Physiological And Morphological Responses Of Ulmus Pumila Seedlings To Water Stress

Elm woodlands, a climax community which adapted to semi-arid climate and distributed on thesandland in temperate steppes, is important for withstanding the wind and protecting the ecologicalenvironment and circumjacent land resource on the sandland. However, the area of elm woodlands greatlydecreased as a consequence of serious destroying in the recent several decades. Therefore, more and moreattention has been obtained on protecting and using elm woodlands, as well as restoring its specialecological service function. This study observed the growth traits of Ulmus pumila seedling under waterstress and the recovery after water stress, and determined the responses to water stress and the adaptationstrategies of Ulmus pumila seedling. I attempted to provide some theoretical evidence for the recoveryand protecting of the elm woodlands ecological system.U.pumila seedlings were incubated in the pots and managed the water given to them after theseedlings were 30 days old in this experiment. The treatments included the light water stress (50% fieldcapacity), the medium water stress (40% field capacity), the heavy water stress (25% field capacity) and thecontrol (80% field capacity). After five weeks' treatments, all seedlings were provided water as the control.The biomass of the seedlings, leaf area, chlorophyll content, relative water content of the leaves, saturatedwater deficiency and dissociated proline content were measured.The results showed that U. pumila seedlings exhibited strong drought tolerance at the early stage ofdevelopment. Light and medium water stress influenced seedling growth without significant difference,even promoted root growth. The decrease of biomass, leaf area and chlorophyll content recovered quicklyafter the seedlings were treated the same as the control. Although, heavy water stress treatment greatlyaffected seedling growth, with 45.39% decrease of above ground biomass, 23.41% of leaf area, 28.29% ofchlorophyll content compared to control seedlings. While leaf dissociated proline content increased 68.94%compared with control seedlings, with significant difference (P < 0.05). However, below ground biomassonly decreased 14.91% and 2.67% decrease for relative water content, with insignificant difference (P >0.05).All the results showed that U. pumila seedlings exhibited strong drought tolerance at the early stageof development. Light and medium water stress influenced seedling growth without significant difference.The decrease of biomass, leaf area and chlorophyll content induced by heavy water stress couldn't recoverafter the seedlings were treated the same as the control. Therefore, the soil water content should be above5% at the early stage to insure the normal growth of U. pumila seedling, although U. pumila seedling hasstrong drought tolerance.