Optimized soil drying alleviates high-temperature stress on yield formation by enhancing brassinosteroid-mediated root-shoot functional synergy in post-anthesis rice

Context or problem: High-temperature (HT) stress severely inhibits grain yield formation in post-anthesis rice, and water management is crucial for mitigating this stress. However, it remains unclear whether and how an optimized moderate soil drying (MD), which maintains the soil water potential (Ψ_soil) at −10 ± 5 kPa within the 15–20 cm soil depth, can mitigate HT impacts more effectively than conventional well-watered (WW) irrigation.

Objective: The study aims to (1) determine whether the optimized MD regime (Ψ_soil = −10 ± 5 kPa at 15–20 cm soil depth) can mitigate yield losses under post-anthesis HT stress, (2) investigate the underlying mechanisms from the perspective of root-shoot functionality, with particular focus on the role of brassinosteroids (BRs), and (3) evaluate the potential of this irrigation strategy for alleviating HT stress on rice yield formation.

Methods: A two-year field experiment was conducted with a commonly grown local rice cultivar, comparing MD (Ψ_soil = −10 ± 5 kPa at 15–20 cm soil depth) and WW under ambient temperature (AT) and HT stress imposed post-anthesis. Grain yield, root water uptake and energy/redox status, stem non-structural carbohydrate (NSC) remobilization, grain starch synthesis, and BRs levels in roots, stems, and grains were assessed.

Results: The optimized MD regime significantly mitigated HT‑induced yield losses, increasing grain yield by 21.8–23.9% under HT compared to WW, primarily through increased grain weight and filling rate. Mechanistically, MD enhanced root BRs accumulation, which restored root energy and antioxidant capacity, maintained water uptake, and improved shoot water status. MD also elevated BRs in stems and grains, promoting stem‑to‑grain non‑structural carbohydrate remobilization and sustaining grain starch synthesis. Genetic evidence further confirmed that BRs play a causal role in mediating these MD‑induced effects.

Conclusions: The optimized MD regime (Ψ_soil = −10 ± 5 kPa at 15–20 cm soil depth) represents an innovative, water-saving irrigation strategy that effectively mitigates HT stress on post-anthesis rice. It enhances root-shoot functional synergy by systemically elevating BRs, which coordinate root water uptake, stem NSC remobilization, and grain starch synthesis, thereby maintaining high grain yield under HT stress.

Implications or significance: Amid escalating global temperatures and water scarcity, this optimized MD strategy (Ψ_soil = −10 ± 5 kPa at 15–20 cm soil depth) offers a practical and effective solution for sustainable rice production.