中文摘要：

将伊乐藻幼苗种植于不同光照强度水体中,定期测定伊乐藻主要生长发育指标,并用水下饱和脉冲叶绿素荧光仪测定幼苗叶片的叶绿素光合荧光参数,研究高于光饱和点的光强、介于光饱和点与补偿点之间的光强、低于光补偿点的光强对伊乐藻幼苗生长以及光系统Ⅱ（PSⅡ）光合荧光特性的影响。结果表明：（1）不同光照强度对伊乐藻幼苗株高、叶片数、鲜重有显著影响,100%、5%、1%自然光照组伊乐藻幼苗株高、叶片数、鲜重随时间变化均呈现增加趋势,但试验后期100%自然光照组幼苗增长率有所下降,1%自然光照组增长率变缓;0.5%、0.1%、0.05%自然光照组幼苗株高、叶片数、鲜重随时间变化均呈现下降趋势,试验结束时,0.1%、0.05%自然光照组幼苗株高比初始降低了20%、60%;（2）不同光照强度对伊乐藻幼苗叶片的光合色素含量有显著影响,Chla、Chlb含量随光强减弱均呈现升高趋势,而Chla/Chlb则呈现降低趋势,表明随着光强的逐渐降低,植物通过调节色素含量来增加对光能的捕获,从而提高叶片对光能的吸收以适应外界的逆境生长环境;（3）伊乐藻幼苗光适应能力随光照强度不同而有明显差异,其中5%自然光照组幼苗光适应能力明显高于其他组,试验结束时,6组幼苗的最大电子传递速率由大到小依次为5%、100%、1%、0.5%、0.1%、0.05%自然光照组。

英文摘要：

Light is a crucial factor for growth of submerged macrophytes.Its influence on growth of Elodea nuttallii seedling was analyzed.Seedlings of Elodea nuttallii were transplanted into waters exposed to 100%,5%,1%,0.5%,0.1% and 0.05% sunlight,respectively.The sunlight intensity was controlled with a shading-net.Growth of Elodea nuttallii seedlings was investigated.Meanwhile,photosynthetic fluorescence characteristics were determined with a developed,submersible,pulse-amplitude modulated（PAM） fluorometer,or diving-PAM.Results show（1）the seedlings of Elodea nuttallii varied significantly in growth between treatments different in light density.Plant height,leaf number and fresh weight of Elodea nuttallii seedlings increased significantly with duration of exposure in Treatments 100%,5%,and 1% of sunlight.However,the growth rate of the seedlings in Treatment 100% sunlight decreased in the late phase of the experiment,and the growth rate in Treatment 1% sunlight slowed down;plant heights,leaf numbers and fresh weights in Treatments 0.5%,0.1% and 0.05% sunlight declined with duration of light exposure.At the end of the experiment,plant heights of the seedlings in Treatment 0.1% and 0.05% sunlights reduced by 20% and 60%;（2）Light intensity significantly affected chlorophyll content of seedlings.Chla and Chlb increased significantly with increasing light intensity,while Chla/Chlb ratio displayed a declining trend,which demonstrated that the seedlings attempted to catch more light energy by increasing its chlorophyll content;and（3） The photo-adaptive capacity of the seedlings varied sharply between treatments different in light intensity.It was the highest in Treatment 5% sunlight.At the end of the experiment,the 6 treatments followed the order of 5%〉100%〉1%〉0.5%〉0.1%〉0.05% in terms of the maximal electron transport rate.