Synergistic effects of density and nitrogen on yield mediated by enhanced chlorophyll fluorescence and photosynthetic performance compensating for irrigation reduction in maize

Agricultural green development aims to sustain high yields with fewer resources. While high planting density boosts yield, it can suppress individual plant photosynthesis. However, it remains unclear whether high density benefits can offset the constraints of reduced water and nitrogen, or how chlorophyll fluorescence regulates light capture and carbon assimilation in densely planted maize. A two-year maize field experiment investigated the interaction of reduced irrigation (W1, 20% less), reduced nitrogen (N1, 25% less), and increased planting densities by 30% D2 and 60% D3. The results showed that increasing density significantly raised ear number per unit area and improved pre-heading dry matter translocation to ear. Specifically, the combination of reduced irrigation with conventional nitrogen and a 30% higher density (W1N2D2) increased grain yield by 13.00% and biomass by 8.64% compared to the conventional treatment (W2N2D1), with significant differences observed ( P < 0.05). This is consistent with an increase in light-harvesting efficiency as indicated by SPAD and chlorophyll fluorescence indices. Key photosynthetic genes highly expressed from the V12 to R2 stages, were positively correlated with grain yield and aligned with peak dry matter accumulation. In conclusion, synergistically increasing planting density by 30% under conventional nitrogen application effectively compensates for reduced irrigation. This strategy optimizes canopy architecture and mitigates the suppression of individual plant photosynthesis, thereby enhancing yield under water-saving conditions. This approach provides a practical pathway for achieving the goals of agricultural green development. • A 30% density increase offset maize yield loss from reduced water and N. • The peak photosynthetic enzyme expression at V12-R2 matched the peak dry matter accumulation. • D2 promotes dry matter translocation and dry matter partitioning to the ear. • W1N2 enhanced the maximum photochemical efficiency of PSII, electron transport rate, and normalized area.