Solidago canadensis, which poses a serious threat to the regions it has invaded, causes considerable economic loss every year throughout the world. Different methods are used to control invasive species, among which chemical control is widely used. However, herbicide application may have a negative effect on the growth of neighboring native species. Recently, glyphosate, which has high efficiency and low toxicity, has become widely used both in China and abroad. In the present study, distinctive photosynthetic responses to glyphosate treatment in the invasive (S. canadensis) and native (Imperata cylindrica) plants were compared to investigate the impact of herbicide application on alien and indigenous plants. Plants were grown in monoculture and mixed culture for a 21-day period, and growth and photosynthetic characteristics were determined under four different concentrations of glyphosate (0, 0.6, 1.2, 1.8mL/L). The results were as follows:(1) Glyphosate significantly inhibited the growth of S. canadensis and I. cylindrica (P < 0.05). Cumulative growth in height and the number of green leaves of S. canadensis were apparently reduced with increasing concentration of glyphosate, while withering rate of tillers and leaves of I. cylindrica were obviously increased. Imperata cylindrica showed more sensitivity to glyphosate treatment than S. canadensis; it turned yellow from 0.6mL/L glyphosate concentration, and the withering rate exceeded 50% with 1.2mL/L glyphosate concentration, while the withering rate of the leaves of S. canadensis surpassed 50% level with 1.8mL/L glyphosate concentration. Compared with the plants grown in monoculture, S. canadensis grown in mixture tended to have higher cumulative height and fewer withered leaves, while I. cylindrica grown in mixed culture grew better after herbicide treatments. There were no significant differences between different planting systems during the experimental period. Planting pattern had obvious impact on the tiller number of I. cylindrica (P < 0.05). (2) Glyphosate significantly weakened the net photosynthetic rate (P_n), stomatal conductance (G_s), and transpiration rate (T_r) of S. canadensis and I. cylindrica (P < 0.05); the latter declined at a higher rate. The responses of intercellular CO₂ concentration (C_i) to glyphosate treatment differed between these two species. C_i of S. canadensis grown in monoculture first reduced and then increased, while C_i of S. canadensis grown in mixture decreased unceasingly; C_i of I. cylindrica grown both in monoculture and mixture increased with increasing glyphosate concentration. (3) Specifically, the maximum net photosynthetic rate (P_nmax) and light saturation point (LSP) of S. canadensis and I. cylindrica declined, while their light compensation point (LCP) increased with increasing glyphosate concentration; glyphosate had no obvious effect on dark respiration rate (R_d) of these two species and the apparent quantum yield (AQY) of S. canadensis, but showed obvious influence on AQY of I. cylindrica (P < 0.05). Planting system had significant effects on the P_nmax and LSP of S. canadensis and I. cylindrica, as well as on the R_d and AQY of I. cylindrica. Glyphosate concentration of 0.6mL/L had less effect on the P_nmax of plants grown in monoculture than those grown in mixed culture, while the effect of glyphosate on the P_nmax of both species grown in different planting systems became similar with increasing treatment concentration. Compared with the native plant I. cylindrica, the alien species S. canadensis had stronger photosynthesis and higher growth rate; glyphosate significantly weakened the photosynthesis of these two species, with I. cylindrica showing greater sensitivity to glyphosate treatment.