Sugar Accumulation Drives Elevated CO₂-Induced Senescence in Solanum tuberosum

Elevated CO₂ (eCO₂) 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 eCO₂ conditions and promote biomass accumulation. To explore the mechanisms behind eCO₂-induced senescence and the potential mitigation through P supply, pot experiments were conducted under low and high P conditions during spring and autumn. The eCO₂-induced senescence was remarkable irrespective of P supply in spring, frequently over the optimum temperature (20°C), resulting in a rather lower biomass under eCO₂ than under ambient CO₂ (aCO₂). In contrast, in autumn, eCO₂ enhanced biomass at optimal temperatures, particularly under high P conditions. Although leaf C/N ratios were similar under both CO₂ levels in late spring, glucose concentrations were significantly higher under eCO₂, 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 eCO₂-induced senescence cannot be mitigated by increasing P supply, especially under non-optimal temperature conditions.