Physiological Response Of Chenopodium Quinoa Willd To Drought Stress

Severe drought has a significant impact on the sustainable development of agriculture and limits the increase of crop yields.Quinoa,with its balanced nutritional value and good stress resistance,is of considerable importance in arid land.In the experiment,two cultivars of quinoa,"Titicaca"and"Longli 1"were selected as experimental materials.Through soil weighing method,three treatment groups were designed,the control group（CK）,moderate drought stress group（MD）,and severe drought stress group（SD）.Morphological,physiological,and biochemical parameters were analyzed to investigate the physiological response of quinoa to drought stress.The key findings of this experiment were summarized below:1.Drought stress significantly reduced Fresh weight（FW）and relative growth rate of aboveground and underground for both quinoa cultivars.Following 9 d of severe drought treatment,the decrease rate of FW in aboveground and underground of Longli 1 was lower than that of Titicaca,while the increase rate of root-shoot ratio was higher than that of Titicaca.The results indicated that Longli 1 was better able to maintain growth,and had altered its nutrient allocation strategy to promote root growth to a larger extent under water deficit conditions.Furthermore,relative water content of two cultivars of quinoa showed decrease in different degree.After 9 d of severe drought treatment,relative water content of Longli 1 decreases less than that of Titicaca,showing Longli 1’s better water-holding capacity.2.Under drought stress,the photosynthesis of two quinoa cultivars,Titicaca and Longli1,were inhibited.Net photosynthetic rate of both cultivars decreased significantly,accompanied by a decrease in transpiration rate,intercellular CO₂ concentration,and stomatal conductance,indicating that the closure of stomata restricted the diffusion of CO₂ to mesophyll cells,and affected the photosynthesis of plants.Water use efficiency gradually increasing indicated that transpiration rate of quinoa was slowed down,while maintaining a certain amount of carbon assimilation,thereby achieving a"water-saving"strategy.Apparent electron transfer efficiency,actual photosystem II efficiency,and photochemical quenching coefficient of both cultivars also decreased significantly,indicating that drought inhibited the activity of the photosystem II reaction center,reducing the rate of photochemical reactions and electron transfer ability.The significant increase of non-photochemical quenching coefficient in the two cultivars indicated that more excitation energy was dissipated in the form of heat energy to protect the photosynthetic organs.In addition,drought caused a decrease in carboxylation efficiency and potential maximum net photosynthetic rate of the two cultivars,indicating that the ability of CO₂ assimilation in photosynthesis was affected.Reduction in dark respiration rate and photorespiration rate led to decrease in respiration rate and the consumption of organic matter.3.Under drought stress,the two quinoa cultivars showed different degrees of increase in the activities of antioxidant enzymes.After 9 d of severe drought treatment,Titicaca showed a greater increase in the activities of superoxide dismutase,and catalase,increasing by 25.32%and 24.79%,respectively,compared to the corresponding control.Longli 1 showed a significant increase in the activities of superoxide dismutase,catalase,and peroxidase,increasing by14.01%,27.90%and 23.64%,respectively,compared to the corresponding control.These results indicated the activities of antioxidant enzymes of two cultivars were different.In addition,drought stress increased the malondialdehyde（MDA）content contents of the two cultivars.After 9 d of severe drought treatment,MDA content of Titicaca increased by 65.00%,compared to the corresponding control,while MDA content of Longli 1 increased by 16.04%.This suggested that the damage degree of membrane lipid in Titicaca was greater than that in Longli 1.4.Under drought stress,the contents of proline and soluble sugar the two quinoa cultivars showed an increasing trend.The results indicated that the leaves-maintained turgor pressure by synthesizing related osmoregulation substances and improve water absorption capacity.After 9d of severe drought treatment,the increase in the contents proline and soluble sugar of Titicaca was greater than that in Longli 1,increasing by 136.72%and 35.66%,respectively,compared to the corresponding control.Based on the above results,this experiment used principal component analysis combined with fuzzy membership function method to evaluate the drought resistance of quinoa.The 36indicators of drought resistance were divided into four independent comprehensive indicators（cumulative contribution rate of 90.76%）,and the D value of comprehensive evaluation of drought resistance was obtained,which indicated that the drought resistance of Longli 1 was stronger than that of Titicaca.Through grey relational analysis,it was found that FW,carboxylation efficiency,net photosynthetic rate,relative growth rate,photorespiration,maximum net photosynthetic rate of light saturation,intercellular CO₂ concentration,and transpiration rate were closely related to the D value.The indexes should be used as the preferred indicators to evaluate the drought resistance of quinoa.This will provide a theoretical basis for further improving the identification indicators and evaluation methods of drought resistance of quinoa,and provide a reference for the selection and cultivation of drought-resistant germplasm resources of quinoa.