Leaf gas exchange and photosynthetic light-response curves of cassava genotypes under drought stress during the early growth stage and after recovery.

Abstract

This study aimed to gain insights into the photosynthesis capacity and genotypic differences in response to drought imposed at an early growth stage of cassava. Leaf water potential (LWP), leaf gas exchange, and photosynthetic light-response curves were investigated in six field-grown cassava genotypes under full irrigation and drought imposed for 60 d during 3-5 months after planting. During the drought period, mean LWP at predawn (LWP_pre) was significantly lower than that in the control plants, while the mean midday LWP (LWP_mid) was similar. During the drought period, the mean stomatal conductance was reduced from 0.36 to 0.09 mol(H₂O) m^-2 s^-1, mean transpiration rate from 5.30 to 1.86 mmol(H₂O) m^-2 s^-1 with the concomitant reduction in net photosynthetic rate (P _N) from 27.45 to 16.34 μmol(CO₂) m^-2 s^-1. Analysis of the light-response curves revealed a reduction in the light-saturation point (I _sat), the light-saturated net photosynthetic rate (P _Nmax), and the apparent quantum yield (AQY). After rewatering for 30 d, the drought plants could fully recover. In conclusion, P _N at high light intensity, P _Nmax, I _sat, and AQY were useful parameters to differentiate genotypes for variability in drought tolerance.