Abstract: Taking alfalfa (Medicago sativa) cv.Golden Empress (drought-resistance) and cv.Sanditi (drought-sensitivity) as target materials,we set four treatments including normal water supply (CK),light drought stress (LS),middle drought stress (MS) and severe drought stress (SS) treatments to investigate the responses of photosynthetic characters (including photosynthetic rate,chlorophyll content and fluorescence parameters) of different alfalfa to drought at initial bloom stage.The results suggested that drought reduced the net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate but increased stomatal limitation value,and water use efficiency increased and then decreased at two alfalfa,while cv.Golden Empress had a smaller decreasing magnitude in photosynthetic rate comparing with that of cv.Sanditi.Light drought enhanced the content of chlorophylla,chlorophyll(a+b) and chlorophylla/b but middle drought and severe drought both hampered their increases.Drought also significantly increased the minimal fluorescence (Fo) but made actual photochemical efficiency of PSⅡin the light (φPSⅡ),electron transport rate (ETR) and maximal photochemical efficiency of PSⅡ (Fv/Fm) decreased.However,light drought increased the potential activity of PSⅡ (Fv/Fo) but middle and severe drought showed an inverse trend.Drought obviously reduced the aboveground biomass when the drought occurred but made little effect on the aboveground biomass except a slight increase under light drought.The decrease of Pn was primarily contributed by the stomatal restriction,while alfalfa exhibited obvious stress responses under slight drought,which kept it having a high Pn.In conclusion,the response of cv.Golden Empress to drought was mild,which indicated a high drought tolerance.

Key words: Drought stress, Alfalfa, Photosynthesis, Fluorescence parameters, Aboveground biomass

CLC Number: 

• S551.01