Waterlogging Priming at Tillering Stage Confers Stronger Tolerance to Wheat Plants Waterlogged During Anthesis

Waterlogging stress, particularly during flowering, severely constrains wheat production, yet the optimal timing and frequency of waterlogging priming and its linkage to post-stress nitrogen acquisition remain unclear. We conducted pot experiments under a glasshouse over two consecutive growing seasons (2022/23 and 2023/24) using the Japanese bread wheat cultivar Norin 61. Eight treatment combinations were established with or without waterlogging priming applied at the tillering, stem elongation, and booting stages, followed by waterlogging for 5 days (2022/23) and 4 days (2023/24) during the flowering stage. To quantify post-stress nitrogen dynamics, 15N-labeled ammonium sulfate was applied immediately after waterlogging termination at flowering, and 15N uptake and its allocation to plant organs and grains were determined during grain filling and at harvest. Compared to the non-primed treatment, treatments that included tillering-stage priming consistently maintained higher leaf SPAD values, photosynthetic performance, and increased thousand-grain weight across both seasons, and grain yield increased by 54.8–80.6% in 2022/23 and 125.8–159.7% in 2023/24. These treatments also showed higher post-stress 15N content and greater 15N allocation to grains. Overall, tillering-stage waterlogging priming was associated with improved tolerance to flowering-stage waterlogging in wheat through the maintenance of post-stress nitrogen uptake capacity and nitrogen allocation to grains.