Abstract: We comparatively studied the changes of the gas exchange parameters including the maximum net photosynthetic rate(P_max), light saturation point(LSP), dark respiratory rate(R_d), potential maximum photosynthetic rate(A_max), light photorespiration(R_P), the maximum carboxylation rate of rubisco(V_cmax), the maximum rate of RuBP regeneration(J_max) and the contents of photosynthetic pigments of invasive Bidens frondosa and its native associated Lactuca indica to the drought stress including light drought stress(LD), moderate drought stress(MD), severe drought stress(SD) and normal irrigation(CK) in a greenhouse pot experiment. The variation trends of different parameters of two plants were in substantial agreement, however the changing amplitude for invasive B.frondosa was significantly lower than that for its associated L.indica, and even the aboveground part of L.indica died and couldn't recover after rehydration under severe drought stress. Under drought stress, the main reason of the photosynthesis decrease was stomata limitation for B.frondosa, but non-stomata limitation for L.indica. Compared with L.indica, B.frondosa had higher respiration efficiency(RE), which was helpful for more accumulation of photosynthetic products, the higher light photorespiration(R_P) could protect photosynthetic apparatus from harm, and it could hold higher abilities of photochemical reaction and carboxylation rate of RuBP under drought stress, maintaining higher photosynthetic ability. The responding trends of invasive B.frondosa and its native associated L.indica were in substantial agreement, but B.frondosa had stronger extreme drought tolerance ability and watering revovery ability with better adaptation to drought, which would be helpful for its invasion.

Key words: invasive species, Bidens frondosa, drought stress, photosynthetic characteristics, invasiveness