Sugar Accumulation Drives Elevated CO₂‐Induced Senescence in Solanum tuberosum

Elevated CO 2 (eCO 2 ) can enhance plant growth, but it may also accelerate senescence, which could offset the growth benefits. Phosphorus (P) supply can enhance the photosynthetic rate under eCO 2 conditions and promote biomass accumulation. To explore the mechanisms behind eCO 2 ‐induced senescence and the potential mitigation through P supply, pot experiments were conducted under low and high P conditions during spring and autumn. The eCO 2 ‐induced senescence was remarkable irrespective of P supply in spring, frequently over the optimum temperature (20°C), resulting in a rather lower biomass under eCO 2 than under ambient CO 2 (aCO 2 ). In contrast, in autumn, eCO 2 enhanced biomass at optimal temperatures, particularly under high P conditions. Although leaf C/N ratios were similar under both CO 2 levels in late spring, glucose concentrations were significantly higher under eCO 2 , indicating that sugar accumulation, rather than nitrogen deficiency, contributed to senescence. Additionally, chlorophyll degradation was delayed under high P conditions, though P fertilization did not prevent senescence. These results suggest that yield reductions caused by eCO 2 ‐induced senescence cannot be mitigated by increasing P supply, especially under non‐optimal temperature conditions.