RESUMONeste estudo foram avaliados os efeitos do nitrato (NO 3 -), amônio (NH 4 + ) e da ausência de nitrogênio (N) na fotossíntese, no processo fotorrespiratório e no metabolismo antioxidante de plantas jovens de seringueira. As plantas foram cultivadas em areia, irrigadas com solução nutritiva de Bolle-Jones, com N na concentração de 8mM nas proporções + proportions: 8/0, 0/8 and 0/0, respectively. The gas exchange, chlorophyll a fluorescence, photorespiration and antioxidant enzyme activities (SOD, CAT and APX) in leaves were evaluated. The net CO 2 assimilation rate (A) and the electron transport rate (ETR) were higher in NO 3 -treated plants. Lowest ETR and higher photorespiratory activity were observed in plants treated with NH 4 + . SOD activity was higher in leaves of plants treated with both N sources. Lower CAT and higher APX activities were found in NO 3 -treated plants. Plants grown in the absence of N showed lowest values of A. We observed that the different N sources significantly affected the photosynthetic process and that NH 4 + favored photorespiratory process in rubber plants.