中文摘要：

通过模拟氮沉降试验,研究了南亚热带季风常绿阔叶林林下层3种优势树种光叶山黄皮、黄果厚壳桂和厚壳桂叶片的光合生理特性对氮沉降增加的响应.试验21个月后,氮沉降显著增加了林下层3种植物叶片的全氮含量,但对磷含量没有明显的影响.总体而言,中等强度水平的氮处理（100 kg/（hm^2·a））对光叶山黄皮和厚壳桂的最大净光合速率、光饱和点以及比叶重具有明显的促进作用,表现出一定的同步性.黄果厚壳桂最大净光合速率和光饱和点则在低氮处理下（50 kg/（hm^2·a））达到最大值,而比叶重在中氮处理下达到最大值.这说明比叶重对氮沉降的敏感性远滞后于最大净光合速率.然而这些生理指标在高氮处理下普遍表现出了明显的抑制作用.氮沉降对黄果厚壳桂的光合色素有影响,其余两种植物色素随氮处理水平的变化不明显.氮处理对表观最大量子效率、光补偿点没有产生明显的影响.但光叶山黄皮和厚壳桂的表观最大量子效率表现出了低氮处理有利于植物利用光能而高氮处理不利于利用光能的变化趋势.研究结果表明,尽管季风常绿阔叶林已达到氮饱和状态,但是3种植物有一定的自我调节和适应能力.黄果厚壳桂的光合指标对氮沉降的响应比光叶山黄皮和厚壳桂敏感,在低氮条件下（50 kg/（hm^2·a））更能维持其生理优势;而其他两种植物则在中氮条件下（100 kg/（hm^2·a））生长最好.适量氮沉降在短期内还是有利于这3种植物的生长,但高氮处理（150 kg/（hm^2·a））可能已超出了植物可承受的程度,打乱了植物体内的生理进程,不利于植物的正常生长.

英文摘要：

Recent increase of nitrogen（N） deposition in forest ecosystem has shown a variety of effects on plants,including elemental imbalance,growth disturbance, foliar accumulation of free amino acids,etc.The purpose of this study is to determine the effects of simulated N deposition on the photosynthetic physiology of three dominant understorey plants（Randia canthioides,Cryptocarya concinna,and C.chinensis） in a monsoon evergreen broadleaved forest of subtropical China.The experimental design was a randomized complete block with three replications（plots） of four treatments,consisting of the control（0 kg/（hm^2·year））,low N（50 kg/（hm^2·year））,medium N（100 kg/（hm^2·year）） and high N（150 kg/（hm^2·year））.Each plot covered an area of 10 m×20 m,surrounded by a 10 m wide buffer zone.From July 2003,NH4NO3 solution,whose concentrations were about 0,0.3,0.6 and 0.9 mol/L（nitrogen） for the control,low N,medium N and high N treatments respectively,was sprayed onto the floor of these plots once every month.Here,the authors reported the results after being treated for 21 months.The foliar N content increased greatly with increasing N deposition,but there were no significant changes for foliar P content among the treatments.Generally,mediate N deposition significantly enhanced the maximum net photosynthetic rate（Pmax）,light saturation point（LSP） and specific leaf weight（SLW） for R.canthioides and C.chinensis.But the （Pmax） and LSP reached the highest values in low N treatment for C.concinna.This may imply that the responses of SLW to N deposition lagged behind the photosynthetic parameters. However,these physiologic parameters greatly and negatively responsed to high N treatment.The chlorophyll content of C.concinna increased significantly with N addition,but not significantly for the other two.The responses of apparent quantum yield（AQY） and light compensation point（LCP） for the three plants to the simulated N deposition were not significant either.But AQY of