Effects Of Water-Retaing Agent On Survival Rate And Physiological Indexes Of Tree Seedlings During Water Stress

This paper deals with three textures of soils such as sandy soil, lightloam soil and loam soil with five different levels of water-retaining agent, effects oftreatment on soil water content and physiologic indexes of one-year-old Robiniapseudoacia L .and platy clad us orientals seedlings. The results showed that:Under natural condition with open air , the water absorbing capacity and water retaining properties of water-retaining agent were quite well, multi-comparision showed that at the levels of 1 kg.m"3 and 2 kg.m'3 the water content of light loam soil and loam soil were significantly higher in the process of drying than that of the control, but the 1 kg.m"3 level of sandy soil had no significant difference with control.The more quantity of water-retaining agent was used in the soil .the higher the seedling survival rate .The survival rate of 2 kg.m"3 level of two kinds of seedlings can be increased 60% than that of the control.Different levels of water-retaining agent could differently release the bad influences in seedlings under the condition of water stress .Water-retaining agent could alleviate the stress of drought on seedlings .With the dry intensity became higher and higher the net photosynthesis became lower. 1 test and Q test showed that to sandy soil only the dosage was not less 1 kg.m"3, can the water-retaining agent had clearly effects on net photosynthesis dropping. While to light loam soil and loam soil, 0.5kg.m"3 level can effectively prevent the dropping .During water stress, Robinia pseudoacia L . chlorophyll a fluorescence parameter (Fv/Fm, PS II ,qp ,NPQ )decrease gradually. The more quantity of water-retaining39agent was used in soils (light loam soil and loam soil), the less Robinia pseudoacia L . chlorophyll a fluorescence parameter dropped .When water-retaining agent level reached to 0.5 kg.m"3 ,the dropping could be effectively prevented.