Development stage-specific recovery of remedial nitrogen fertilizer application after waterlogging in maize through photosynthetic capacity and nitrogen allocation

Nitrogen (N) application at jointing stage (V6) led to significantly better recovery compared to that at blister stage (R2) under waterlogging stress (WS). Under WS, N application restored photosynthetic capacity at V6 by enhancing photosynthetic enzyme activity, thereby increasing grains number. Under WS, N application promoted N allocation to grain at R2 by activating protein synthesis of grain, which enhanced grain sink capacity. Waterlogging stress (WS) significantly threatens summer maize production. Although supplemental nitrogen (N) fertilization is a common remediation strategy, the differences in N regulation pathways across developmental stages are still unclear. The maize hybrid ‘Zhongkeyu 505’ was used as the experimental material in a 3-year field localization experiment investigating the responses and N-mediated recovery pathway in maize at the jointing stage (V6) and blister stage (R2) to WS. Over three experimental years, compared to control, WS significantly decreased grain yield at V6 and R2 by an average of 27.6 and 23.0%, respectively. Structural equation modeling showed that WS decreased grain number at V6 by inhibiting leaf photosynthetic capacity, and reduced grain capacity at R2 by limiting N allocation to grains. However, post-waterlogging nitrogen application (WF) effectively mitigated these losses, increasing grain number by 19.1% at V6 and improving grain sink capacity by 23.4% at R2. The recovery at V6 was driven by enhanced photosynthetic capacity with average increases of 23.6% in total chlorophyll content, 36.3% in phosphoenolpyruvate carboxylase activity, and 24.8% in Rubisco activity. Differently, the recovery at R2 was due to improve N utilization, where N allocation in grains increased to 73.1%, and nitrate reductase and glutamine synthetase activities in grains increased by an average of 31.7 and 35.6%, respectively. Transcriptomic analysis further confirmed upregulation of protein-processing genes (e.g. hsp18a and hsp18c ), facilitating N allocation and utilization. In conclusion, the N-mediated recovery pathway varied across maize development stages, with the photosynthetic capacity and grain number restored at V6 and N allocation to grains and sink capacity was increased at R2. This study will provide significant theoretical and practical value for enhancing tolerance in maize to WS at V6 and R2.