INFLUENCE OF UV-B RADIATION ON PHOTOSYNTHESIS AND NITROGEN UTILIZATION OF MUSA PARADISIACA GROWN IN DIFFERENT NITROGEN SOURCES
UV—B辐射对香蕉光合作用和不同氮源利用的影响

Approximately maximum photosynthetic rate was attained in leaves of Musa paradisiaca grown in NO - 3 N, NH 4 N and NH 4NO 3 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 Vc max and J max were found in plants grown with NH 4 N relative to either NO 3 N, or NH 4NO 3 N. A stronger decrease in Vc max and J max was observed in plants grown in NH 4 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. NH 4 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 NH 4NO 3 N as a major nitrogen source.