Abstract:Soil pot culture and solution culture were conducted to study the effects of arsenic stress on plant growth,arsenic uptake and bioaccumulation,arsenic speciation in roots and leaves,and organic acids in root exudates of cowpea（Vigna unguiculata L.）and tomato（Cyphomandra betacea L.）.The results showed that there was significant difference in arsenic tolerance response between cowpea and tomato.Cowpea was regarded as the As-sensitivity with the characterization of the significant reduction of biomass and yield under As stress with decrease of 47% and 54% respectively compared with the controls.In contrast,tomato was selected as the As-tolerance,featuring as the significant increasing of biomass and yield under arsenic stress to 1.56 times and 1.51 times,respectively.The As concentration in fruit of cowpea (0.019 7 mg/kg FW) was higher than that in tomato (0.008 5 mg/kg FW),but they didn’t exceed the National Food Safety Standards (0.05 mg/kg FW).Arsenic in cowpea and tomato existed as inorganic speciation (arsenate and arsenite),and more than 65% arsenic in leaves and 95% in roots were arsenite.Though there was no significant difference between arsenic speciation in roots of cowpea and tomato,the percentage of arsenate in leaves of cowpea were greatly higher than that of tomato.Arsenic stress significantly increased quantities of malic acid and acetic acid in root exudates of two vegetables.Compared with cowpea,tomato can exuded more organic acids under arsenic stress.