中文摘要：

采用上下分根方法及根系观测技术,设置控制处理（仅接受白天自然光照）,夜间光照处理（接受24 h光照）,加水及夜间光照处理（接受24 h光照＋加水）,对梭梭根系是否存在水分再分配作用进行了验证,在此基础之上,进一步研究了水分再分配对梭梭生理和形态的影响。结果表明：（1）控制处理梭梭黎明前及正午同化枝水势高于夜间光照处理,且控制处理和加水及夜间光照处理梭梭上管部分根水势也较夜间光照处理高,说明夜间弱蒸腾作用下,控制处理的梭梭发生了水分再分配作用。（2）水分再分配作用促进梭梭蒸腾及光合作用,控制处理与加水及夜间光照处理的梭梭蒸腾速率均大于夜间光照处理,且控制处理和加水及夜间光照处理的梭梭最大净光合速率也较夜间光照处理高。（3）控制处理与加水及夜间光照处理梭梭地上部分生物量显著高于夜间光照处理,不同处理的梭梭地下部分总生物量、上管地下部分生物量及上管比根长的关系为：加水及夜间光照处理〉控制处理〉夜间光照处理。梭梭具有水分再分配作用,在夜间弱蒸腾条件下,根系吸收下层湿润土壤中的水分并释放至上层干燥土壤中,以缓解干旱环境下植物的水分亏缺,水分再分配作用可促进植物蒸腾及光合作用,增加植物的根冠比和根系碳分配。

英文摘要：

Water redistribution within split-root pot cultivation experiment was root system can mitigate root drought conducted to test the effects of root stress in dry season. In this study, a hydraulic redistribution of Haloxylon ammodendron, and the root dynamics was observed by minirhizotron method. Considering the occurrence of hydrau- lic redistribution in the low evaporative demand, a series of growth and water physiological and root dynamic charac- teristics of plant in wet and dry split rhizospheres of pot were measured under three treatments ： control （C） ： 24- hour light ＋ supplemental water （LW） ; and 24-hour light only （L）. The results are as follows ： （1） The leaf water potential of plant in control at dawn and on midday was higher in compared to that in light treatment, and the root water potential of dry soil zone （the upper tube） in control and light and water addition treatment was also higher than that in light treatment. This result indicated that water potential of roots in dry soil zone in control partly recov- ered at dawn on next day due to the hydraulic redistribution at night; （2） The transpiration and the maximum net photosynthetic rates under the control and light and water addition treatments were higher than those in hght treat- ment, which suggested that the root internal hydraulic redistribution protected the deterioration of plant photosynthet- ic physiological activities under draught stress; （3） The aboveground biomass under light treatment was lower in compared to that in the control and light and water addition treatments, and the root dry weight of the whole plant, root dry weight in dry soil zone and specific root length （SRL） were significantly different among the treatments and in a rank of LW 〉 C 〉 L. in sum, the effects of water hydraulic redistribution on water potential and photosynthetic characteristics of H. ammodendron were observed, which proved that the hydraulic redistribution could protect the roots of desert shrub in topsoil u