Growth And Physiological Responses Of Ulmus Macrocarpa Hance To Different Water Stress At Seedling Stage

In this paper,we used Ulmus macrocarpa Hance as the experimental material to study the effects of water stress on the morphological structure,leaf water physiology,biomass,photosynthetic system,chlorophyll content,osmotic adjustment substances,and membrane lipid peroxidation products of 1 year old Ulmus macrocarpa Hance.To explore the response and adaptability of Ulmus macrocarpa Hance under different water stress conditions,understand the drought resistance mechanism of Ulmus macrocarpa Hance,provide theoretical basis for the introduction and cultivation of Ulmus macrocarpa Hance in arid regions.The main research results obtained are as follows:1.With the deepening of water stress degree,the net photosynthetic rate,transpiration rate and stomatal conductance of Ulmus macrocarpa Hance decreased to varying degrees,but the trend of intercellular CO₂ concentration was not consistent,and by improving the light compensation point,reducing light saturation point,apparent quantum efficiency,and dark respiration rate to deal with the reduction of soil moisture.With the increase of photosynthetically active radiation intensity,the values of water use efficiency from high to low were moderate drought stress>mild drought stress>suitable moisture>severe drought stress.2.Under different water treatments,there was a significant difference between the high growth rate of seedlings and the increase in ground diameter,both of which decreased with the decrease of soil moisture in the soil ponds.The water conditions suitable for seedling height and ground diameter were suitable moisture>mild drought stress>moderate drought stress>severe drought stress.3.With the intensification of water stress and the prolongation of time,the leaf water content and relative water content of the Ulmus macrocarpa Hance showed a downward trend,while the water saturation loss had a significant increase.The water retention capacity of leaves under severe drought stress was greater than other treatments during each time period.4.The total chlorophyll content,chlorophyll a and chlorophyll b content decreased with the decrease of soil water content.Among them,the change of chlorophyll b was smaller than that of chlorophyll a,and the decrease of chlorophyll a content is the main reason for the decrease of total chlorophyll content.The ratio of chlorophyll a/b under suitable water,light and moderate drought stress did not fluctuate significantly during stress time,on the 28th day after water stress,the ratio of chlorophyll a/b was significantly lower than that after 21d.5.Under water stress,the total biomass and aboveground biomass of Ulmus macrocarpa Hance showed a downward trend.However,the biomass of the underground part of Ulmus macrocarpa Hance increased with the increase of the water stress,and the water stress had a stronger effect on the aerial part of the Ulmus macrocarpa Hance.Under drought stress,the ratio of root to crown of Ulmus macrocarpa Hance increased significantly,and the ratio of root to shoot reached the highest value under severe drought stress.6.With the decrease of soil moisture content,the soluble sugar content and MDA content of Ulmus macrocarpa Hance increased to varying degrees.With the prolongation of stress time,the soluble sugar content of Ulmus macrocarpa Hance fluctuates little under suitable water and mild drought stress,but it rises first and then decreases after moderate and severe drought stress.During the whole water stress test,the content of MDA under severe drought stress was significantly higher than that of suitable moisture treatment.