Physiological Mechanisms Of Improving Germination And Seedling Growth By Manganese Sulfate Under Saline-Alkali Stress In Maize (Zea Mays L.) And Cultivated Barnyardgrass (Echinochloa Frumentacea)

Crop germination,growth and yield formation seriously affected by excessive concentration of saline-alkali ions in the soil,and it is a key issue in the study of enhancing salt-alkali tolerance of crops that improving germination and seedling establishment rates of crops under Soda saline-alkali stress.Soil salinization reduces the effectiveness of Mn,and the physiological mechanisms by which exogenous supplementation of Mn SO₄improves crop growth under Soda saline-alkali conditions are unclear,so two experiments were conducted:Experiment 1 was effects of soaking seed with Mn SO₄solution on the germination and physiological characteristics of maize seeds;Experiment 2 used maize and cultivated barnyard as test materials to investigate the physiological regulation of Mn SO₄on the seedling（V5）of two crops under saline-alkali stress by seed soaking or applying fertilization.The main results were as follows:（1）Saline-alkali stress significantly inhibited the growth of maize germ and radicle,and reduced the seed germination and vitality index.Mn SO₄treatment at 5 mmol/L significantly increased the efficiency of antioxidant system operation of maize shoots under saline-alkali stress,increased the activity of antioxidant enzymes and the content of antioxidant substances such as As A and GSH,reduced the content of reactive oxygen species in plants,promoted the operation of the overall As A-GSH cycle in plants,increased the synthesis of soluble substances in plants,improved the osmotic coordination ability,and reduced the stress-induced lipid peroxidation,thus improving the salinity resistance of maize shoots and effectively improving the germination of seeds.（2）Saline-alkali stress caused above-ground growth in both crops to be inhibited,with more dry matter allocated to the roots and a significant increase in root-to-crown ratio,which increased total N uptake but inhibited the conversion process to N.The nitrate-N content was reduced and the activity of key enzymes for N assimilation decreased,while chlorophyll content was significantly reduced and lowered the Fv/Fm ratio,inhibiting the performance of Y（II）,q P,and ETR on the light response curve.This led to a significant decrease in photosynthetic efficiency and eventually led to the imbalance of carbon and nitrogen metabolism.After the application of Mn SO₄fertilizer or seed soaking treatment,the above-ground growth of the crops was effectively improved,the accumulation of chlorophyll and carotenoids was promoted,the Fv/Fm ratio was increased,the photosynthetic capacity of the seedlings of both crops under saline stress was enhanced.while the root system development was promoted,the plant’s ability to absorb nitrogen was improved,the activity of key enzymes of nitrogen metabolism was enhanced,the accumulation of free amino acids was effectively promoted,and the overall nitrogen assimilation efficiency of the plants was improved.Compared with the two treatment methods,fertilization treatment was more effective in reducing the damage caused by saline stress and balancing their carbon and nitrogen metabolism ability.（3）The cell membrane permeability of seedlings of both crops was damaged by saline-alkali stress,and malondialdehyde content and relative electrical conductivity were increased significantly,while soluble protein and proline content were increased significantly,soluble sugar content were increased in cultivated barnyardgrass,but decreased in maize seedlings.Saline-alkali stress disrupted the ROS balance in both crops,and reactive oxygen radicals accumulated in large amounts,both crops alleviated the stress by increasing antioxidant enzyme activities and As A/DHA,and GSH/GSSG to alleviate the stress.After the application of Mn SO₄fertilizer or seed dipping treatment,it significantly enhanced the scavenging rate of superoxide anion radicals,while promoted the synthesis of osmoregulatory substances such as soluble sugars,regulated osmotic pressure,reduced MDA content and relative electrical conductivity in leaves,and alleviated saline stress injury by increasing the activity of antioxidant enzymes and the content of antioxidant substances.（4）Saline-alkali stress significantly increased sodium ion content in both crops,inhibited the uptake of K,Mn,and Zn,promoted the increase of Ca and Mg content,while no significant change in Cu content.The two Mn SO₄treated crops increased the uptake of K and Mn,significantly reduced the sodium ion content,and Na⁺/K⁺,Na⁺/Ca²⁺,and Na⁺/Mg²⁺were also significantly reduced,alleviating the ion toxicity and osmotic stress caused by excessive sodium ions and high p H to plants under saline-alkali stress.