The Mitigative Effects Of Exogenous Melatonin On Quinoa(Chenopodium Quinoa Willd.)under Mixed Salt Stress

Soil salinization severely limits crop growth and development.Both neutral components and alkaline components usually coexit in the soil,causing mixed salt stress to plants.Quinoa is nutritious and has high stress tolerance,which is of great importance for the rational utilization of saline-alkali lands.Melatonin plays an important role in enhancing plant stress tolerance.In the present experiment,quinoa（Chenopodium quinoa Willd.）was used as the material.The concentration of mixed salt（Na Cl:Na HCO₃=1:1）was set at 50 m M.The physiological mechanism of different concentrations of melatonin（0,1,10 and100μM）mitigates mixed salt stress in quinoa were investigated.The main results were as follows:Exogenous melatonin improved photosynthetic assimilation capacity of quinoa by promoting the accumulation of photosynthetic pigment and regulating stomatal opening and closing.Under stress conditions,the SPAD of young leaves,functional leaves,and old leaves of quinoa increased by 17.07%,12.77%,and 14.01%,respectively when100μM melatonin was mixed applied.Exogenous melatonin increased Pn,Tr,gs,and WUE of quinoa by 1.18-fold（10μM）,64.69%（10μM）,59.49%（100μM）,and 42.77%（100μM）,respectively.In addition,exogenous melatonin alleviated the membrane lipid oxidative damage,and ensured the stability of cell structure and function.The experimental results showed that the mixed application of melatonin reduced the content of MDA content by 29.37%（10μM）.The stability of cell structure and function is necessary for the uptake,transport and redistribution of essential elements.Experimental results showed that exogenous melatonin alleviated the ionic imbalance caused by mixed salt stress.Under stress conditions,mixed application of melatonin reduced quinoa Na⁺content（root）,Cl^-content（root）and Na/K（root）by 30.23%（100μM）,28.84%（1μM）and 36.51%（1μM）,respectively.The ion contents of all parts of quinoa showed an overall increasing trend,with the contents of K⁺（leaves）,Ca²⁺（leaves）,Mg²⁺（leaves）,Fe²⁺（leaves）,B³⁺（leaves）,Mn²⁺（roots）and Cu²⁺（roots）increasing by 26.11%（100μM）,47.88%（100μM）,22.34%（100μM）,46.65%（100μM）,54.74%（100μM）,3.17-fold（1μM）,1.63-fold（1μM）.The contents of NO₃^-（roots）and SO₄^2-（leaves）increased by 1.11-fold and 42.11%,respectively.The relative stability of essential element levels further promoted a series of physiological processes,such as photosynthesis and ROS clearance,and maintained the normal physiological metabolism of quinoa.At the same time,essential elements can also acted as inorganic osmoregulatory substances in quinoa,improved the osmotic balance,and ensured more energy to be used for the growth and development of quinoa.The results showed that the mixed application of 10μM melatonin increased quinoa FW（root）,RGR（root）and R/S by45.81%,1.85-fold and 35.88%.In conclusion,exogenous melatonin increased the photosynthetic rate and water use efficiency of quinoa under mixed salt stress（50 m M）,alleviated the oxidative damage to the plant.Meanwhile,the stable contents of inorganic ions not only ensured the normal metabolism of quinoa,but also participated in the osmoregulation of the plant,which finally effectively alleviated the growth inhibition of quinoa and improved the salt-alkali tolerance of quinoa.