocks, 'Sunki Tropical' mandarin favors greater proline accumulation and water savings in years with longer periods of water deficit, 'Rangpur' lime, followed by 'San Diego', induces the greatest PRO contents in years with frequent short dry periods, which suggests greater resilience to changing climate, and 'San Diego' demands less N fertilizer than 'Rangpur' lime and 'Sunki Tropical' mandarin to fruit yield.
