Abstract: This papor gives a review of allelopathy studied of some imporiant weeds includ Ambrosia artemisiifolia,A. trifida,A. psilostachiya DC. and other species of Ambrosia genus, All these weeds play an imporiant role in the succession of natural vegetation. Meanwhile, an outline of their chemical components and main allelochemicals is also presented in the paper.

Key words: drought, elevated CO₂ concentration, photosynthetic characteristics,  Bothriochloa ischaemum.