Temperature-driven yield variation of super hybrid rice across ecological regions: mitigation by nitrogen management...

Improving rice productivity remains essential under land constraints and rising food demand. However, spatial yield variation of super hybrid rice across agroecosystems and the mechanisms driving it is not fully resolved. We evaluated how thermal regimes, nitrogen management and genotype jointly shaped yield differences of super hybrid rice across two ecological regions. Field experiments (2021-2022) used three super-hybrid cultivars - Liangyoupeijiu (LYPJ), Y-liangyou-1 (YLY1) and Y-liangyou-900 (YLY900) - under four N rates (0, 150, 240, and 330 kg ha^-1) at Longhui and Changsha. Averaged across varieties and years, grain yield in Longhui exceeded Changsha by 16.8% (2021) and 26.7% (2022). These site differences were associated with higher temperatures in Changsha during panicle initiation and grain filling, which were accompanied by reductions in spikelets per panicle (~ 5.6%), total spikelets (~ 7.7%) and seed-setting rate (~ 10.6%). Longhui also exhibited greater leaf area index, dry-matter accumulation, and crop growth rate, supporting superior sink formation and grain filling. Partial least squares path modeling indicated that crop growth rate, total dry weight, and seed-setting rate mediated much of the observed yield gap. Nitrogen at 240 and 330 kg ha^-1 narrowed inter-site yield differences by improving yield components and growth traits. Among cultivars, YLY900 achieved the highest yield, while YLY1 showed the greatest cross-site stability. Under the tested conditions, these results suggest that aligning N management with genotype selection relative to local thermal regimes can help reduce temperature-driven yield losses in super hybrid rice.