Abstract: After exposing fully expanded poplar (Populus alba L.) leaves to continuous irradiation,the photosynthetic rate and isoprene emissions increased.Continuous irradiation also enhanced the levels of total respiration and the capacities of the cytochrome and alternative respiratory pathways.Pretreatments with cytochrome and alternative respiratory pathways inhibitors,salicylhydroxamic acid and KCN,decreased the photosynthetic rate and isoprene emissions.These treatments also decreased the immediate quantum yield of PSⅡ electron transport and photochemical quenching.These results suggest that respiration plays a role in mediating photosynthesis and isoprene emissions.