Abstract:Approximately maximum photosynthetic rate was attained in leaves of Musa paradisiaca grown in NO3--N, NH4+-N and NH4NO3-N. UV-B radiation induced decreases of photosynthetic rate, apparent quantum yield and efficiency of energy conversion in plants grown with all three nitrogen sources, but to different degrees. Exposure to UV-B radiation resulted in lower levels of leaf dry mass per area and leaf nitrogen content per unit leaf dry mass and a slightly elevated level of chlorophyll content. Higher levels of Vcmax and J max were found in plants grown with NH4+-N relative to either NO3-N, or NH4NO3-N. A stronger decrease in Vcmax and Jmax was observed in plants grown in NH4+-N with exposure to UV-B radiation, indicating a greater sensitivity to UV-B radiation. UV-B radiation induced a change in the carbon: hydrogen and carbon: nitrogen ratios and may induce a change in nitrogen utilization, carbon and nitrogen metabolism and acid-base regulation. Decreases in the partitioning coefficient for leaf nitrogen in Rubisco and in bioenergetics were found with increasing exposure to UV-B radiation which may cause a decrease in the synthesis of these compositions and in photosynthetic rate. The results show that plants grown in different nitrogen-sources had the ability to vary their responses to UV-B radiation. NH4+-N supply may act to increase relative photosynthetic parameters and may be capable of being subjected to more severe UV-B radiation impact. Lower sensitivity to UV-B radiation may occur for nitrogen limited plants or those with NH4NO3-N as a major nitrogen-source.