Water- and Nitrogen-use Efficiencies of Sweet Sorghum Seedlings are Improved under Water Stress

The physiological mechanism underlying the high productivity of sweet sorghum (Sorghum bicolor (L.) Moench) under drought is not well understood. Water and nitrogen utilization features of leaves can play key roles in plant drought tolerance. The objective of this study was to investigate the water and nitrogen utilization of sweet sorghum seedlings under prolonged water stress within controlled environmental conditions. Under prolonged water stress, leaf area and total water loss per plant decreased significantly, leaf dry mass per unit area increased but the dry mass of the whole plant was unaffected. Total leaf nitrogen, leaf nitrogen per unit area and leaf nitrogen concentration of stressed plants decreased significantly, indicating a reduced accumulation of leaf nitrogen. The photosynthetic rate of stressed plants recovered completely three days after water stress treatment, while transpiration rate was consistently lower than the controls, resulting in improved instantaneous water-use efficiency (WUE). Photosynthetic nitrogen-use efficiency (PNUE) increased significantly, which may contribute to the increase in biomass based nitrogen-use efficiency and WUE correlated positively with PNUE. In conclusion, improved water-and nitrogen-use efficiencies under water stress may both contribute to the high degree of physiological acclimation of sweet sorghum to drought. (C) 2014 Friends Science Publishers