To address the dual challenges of water scarcity and rising demand for premium rice, this study investigated the synergistic effects of mild alternate wetting and drying (Mild AWD) irrigation combined with wheat straw biochar application on rice yield and grain quality. A two-year field experiment (2023–2024) was conducted with the hybrid rice cultivar Yongyou 2640, with two irrigation regimes: continuous flooding (CF) and Mild AWD (re-irrigation at a soil water potential of –10 to –15 kPa at 15–20 cm depth), with or without a one-time biochar application (10 t ha⁻¹). The results showed that co-application of Mild AWD and biochar significantly increased grain yield by 18.7% in 2023 and 13.4% in 2024 compared to CF alone. It also comprehensively improved grain quality: milling quality (head rice rate increased by 23.1–24.6%), appearance quality (chalkiness reduced by 36.4–38.2%), cooking and eating quality (higher peak viscosity and lower gelatinization temperature and enthalpy), and nutritional quality (increased glutelin and decreased prolamin content and starch digestion). These improvements were attributed to enhanced root activity alongside leaf photosynthetic rate, which promotes the accumulation of photoassimilates in vegetative organs and their translocation to grains. Moreover, elevated activities of key starch synthases further enhanced starch biosynthesis and accumulation, which underpinned the improved yield and superior quality. We also identified that a minimum soil water potential of –10 to –15 kPa at a depth of 15–20 cm represents the optimal threshold for Mild AWD in rice production. This research provides a cultivation approach for synergistically producing high-yield, high-quality rice, which shows promising potential for scalable implementation.

This study investigated the role of jasmonates (JAs) in mitigating the impairment of high temperature (HT) stress-induced spikelet opening in photo-thermosensitive genetic male-sterile (PTGMS) rice under controlled moderate soil drying (MD). Two PTGMS rice varieties were grown under normal temperature (NT) and HT conditions, paired with either well-watered (WW) or MD strategies during anthesis, in both controlled-climate pot and open-air field conditions over multiple years. The MD treatment demonstrated significant protective effects compared to the conventional WW regime under HT stress, which significantly reduced the levels of JAs in lodicules and worsened spikelet opening impairment and hybrid seed yield loss. The MD regime enhanced the accumulation of JAs in lodicules, effectively alleviating HT-induced spikelet opening impairment and hybrid seed yield reduction. This protective mechanism operates through multiple pathways: (1) promoting starch hydrolysis into soluble sugars, (2) upregulating the expression of aquaporin genes, and (3) enhancing antioxidant capacity, thereby maintaining cellular osmotic and redox homeostasis in the lodicules. The crucial role of JAs in this mechanism was confirmed using JA-deficient mutants, transgenic rice lines with varying JA biosynthetic capacities, and exogenous applications of JAs. These findings indicate that MD is a more effective cultivation strategy than traditional WW in protecting PTGMS rice from HT stress, which is achieved by modulating levels of JAs to maintain osmotic and redox homeostasis in the lodicules, thus improving spikelet opening and hybrid seed yield under HT stress during anthesis.

Globally recurrent extreme high temperature (HT) events severely limit rice production. This study investigated whether a controlled moderate soil drying (MD) could replace the conventional well-watered (WW) regime to more effectively mitigate HT stress on pistil fertilization in photo-thermosensitive genetic male-sterile (PTGMS) rice, and examined the role of brassinosteroids (BRs). Two PTGMS rice varieties were cultivated under normal temperature (NT) and HT conditions, paired with WW and MD strategies during anthesis. In the conventional WW regime, waterlogging reduced BR levels in roots and pistils due to excessive decomposition, weakening active water uptake driven by root activity and failing to alleviate transpiration-pulled passive water extraction hampered by restricted stomatal openings. Thereby, it caused water imbalance in plants and weakened pistil function due to a suppressed ascorbate-glutathione (AsA-GSH) cycle and hyperactive nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity. This exacerbated pistil fertilization impairment and hybrid seed yield loss under HT stress. Conversely, by promoting BR synthesis and inhibiting its decomposition in roots and pistils, the MD strategy enhanced root activity and transpiration-driven water uptake. It maintained plant water balance and supported pistil function by suppressing NOX activity and enhancing AsA-GSH cycle-driven redox homeostasis. Thus, it mitigated HT-induced pistil fertilization impairment and hybrid seed yield loss. The precise function of BRs in moderating the protective effects of MD against the detrimental impacts of HT stress on pistil fertilization in PTGMS rice was confirmed through genetic and chemical approaches. Consequently, a controlled MD method proved more effective than the conventional WW regime in alleviating HT stress on pistil fertilization in PTGMS rice by promoting BR enhancement.

This study examined the involvement of cytokinins in the process by which moderate water limitation (MWL) mediates nitrogen (N) remobilization from source to sink during the grain-filling phase in wheat. Field experiments were performed using N application rates of low (LN), medium (MN), and high (HN). Two soil moisture regimes were implemented for each N rate: conventional well-watered (CWW) and MWL post anthesis. The MWL application optimized N, total free amino acids (FAA), and trans-zeatin (Z)+trans-zeatin riboside (ZR) reallocation from the source organs (stems and leaves) to the sink organ (spikes) in wheat. Compared to those in the CWW regime, the activities of proteolytic enzymes, including endopeptidase, carboxypeptidase, and aminopeptidase within stems and leaves, and the expression levels of total FAA transporter genes in spikes were significantly elevated in the MWL regime, showing a close correlation with the Z+ZR levels in the spikes. Application of kinetin to stems and leaves significantly inhibited proteolytic enzyme activities, promoting N retention in stems and leaves, decreasing N accumulation in the sink organ, and reducing the N harvest index. In contrast, applying kinetin to spikes significantly upregulated expression levels of FAA transporter genes, reducing N retention in stems and leaves, increasing N accumulation in the sink organ, and raising the N harvest index. Such facilitation induced by the MWL in the remobilization of N from source to sink was greater at HN than at LN or MN. Results demonstrate that post-anthesis MWL can significantly intensify the remobilization of N from source to sink, while also synergistically enhancing grain yield and N use efficiency through strategically redistributing cytokinins (Z+ZR) between source and sink in wheat.