Microalgae are rich sources of vitamins, pigments such as ?-carotene and other food and drug metabolites that are important for biological researchers in recent years. They are also very important as live food for zooplankton, mollusca and larvae. Since the environmental factors affect on the growth, production and biochemical compositions in microalgae, therefore, the combined effects of temperature and photoperiod on the growth, biomass, chlorophyll, carotenoids and ascorbic acid of freshwater microalgae Scenedesmus quadricauda were investigated. The experiment was carried out as completely randomized design at three photoperiods (8L:16D, 12L:12D and 16L:8D) and three temperatures (20, 25 and 30 ° C) for 20 days. Results showed that the increasing of photoperiod and temperature was significantly (p?0.05) increased density, specific growth rate and the biomass. The maximum densities were 9.88×10 6 ±49301 (mean±SE), 1.22×10 7 ±805191 and 1.32×10 7 ±929269 cells/ml in combination of 8L:16D light/dark at 20, 25 and 30 ° C, respectively. However, the maximum densities in 12L:12D light/dark photoperiod at 20, 25 and 30 ° C were 1.34×10 7 ±219848, 1.46×10 7 ±186339 and 1.75×10 7 ±237317 cells/ml, respectively. The densities of 2.02×10 7 ±116369, 1.91×10 7 ±278436 and 2.11×10 7 ±843439 cells/ml were obtained at 16L:8D light/dark photoperiod and 20, 25 and 30 ° C, respectively . In addition, the mean specific growth rate and doubling time were ranged 0.15-0.37 /day and 1.86-4.47 days, respectively. Maximum chlorophyll a and tatal carotenoids were 16.52±0.06 and 6.32±0.055 mg/l, respectively, at 16L:8D and 30 ° C.The maximum biomass and chlorophyll b were 0.47±0.028 mg/ml and 10.69±0.78 mg/l, respectively, at 16L:8D and 25 ° C. The highest acid ascorbic content at 12L:12D light/dark photoperiod at 20, 25 and 30 ° C were 34.9±4.4, 38.2±6.5 and 33.3±6.7 fg/cell, respectively. The acid ascorbic content of 56.8±11.7, 54.6±7.4 and 60.6±10.1 fg/cell were obtained at 16L:18D light/dark photoperiod and 20, 25 and 30 ° C, respectively. The results indicated that increasing photoperiod and temperature in the cultivation of microalgae S. quadricauda improve growth, biomass and ascorbic acid content. Key words: photoperiod, temperature, Scenedesmus quadricauda , ascorbic acid, biomass, growth
