UV-B辐射对香蕉光合作用和不同氮源利用的影响

生长在NO3^--N、NH4^--N和NH4NO3－N的香蕉叶片有相近似的最大光合速率，UV－B辐射引起生长在不同氮源的香蕉叶片光合速率、表现量子产率和光肥利用效率的降低。UV－B辐射使生长在不同氮源的植株叶面积干重和叶氮含是降低。生长在NH4^--N的植株Vcmax和Jmax均较生长在其它氮源的高。UV－B辐射引起生长在NH4^-N的植株Vcmax和Jmax降低较相同处理的NO3^-－N和NH4NO3－N植株明显，表明生长在NH4^ －N的香蕉对UV－B辐射更加敏感。UV－B辐射改变植株的叶片的碳氢比和碳氮比。经过UV－B辐射处理的NH4^ －N生长植株的碳氮生长在NO3^--N和NH4NO3－N的低。UV－B辐射可能改变植株对不同氮源的吸收利用，从而引起碳氮代谢和酸碱调节的变化。UV－B辐射降低叶氮在Rubisco和生物力能学组分的分配系数，可能使这些组分合成减少，使叶片光调节的变化。UV－B辐射降低叶氮在Rubisco和生物力能学组分的分配系数，可能使这些组分合成减少，使叶片光合速率下降。结果表明，生长在不同氮源的香蕉植树对UV－B辐射有不同响应，NH4^ -N有利于主要光合参数增高，但其对UV－B辐射亦最为敏感。氮供应受限制或植株生长在中性盐如NH4NO3－N则对UV－B辐射不甚敏感。

INFLUENCE OF UV-B RADIATION ON PHOTOSYNTHESIS AND NITROGEN UTILIZATION OF MUSA PARADISIACA GROWN IN DIFFERENT NITROGEN SOURCES

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.