Drill Seeding and 5-ALA Synergistically Maintain the Photosynthetic System and Ion Balance of Rice Seedlings to Alleviate Salt Stress

Background Seedling raising of rice ( Oryza sativa L.) is a critical step in rice cultivation, and salt stress significantly impedes the growth of rice seedlings, while 5-aminolevulinic acid (5-ALA) plays a vital role in plant responses to various abiotic stresses. This experiment combines agronomic practices with chemical regulation to investigate the effects of drill sowing and 5-ALA on the photosynthetic system and ionic homeostasis of rice seedlings under salt stress. Results The results demonstrated that salt stress led to substantial accumulation of Na⁺ and Cl⁻ in rice seedling leaves, which disrupted the photosynthetic system and significantly inhibited seedling growth. Exogenous application of 5-ALA increased the content of chloroplast synthesis precursors, promoted the synthesis of photosynthetic pigments, reduced the accumulation of Na⁺ and Cl⁻, enhanced the levels of K⁺ and Ca²⁺, improved antioxidant enzyme activity, and mitigated oxidative damage. Consequently, it improved gas exchange parameters and chlorophyll fluorescence characteristics, and thus increased carbohydrate accumulation. Under drill sowing conditions, the application of 5-ALA resulted in higher levels of chloroplast synthesis precursors and carbohydrate accumulation compared to broadcast sowing. Under salt stress, this provided more energy substrates for chlorophyll synthesis and photosynthetic system repair, thereby enhancing peroxidation scavenging capacity, maintaining the stability of the photosynthetic system and ionic homeostasis, and resulting in stronger salt tolerance than broadcast sowing. Conclusion In conclusion, the combination of drill sowing and foliar application of 5-ALA synergistically maintained the photosynthetic system and ionic balance in rice seedlings under salt stress, improving their salt tolerance. This study provides a theoretical basis for optimizing sowing methods and chemical regulation in rice seedling cultivation in saline-alkali soils.