Comparative Study of Mycorrhizal Rice Seedlings Cultivated Under Suitable and High-Phosphorus Environment in Resisting Saline–Alkali Stress

Rice seedlings are typically grown in high-phosphorus nursery soils in practice, which reduces rice root growth and the plant’s ability to adapt to adverse conditions after transplantation to the paddy field. Thus, it is important to improve rice root development in high-phosphorus nursery soils. Rice root developments are closely connected with soil microorganisms. Arbuscular mycorrhizal fungi (AMF) can promote rice root growth and help improve rice performance in resisting adverse conditions. To illustrate the mechanisms of rice seedlings with AMF inoculation under suitable and high-phosphorus nursery soils in resisting adverse conditions, rice seedlings were cultivated in suitable and high-phosphorus nursery soils inoculated with AMF JD5 (Paraglomus sp.) and transplanted into soda saline–alkaline soils following successful AMF inoculation. Results showed that under high-phosphorus conditions, AMF JD5 inoculation significantly promoted plant height and root elongation, likely through increased total chlorophyll content. Concurrently, proline content was reduced, whereas soluble sugar and soluble protein contents were elevated, indicating alleviation of osmotic stress induced by saline–alkaline conditions. Moreover, AMF JD5-inoculated seedlings exhibited increased CAT activity, which efficiently scavenged reactive oxygen species (ROS) generated under salt–alkaline stress and reduced lipid peroxidation. However, thiobarbituric acid reactive substances (TBARS) content was significantly decreased with AMF inoculation in high-phosphorus conditions. Collectively, these findings suggest that AMF JD5 inoculation in high-phosphorus nursery soils establishes a physiological and biochemical foundation that maintains rice resilience against saline–alkaline stress throughout early growth.