Canopy and Leaf Photosynthetic Characteristics and Water Use Efficiency of Sweet Sorghum under Drought Stress1

摘要

The objective of this paper was to examine the relationship between Water Use Efficiency (WUE) at the canopy and leaf levels, to determine soil moisture conditions, which can optimize yield, and WUE of sweet sorghum, thus providing some theoretical foundation for using marginal land effectively and developing production of sweet sorghum (Sorghum bicolor (Linn.) Moench). Three levels of soil moisture conditions were established, and photosynthetic characteristics and yield were measured. The canopy apparent photosynthetic rate (CAP) and leaf photosynthetic rate (P_N) were reduced gradually with increased drought stress, and the CAP was lower than the P_N under every soil moisture condition. The P_N had a midday depression phenomenon, but the CAP didnot exhibit this midday depression phenomenon under severe drought stress. The linear regression relationship of CAP and P_N was CAP = 1.5945 + 0.1496 P_N. The canopy apparent WUE_C and leaf WUE_L were the highest under moderate drought stress. It was 5.3 and 5.8 times higher than the WUE, in mid-July and late August, respectively. The stem fresh biomass yield was 77 tons/ha under moderate drought stress, and WUE of aboveground biomass yield (WUE_B) was also the highest. Our results show that moderate drought stress did not result in a significant reduction in biomass yield but increased WUE significantly.