Hemistepta lyrata,Rumex chalepensis,Vicia Sepium,Chenopodium album,Clinopodium chinense and Sedum album were used to study the effects of"past (150 mumol /mol) -present (400 mumol /mol) -future (700 mumol /mol) "CO_2 concentrations on plants growth in walk-in CO_2 concentration chambers.Results showed that CO_2 concentration enrichment stimulated the total biomass and relative growth rate in all 6 species,but the increasement from the past low to the present CO_2 concentration was greater than that from the current to the future CO_2 concentration.The root mass fractions were all stimulated by increased CO_2 concentration under present level,but not affected by increased CO_2 concentration above present level.These results indicate that plant adaptations to past low [CO_2]might still constrain the growth response to future high [CO_2].These results were contribute to understand the herb responses to climate change in the future,and provide theoretical basises for assessing and predict the physiological and ecological impacts of global climate change on plants.