Analysis of the Multi-Factor Mechanism of High-pH Saline-Alkali Paddy Fields Restricting Growth and Yield in Rice

Global soil salinization threatens crop productivity, food security, and ecosystems. In Northeast China’s Songnen Plain, high-pH saline-sodic soils impose severe alkali stress on plants. The yield of rice (Oryza sativa) is severely restricted. Our study established gradient saline-alkali paddy fields with three different pH values (7.81, 8.52, and 9.23) to analyze the correlations among plant growth, soil microorganisms, and yield. After three years’experiments, the results revealed that increasing pH reduced the growth indicators of rice. Severe saline-alkali paddy fields experienced damaged rice root systems, and the Malondialdehyde (MDA) content and Reactive Oxygen Species (ROS) accumulation significantly increased. In the moderate saline-alkali paddy field, the root system enhanced the activity of antioxidant enzymes to alleviate the damage caused by the alkaline stress. High pH enhanced the CO32−, HCO3−, and Na+ levels in the soil, but the soil nutrient indicators were reduced. The abundance and diversity of soil microorganisms also decreased with increasing pH and were strongly correlated with soil physical and chemical properties. Moreover, the theoretical yield and its constituent factors significantly decreased with increasing pH, along with reduced seed testing indicators. These findings provide a complete theoretical and practical basis for an in-depth and comprehensive clarification of the plant-soil-microbe synergistic mechanism affecting rice yield from multiple perspectives.