A solution culture was conducted to study the effect of calcium and silicon on root length,photosynthesis and chlorophyll fluorescence in leaves of buckwheat under aluminum stress.Exposure to 0.5 mmol/L and 5 mmol/L Al3 for 15 d inhibited root growth and decreased chlorophyll contents,Pn and Ci,but had no significant difference to Fv/Fm and Fv/Fo.All the parameters aggravated after 30 d.Application of calcium or silicon ameliorated the toxic effects of Al3 on root growth and chlorophyll contents,and caused an increase in Pn and Ci.The addition of silicon to the 0.5 mmol/L and 5 mmol/L Al3 culture increased chlorophyll fluorescence,but changes were not observed in calcium.This suggested that the ameliorating effect of silicon on aluminum toxicity was better than that of calcium.