Photosynthetic properties of different sugar beet genotypes under phosphorus deficiency

stomatal conductance, transpiration rate, intercellular CO2 concentration, transpiration rate and photosynthetic rate of the individual cultivar are completely in accord with the resistant ability of the respective cultivar, i.e. cv.20 cv.17 cv.14. Three different sugar beet genotypes (Beta vulgaris L. cv.14 (diplont), cv.17(tetraplont), cv.20(triplont)) screened in a former research with different resistant abilities to P deficiency were used to investigate the effects of long term phosphorus stress(P 1mol/kg) on photosynthetic properties of the individual attached leaves by the methods of sand culture in growth chambers and outdoor natural condition respectively. The results show that contents of Pi and chlorophyll are decreased significantly (P0.05) under the long term phosphorus stress, the decreased rates of the two properties of the genotype cv.20 are obviously （P0.05）smaller than those of cv.14. P deficiency has a significant negative effect on stomatal conductance and transpiration rate. Effects of P stress on intercellular CO2 concentration vary with the cultivars, significant decrease for cv.14, little change for cv.17, and significant increase for cv.20. To compare with the treatment of P 100 mol/kg, photosynthetic rates of the three cultivars under the P stress are significantly decreased, the decreases are cultivar dependent, of them cv.14 is the largest, cv.17 is in the middle, cv.20 is the smallest, and the difference of photosynthetic rates between the cultivars are also significant. Effects of the P stress on photosynthetic rate varies with the growth environments, the resistant index under the growth chamber environment is larger than that under the outdoor condition. Under the conditions of P deficiency, the magnitude of resistant indices concerning the characteristics of P content of beet plant,stomatal conductance, transpiration rate, intercellular CO2 concentration, transpiration rate and photosynthetic rate of the individual cultivar are completely in accord with the resistant ability of the respective cultivar, i.e. cv.20 cv.17 cv.14.