This study tested the hypothesis that brassinosteroids (BRs) mediate moderate soil‐drying (MD) to alleviate spikelet degeneration under high temperature (HT) stress during meiosis of rice (Oryza sativa L.). A rice cultivar was pot‐grown and subjected to normal temperature (NT) and HT treatments during meiosis, and two irrigation regimes including well‐watered (WW) and MD were imposed to the plants simultaneously. The MD effectively alleviated the spikelet degeneration and yield loss under HT stress mainly via improving root activity and canopy and panicle traits including higher photosynthetic capacity, tricarboxylic acid cycle activity, and antioxidant capacity than WW. These parameters were regulated by BRs levels in plants. The decrease in BRs levels at HT was due mainly to the enhanced BRs decomposition, and the MD could rescue the BRs deficiency at HT via enhancing BRs biosynthesis and impeding decomposition. The connection between BRs and HT was verified by using rice BRs‐deficient mutants, transgenic rice lines, and chemical regulators. Similar results were obtained in the open‐air field experiment. The results suggest that BRs can mediate the MD to alleviate spikelet degeneration under HT stress during meiosis mainly via enhancing root activity, canopy traits, and young panicle traits of rice.
This study investigated whether and how irrigation regimes interact with nitrogen (N) application rates to mediate the grain yield, N use efficiency (NUE) and water use efficiency (WUE) in rice and to understand the underlying mechanism. A field experiment was conducted with two irrigation regimes, continuously flooded (CF) and alternate wetting and moderate drying (AWMD), and three N application rates, 120 kg ha−1 N (a low N rate, LN), 240 kg ha−1 N (a medium N rate, MN) and 360 kg ha−1 N (a high N rate, HN) in 2021 and 2022. The results showed that the grain yield exhibited the lowest values at the LN, regardless of the irrigation regime, while it was the highest at the MN when the CF regime was adopted. The grain yield was comparable between the MN and HN regarding the AWMD regime. AWMD significantly increased the grain yield, NUE and WUE compared to CF at the same N rate, which was attributed to a higher photosynthetic rate, improved population quality, enhanced nonstructural carbohydrate remobilization from stems to grains during grain filling, and elevated activities of enzymes involved in N assimilation in the roots. The results suggest that an AWMD regime combined with MN treatment could pronounce a synergistic interaction on the grain yield, NUE and WUE in rice by improving root and shoot physiological performances.
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