Abstract: To explore the photosynthetic responses to interaction of light intensity and CO2 concentration and photoinhibition characteristics of different apple canopy shapes is important for guiding to reform the canopy-densed fruit trees in orchards. In the present study，32-year-old apples（Malus × domestica‘Nagafu 2’）of the traditional and dense Round and large canopy（control）and the reformed Open-central canopy based on Round and large canopy were compared carefully by measuring and analyzing the responses of leaf net photosynthetic rate（Pn）to photosynthetically active radiation（PAR）at different leaf surface CO2 concentration（Cs）and leaf Pn to intercellular CO2 concentration（Ci）under different PAR，and the changes of leaf Pn，leaf rate of photorespiration（Pr），reversible component r(qE) and irreversible component r(qI) in nonphotochemical quenching（NPQ）before（8：00–10：00），during（12：00–14：00）and after（16：00–18：00）photoinhibition. The results showed that leaf maximum Pn（Pnmax）increased by 151%（Open-central canopy）and 83.5%（Round and large canopy），and range of light intensity of photosynthesis（light saturation point minus light compensation point）increased by 45.8%（Open-central canopy）and 87.5%（Round and large canopy）of higher Cs（2 000 μmol • mol-1）than common Cs（400 μmol • mol-1）. Maximum carboxylation rate under Rubisco restriction（Vcmax），maximum electron transfer rate under saturated light（Jmax）and utilization rate of triose phosphate（Vtpu）increased with increasing PAR and reached the peak level at PAR of 1 500 μmol • m-2 • s-1，and then decreased slightly due to photoinhibition. Among the three limiting factors，Jmax was the most sensitive one to the changing PAR and the difference in Vtpu was the most significant between Open-central canopy and Round and large canopy. Leaf Pn and Pr of Open-central canopy were significantly higher than that of Round and large canopy，while NPQ of the two canopy shapes was not significant different in 8：00–10：00（before photoinhibition）. Leaf Pn was decreased remarkably，while leaf Pr and r(qE) were enhanced greatly with significantly higher Open-central canopy than Round and large canopy in 12：00–14：00（during photoinhibition）. In 16：00–18：00（after photoinhibition），leaf Pn of Open-central canopy recovered obviously（Pnmax increased by 42.6%）while Round and large canopy did not change significantly. Excitation energy dissipation transferred from photorespiration to thermal dissipation and leaf Pr decreased in Open-central canopy. However，in Round and large canopy，photorespiration was still the mainly way of energy dissipation and leaf Pr increased. In summarize，there was a clear positive interaction to leaf photosynthesis between the increased Cs and enhanced PAR（not beyond saturation point）. Comparing to Round and large canopy，Open-central canopy had significantly improved leaf photosynthetic capacity，more effective photoprotective mechanism by enhancing photorespiration and thermal dissipation during photoinhibition，and obviously recovered leaf net photosynthetic rate after photoinhibition.

Key words: apple, canopy shape, photosynthesis, photosynthetically active radiation, carbon dioxide concentration, interaction, photoinhibition