Effects of Water Stress on Photosynthetic Characteristics of Cassava Seedlings

The seedling photosynthetic characteristics of two cassava cultivars South China 205(SC205)and South China 8(SC8)under water stress were studied by pot experiment.Three water level treatments were designed:normal supply,mild stress and severe stress.The results showed that under water stress condition,the maximum net photosynthetic rate(Pmax),apparent quantum yield(AQY)and light saturation point(LSP)of SC8 were significantly higher or not lower than that of SC205.The light compensation point(LCP)was not significantly different between the two species.With the severity of drought stress,Pmax,AQY,and LSP decreased,but LCP increased;When PAR was raised from 0 to 2 000 μmol/(m2.s),net photosynthetic rate(Pn),transpiration rate(Tr)and stomatal conductance(Gs)of the two cassava cultivar leaves increased rapidly at the beginning,then intercellular CO2(Ci) decreased rapidly,and consequently all of them changed gently.The water use efficiency(WUE)increased initially and then decreased,indicating that the decline of Pn was considered as a result of stomata restriction under water stress.In conclusion,the photosynthetic characteristics of the two cultivars were generally inhibited under water stress condition.The photosynthetic characteristics and drought resistance of SC8 were better than that of SC205 when water stress existing.