Zani et al. (Research Articles, 27 November 2020, p.1066) propose that enhancement of deciduous tree photosynthesis in a CO2-enriched atmosphere will advance autumn leaf senescence. This premise is not supported by consistent observations from free-air CO2 enrichment (FACE) experiments. In most FACE experiments, leaf senescence or abscission was not altered or was delayed in trees exposed to elevated CO2.