Effects Of Water And Salt Stress On Physiological And Biochemical Characteristics And Survival Water Potential Threshold Of Four Salt-tolerant Plants At Seedling Stage

The saline-alkali soil area in China is large and widely distributed.And the coastal saline-alkali soil accounts for about 7% of the total saline-alkali land,and the area is still increasing.The improvement and utilization of coastal saline alkali land is of great strategic significance for ensuring national food security.To realize and improve the potential of saline land resources in the yellow river delta,and promote the green improvement of coastal saline alkali land,in this study,soils form the yellow river delta were selected as experimental fundamentals,and 4 salt tolerant plant including oil sunflower,cotton,alfalfa,and suaeda salsa were chose as experimental crop.We systematically investigated the response of different salt tolerant plant germination characteristics to water and salt stress,and analyzed the effects of water and salt stress on the growth status,physiological resistance,and soil water potential of different salt tolerant plants during their seedling stage.Finally,we explored the tolerance of 4 salt tolerant plant seedlings to salt alkali stress and the possibility of cultivation in different degrees of saline alkali soil.Our results could provide support for the restoration and improvement of saline alkali land,efficient development of saline alkali land resources,and optimization of planting industry structure layout.The experimental design is divided into seed germination experiment and pot experiment.The seed germination experiment was divided into 3 soil salinity gradients(2‰,4‰,and 6‰)and six soil moisture content levels(90%,80%,70%,60%,50%,and 40% of field water capacity)were set up.Each salt-tolerant plant was designed in 18 groups of experiments,three times repeated and pot experiment at seedling stage.Pot experiment was divided into 3soil salinity gradients(2‰,4‰,and 6‰)with 3 repetitions,and soil moisture was controlled at 90% field capacity.The results show that:(1)As the degree of salt and water stress increases,the emergence rate of the four salt tolerant plants significantly decreases.Under water salt coupling conditions,when the salt concentration was less than or equal to 4‰ and the moisture content was more than 40%,the seedlings of cotton,sunflowers,alfalfa,and suaeda salsa could emerge.Under the severe drought with the moisture content of 40%,the seedlings of oil sunflower and cotton could not emerge,i.e.,alfalfa and suaeda salsa have stronger adaptability to water and salt stress.The water potential of plant emergence increases with the increase of salt concentration.Among the 4 salt tolerant plants,under the same salt conditions,oil sunflower seeds have the highest germination water potential,while suaeda salsa seeds have the lowest germination water potential,indicating that suaeda salsa is the most drought tolerant and oil sunflower is the least drought tolerant.When the soil water potential is higher than-1.24 Mpa,all 4 plants could emerge.(2)Under salt stress,plant height,biomass and relative chlorophyll content(SPAD)of oil sunflower and cotton at seedling stage were inhibited.At 50 days after sowing,dry weight of cotton under 4‰ and 6‰ salt was 30.33% and 53.55% lower than that under 2‰,respectively.The dry weight of oil sunflower under 4‰ salt was 30.43% lower than that under 2‰ salt.Cotton plant height under 4‰ salinity was higher than 2‰ salinity,and low salt stress promoted cotton plant height,which reflected the cross adaptability of cotton seedlings.Salt and drought stress also promoted the decomposition of chlorophyll or inhibited the synthesis of chlorophyll.SPAD in cotton leaves was increased under low salt stress,while SPAD in oil sunflower leaves was increased under light drought.(3)There was a significant positive correlation between seed emergence rate and soil moisture,but different species had different responses to drought stress.Among the four plants,the suaeda salsa was the most drought-resistant,while the oil sunflower was the least drought-resistant.The emergence and death water potential of plants increased with the increase of soil salinity.Under the condition of soil salinity of 2‰–6‰,all the plants could survive under the condition of soil water potential higher than-1.44 Mpa.(4)With the increase of salt content,malondialdehyde content and soluble sugar content of oil sunflower,alfalfa and alfalfa were increased,and peroxidase activity and hydrogen peroxide activity were also increased significantly.Under water and salt stress,the activity of peroxidase and hydrogen peroxide increased,which maintained the stable balance of growth and development and internal metabolism of several plants.However,cotton seedlings are highly sensitive to water and salt stress in the environment.When the stress level is above medium,cotton seedlings will activate their self-defense mechanism and osmotic regulation mode to reduce the damage of water and salt stress on the seeding plants.