Effects Of Arbuscular Mycorrhizal Fungi On Growth And Salt And Alkali Tolerance Of Sunflower

Soil salinization has become a worldwide ecological and environmental problem.The area of saline-alkali soil in Inner Mongolia accounts for 6.45%of the total area,and it is still increasing at the rate of 150,000²00,000 mu per year.Soil salinization causes soil fertility decline and affects plant growth,which has become one of the important factors restricting the development of agriculture and animal husbandry.Studies have shown that AM fungi can significantly improve salt and alkali tolerance of sweet soil plants,but there are few studies on the effects and mechanisms of AM fungi on salt-alkali tolerance of economic crop Helianthus annuus L.A greenhouse pot experiment was conducted,and the salt-tolerant economic crop sunflower was used as a test plant to simulate different degrees of salt stress(NaCl concentration was 0 g·kg^-1,0.5 g·kg^-1,1.0 g·kg^-11 and 1.5 g·kg^-1)and different types of saline-alkali stress?control,NaCl,Na₂SO₄,NaCl+Na₂SO₄,NaHCO₃+NaCl,NaHCO₃+Na₂SO₄,Na₂CO₃+NaCl,Na₂CO₃+Na₂SO₄?.The effects of AM fungi F.mosseae on sunflower growth and salt-alkali tolerance were studied.The results showed that NaCl concentration could significantly affect the infection of sunflower roots by F.mosseae.The average mycorrhizal infection rate ranged from 51.99%to 68.85%,and the infection rate was the highest when treated with 1.0 g·kg^-1.The increase of NaCl concentration significantly promoted the absorption and accumulation of Na⁺and the content of MDA and proline in sunflower.Salinity stress significantly decreased shoot and total dry weight of sunflower,the activity of POD,the net photosynthetic rate?Pn?,transpiration rate?Tr?and the water use efficiency.Under different concentrations of NaCl stress,AM fungi significantly increased the total dry weight of sunflower by 16.95%to 28.97%,P concentrations by 33.77%to 54.29%,the net photosynthetic rate?Pn?by 7.70%to 80.00%,transpiration rate?Tr?by 7.27%to 32.53%,the water use efficiency by 8.93%to14.97%,Na⁺content in shoot and root and POD activity in shoot.AM fungi significantly decreased C:P and N:P in shoot and root,proline content by 80.26%to87.05%,and soil EC value by 3.17%to 10.89%under salinity stress.Under different saline-alkali stress,the mycorrhizal infection rate of sunflower inoculated with F.mosseae was 14.50%³2.17%.The order of mycorrhizal dependencewasNa₂CO₃+Na₂SO₄>NaHCO₃+NaCl>Na₂CO₃+NaCl>NaHCO₃+Na₂SO₄>NaCl+Na₂SO₄>Na₂SO₄>control>NaCl.Different kinds of saline-alkali stress significantly inhibited the growth of sunflower,enhanced the absorption and accumulation of Na⁺,and significantly increased the EC value of rhizosphere soil.AM fungi significantly increased the total dry weight and strong seedling index of sunflower by 26.08%to 74.54%and 7.65%to 93.45%,P concentration in shoot and root by 70.37%to 125.00%and 61.54%to 88.37%,Na⁺content in root by 50.04%to 83.73%,and the net photosynthetic rate Pn by 15.41%to 20.27%.AM fungi significantly decreased Na⁺concentration in shoot by 34.29%to 48.53%and cell membrane permeability by 26.47%to 51.49%.The results showed that inoculation of AM fungi could significantly promote the adaptability of sunflower to different degrees of salt stress or different types of salt-alkali stress.Its mechanism was mainly through promoting the absorption and utilization of nutrients and water,improving photosynthesis and antioxidant capacity of plants,regulating osmotic substance content and reducing cell membrane damage to enhance salt-alkali tolerance of plants.The results provide basic data and technical support for promoting the development,utilization and ecological restoration of saline-alkali soil.