Effect of Phosphorus on the Photosynthesis and Growth of Sweet Sorghum Seedlings under Salt Stress

Seedlings of sweet sorghum grown under 0% or 0.6% NaCl were treated with 0.1 mmol L-1, 0.2 mmol L-1, 0.6 mmol L-1 and 1 mmol L-1 phosphorus levels respectively. Then the growth parameters such as fresh weight and dry weight, as well as the photosynthetic gas exchange and leaf chlorophyll a fluorescence were determined. Results showed that with the increase of phosphorus level, the fresh and dry weight, net photosynthetic rate (Pn), transpiration rate (Tr), the photochemical efficiency (Phi PSII) and photochemical quenching (qP) of PSII all increased. The sweet sorghum grew better under high phosphorus levels (1 mmol L-1) than under others, implying phosphorus can increase the growth and light utilization ability under both saline and non-saline conditions. Ion distribution analysis indicated sweet sorghum mainly retains sodium in the root, while phosphorus has little effect on the ion distribution in sweet sorghum under both conditions.