Effects of simulated seawater intrusion-induced salt stress and the recovery process on growth, antioxidant system, and photosynthesis of rice, and the alleviating effect of Pro-Ca

Saltwater intrusion is a common threat to coastal agriculture. This study investigated the mitigating and restorative effects of exogenous prohexadionecalcium (Pro-Ca) on rice under simulated saltwater intrusion. Salt-tolerant Chaoyou 1000 and salt-sensitive Huanghuazhan were treated with 100 mg·L⁻¹ Pro-Ca at the four-leaf-one-bud stage. Physiological responses were analyzed during stress (D1–D4) and recovery (FD4). Salt stress significantly inhibited rice growth, reduced biomass, induced oxidative damage, and impaired photosynthesis and photosystem II (PSII) activity, with maximum damage at D4. Exogenous Pro-Ca enhanced stress tolerance by activating antioxidant enzymes and the ascorbate-glutathione (AsA-GSH) cycle, effectively scavenging reactive oxygen species (ROS) and protecting cell membrane integrity. Additionally, Pro-Ca maintained PSII activity and improved light use efficiency, ensuring photosynthetic function. During recovery (FD4), Pro-Ca-treated plants showed superior physiological recovery compared to salt-stressed controls. The exogenous application of Pro-Ca effectively alleviates salt stress damage caused by seawater intrusion in rice. It enhances salt tolerance by strengthening the antioxidant defense system and maintaining photosynthetic function, while significantly promoting the recovery of physiological status during the post-stress rehabilitation phase.