Effects Of Water And Salt Stress On Hydraulic Characteristics Of Maize Stem Xylem

Under the circumstance of global environmental change and human activity intensification,the response of plant xylem hydraulic characteristics to the stressed environment has become an important content and a hot spot in the study of plant adversity.Along with the growth of the plant stem,a number of conduits?pipe molecules or tracheids?will evolve.These conduits are an important route for the plant to carry water over long distances.They can efficiently transport water and nutrients absorbed by the root system to the leaves,ensuring a balanced water supply for the plant^[1].Therefore,to maintain the continuity of water transport in roots,stems and leaves is very important for the survival and growth of plants.In this paper,maize was taken as the research object to explore the response of maize stem xylem to different degrees of water and salt stress,so as to deeply understand the mechanism of water and salt stress inducing xylem embolization,aim at provide basic theoretical basis and data support for crops to adapt to the physiological and ecological characteristics of stress environment.To varying degrees of water salt stress of maize,set water stress?LD?,salt stress?WS?and salt water stress?SY?three stress processing,through the barrel load test in the artificial climate chamber,the low pressure fluid technology?LPFM?determination of xylem hydraulic conductance and calculate degree of embolism,study the influence of different water and salt stress on the growth physiological indexes?leaf area,plant?,gas exchange parameters?Net photosynthetic rate?Pn?,transpiration rate?Tr?,stomatal conductance?Gs?,the fluorescence parameters?,crop water potential?soil,root,leaf?and stem flow of maize.The correlation between each index and xylem hydraulic conductivity was analyzed,so as to explore the response of xylem hydraulic characteristics to water and salt stress.The main research results are as follows:?1?Water stress,salt stress and combined water and salt stress can all reduce the water potential of corn,destroy the osmotic potential balance in the plants,inhibit the photosynthetic performance of maize,cause cavitation and embolization in the stem xylem.Different stress methods had different inhibition degrees on photosynthesis of maize,and leaf photosynthesis had different influence on transpiration tension of stem xylem,among which drought stress had stronger inhibition effect on photosynthesis of maize than salinity stress.Compared with CK,the net photosynthetic rates of LD,WS and SY decreased by 49.2%,10.6%and 59.2%,stomatal conductance decreased by 74.2%,27.9%and 83.2%,and transpiration rates decreased by 65.8%,18.1%and 76.9%.The chlorophyll fluorescence parameters were all CK>LD>WS>SY trend of gradient,among them,the maximum photochemical quantum yield Fv/Fm of PS?decreased by 4.29%,5.60%,6.91%compared with CK of the control group.?2?There was a positive correlation between the effect of water and salt stress on leaf,root and soil water potential.Under the stress condition,the leaf water potential,root water potential and soil water potential of maize all decreased,which showed SY>WS>LD>CK.The leaf soil water potential difference of different stress treatments decreased with the increase of stress degree.Compared with CK of control group,the leaf soil water potential difference of each stress treatment group decreased by 12.97%,26.18%and 35.91%respectively,and the water absorption and transportation capacity of maize roots decreased significantly under stress condition.?3?Different stress methods will lead to different degrees of embolization.The higher the degree of embolization,the more serious cavitation phenomenon in the maize stem,the more difficult it is for the xylem to transport water,and the lower the flow rate of the stem.Under stress,the peak value of stem flow under LD,WS and SY treatment decreased by 54.3%,76.2%and 81.9%compared with CK,and the peak value of stem flow was brought forward by stress treatment.The higher the stress level,The more the peak value moves forward,and the daily accumulation of stem flow under each treatment was represented by CK>LD>WS>SY.?4?The initial hydraulic conductivity K_i of the stem represents the ability of the plant stem to transport water.The lower the K_i,the lower the water carrying capacity of the stem.Compared with the control group CK,the LD,WS and SY treatments have decreased by 35%,63%,71%.The hydraulic conductivity loss percentage PLC is an important parameter to quantify the degree of xylem embolism.Compared with the control group CK,the hydraulic conductivity loss percentage PLC of LD,WS,and SY treatments increased by 147%,243%,and 381%respectively.Under water and salt stress conditions,the degree of embolization of the corn stem xylem increased by about 2-4 times,and the water absorption and transport capacity of the corn decreased by 2-4 times.When the degree of embolism increased,the first phenomenon manifested in corn was wilting leaves,reducing leaf area and short plants,and plant growth was inhibited.Under the three stress treatments of LD,WS and SY,maize plant height decreased by 16.4%,25.8%,and 29.6%,and leaf area decreased by 24.7%,31.1%,and35.3%compared with CK.