Abstract: By using a portable photosynthetic system (CIRAS-2), this paper studied the photosynthetic characters of 3-year-old Cotinus coggygria var. cinerea under effects of different soil water regime (enough supply, light stress, medium stress, and heavy stress) and light intensity. Soil water regime had significant effects on the photosynthetic parameters of C. coggygria. With increasing drought stress, the net photosynthetic rate, transpiration rate, and apparent yield all declined apparently, while the light compensation point increased. The highest water use efficiency was found under light water stress (soil relative water content being about 60%-65%). C. coggygria had higher net photosynthetic rate and higher water use efficiency under a wide range of high light intensity (photosynthetically active radiation being 1000-1800 μmol·m^-2·s^-1), but had lower efficiency of light absorbance and conversion, i.e., lower apparent quantum yield, under low light intensity, which was declined more significantly when the soil water stress was intensified.

Key words: Cotinus coggygria  var. cinerea, soil water stress, photosynthesis, transpiration rate, water use efficiency, canopy stomatal conductance, photosynthetically active radiation, vapor pressure deficit, soil water content., sap flow