Root-zone oxygen supply improves lettuce photosynthetic function under waterlogging stress and promotes plant growth

Aerated irrigation alleviates the high soil saturation issue caused by conventional irrigation by delivering oxygen-enriched water to the crop root zone. However, whether it can alleviate plant hypoxia under waterlogging stress remains unclear. In this study, we examined the effects of aeration on the growth, photosynthetic physiological activities, and gene expression of lettuce (Lactuca sativa L.) under different waterlogging durations (0, 4, and 8 days). The results indicate that under short-term waterlogging stress (≤4d), plants reduce the accumulation of reactive oxygen species by increasing the activity of the antioxidant system, and aeration does not significantly enhance plant growth. If waterlogging lasts for more than 8 days, non-aerated treatment leads to significant accumulation of reactive oxygen species (O₂^- and H₂O₂ increased by 50.68% and 37.76%, respectively), cell membrane damage (MDA increased by 32.31%), and damage to the photosynthetic system. At this point, aerated irrigation can significantly alleviate stress by increasing the expression of Psb and rbcS genes in leaves, maintaining normal photosynthetic function of lettuce, and increasing lettuce biomass by 36.70% compared to non-aerated treatment. Therefore, in actual waterlogging event management, aeration irrigation should be prioritized for long-term waterlogging (8d) areas. Twelve gene co-expression modules were identified using the weighted gene co-expression network analysis (WGCNA) method. Three modules specifically related to lettuce waterlogging stress were identified through correlation analysis with physiological indicators. The five hub genes (HPR3, GGPS1, THI1, rbcS, G6PD) in the yellow module have become sensitive genes that lead to a decrease in photosynthetic efficiency under waterlogging stress. The hub genes of brown and green modules (PPC4, FRO7, ispH, ERF1b, AUF2) showed an increase in expression levels with the passage of waterlogging time. These five genes may be the core genes for improving lettuce waterlogging tolerance. This study explored the molecular mechanism of lettuce's tolerance to waterlogging stress at the transcriptome level, providing deeper insights into the alleviating effect of aerated irrigation on waterlogging stress.