Nitrogen supply mitigates heat-driven potato yield loss by sustaining radiation use efficiency and dry matter partitioning to tubers

Heat episodes increasingly constrain potato ( Solanum tuberosum L.) productivity, yet how nitrogen (N) status modulates heat-induced limitations in canopy function, radiation use efficiency ( RUE ), and source–sink allocation remains insufficiently resolved. We conducted a pot experiment in controlled climate chambers using two temperature regimes (control, T0; heat stress, T1) combined with three N rates (0, 50 and 150 kg ha - ¹; N0, N1 and N2) in a split-plot design. Compared with T0, heat stress significantly raised canopy temperature, reduced chlorophyll status ( SPAD ), and decreased RUE by 15.4%, and restricted the translocation of photoassimilates from shoots to tubers, which resulted in a 42.1% decline in tuber dry weight at harvest. Crucially, while heat stress drove a 31.9% reduction in RUE under N-deficient conditions (N0), this penalty was effectively neutralized under high N (N2). Furthermore, sufficient N supply alleviated the heat-induced restriction on dry-matter translocation, reducing the biomass fraction retained in shoots from a 6.9% excess at N0 to only 3.9% at N2, thereby facilitating more effective dry matter allocation to tubers under thermal stress. Consequently, heat-induced tuber yield loss was alleviated by N, with dry weight reductions declining from 55% (N0) to 33% (N2). Overall, sufficient N supply mitigated heat-induced yield loss in potato primarily by sustaining RUE and dry matter partitioning to tubers during bulking, providing physiological insight into how N status supports tuber yield formation under heat stress.