Seed-applied Ti₃C₂ MXene quantum dots enhance root–water coordination and increase maize grain yield under deficit irrigation

Context In arid spring maize systems, crop productivity is often challenged by early-season exposure to temperatures below the maize base temperature of 10 °C and by limited seasonal water supply. Seed-applied interventions may improve crop performance if they enhance early establishment and maintain the root, water, and canopy functions that support yield formation. However, the field-level agronomic value of Ti₃C₂ MXene quantum dots (MQDs) as a seed coating remains insufficiently tested. This study evaluated whether MQDs seed coating could improve maize stand establishment, sustain root–water–canopy function, and increase grain yield under contrasting sowing dates and irrigation regimes in an arid field environment. Methods A two-year field experiment was conducted in Northwest China using a split-split-plot design with two sowing dates, three irrigation regimes, and two seed treatments. The irrigation regimes were full irrigation (HI), moderate deficit irrigation at 75% of HI (MI), and severe deficit irrigation at 50% of HI (LI). The seed treatments were a blank-coated control and MQDs seed coating. Emergence dynamics, stand establishment, antioxidant capacity, root morphology, rhizosphere bacterial community composition, soil and plant water status, chlorophyll status, photosynthetic rate, leaf area index, aboveground biomass, anthesis–silking interval, yield components, grain yield, and net return were measured. Results MQDs seed coating consistently improved early establishment across treatment combinations. Compared with the blank-coated control, MQDs increased maximum emergence percentage by 3.4%–6.8% and stand establishment rate by 3.6%–5.9%, while shortening the time to 50% emergence by up to 0.41 d. Irrigation strongly affected yield formation, and MQDs increased grain yield by 3.8%–18.8% across treatment combinations, with larger relative benefits under deficit irrigation. Under early sowing and severe deficit irrigation, MQDs increased grain yield from 8747.11 to 10,186.06 kg ha⁻¹ in 2024 and from 8171.89 to 9708.49 kg ha⁻¹ in 2025, representing increases of 16.5% and 18.8%, respectively. Yield improvement was accompanied by higher grain number per ear and 1000-grain weight, indicating that MQDs supported both sink establishment and grain filling. MQDs also enhanced seedling antioxidant capacity, increased total root length and root surface area, maintained less negative leaf water potential under deficit irrigation, increased net photosynthetic rate by up to 26.6%, promoted leaf area and biomass accumulation, and was associated with shifts in rhizosphere bacterial community composition at V6. Conclusion MQDs seed coating improved maize stand establishment and supported yield formation under arid, water-limited field conditions. The agronomic benefit was most consistently expressed through stronger establishment and coordinated improvements in root development, plant water status, canopy photosynthetic function, biomass accumulation, and yield components. These results indicate that MQDs seed coating has potential as a seed-based supportive strategy for improving spring maize productivity under deficit irrigation, although the causal physiological mechanisms, microbiome contribution, dose response, environmental fate, and broader field applicability require further verification.