Photosynthetic gas-exchange and PSII photochemical acclimation to drought in a native and non-native xerophytic species (Artemisia ordosica and Salix psammophila)

•PSII photochemical response to anomalous drought was examined via ChlF fluorescence.•Shrub acclimated to drought by stomatal-regulation mechanism.•Shrub acclimated to drought also by PSII non-photochemical quenching mechanism.•Water conservation strategy was found in the acclimation to drought.•Native species performed better than the non-native in response to severe drought. The mechanisms of plant photosynthetic acclimation to drought remains incomplete. We examined the photosynthetic performance through plant photosystem-fluorescence response to a long-lasting, anomalous summer drought (i.e., lasting for 61 days, with soil water content