Abstract: According to the different soil water contents,the light response of photosynthesis of potted three ecotypes of reeds(fresh water swamp reeds,FWSR,salt meadow reeds,SMR,and salty water swamp reeds,SWAR) collected from the reed wetland in Yellow River Delta are measured,and their moderate soil water content ranges during the fast growing period are compared,so as to provide the evidence for the establishment of the ecological water requirement standards in reed wetland.The results show that the maximum net photosynthesis rate of FWSR,when the soil relative water content is 95.6%,is signifi-cantly higher than that in the waterlogged condition(p< 0.05).However,for SMR and SWAR this difference is not signifi-cant(p> 0.05).The net photosynthetic rates of the three ecotypes of reeds have different response thresholds to the alteration of soil water content.And the tolerance of FWSR to soil water stress is stronger than the other two ecotypes,which may be mainly due to the different soil salinities in their habitats.