PHOTOSYNTHETIC CHARACTERISTICS AND NUTRIENT ABSORPTIN OF SKELETONEMA COSTATUM AT DIFFERENT NITROGEN AND PHOSPHORUS LEVELS

The uptake of nitrogen and phosphorus by Skeletonema costatum, and growth and photosynthesis characteristics of the alga were studied in laboratory batch cultures. The results indicated that the specific growth rate (ranging between 1.51～1.60 d -1) did not vary very much with different nitrate and phosphate concentrations in our experiment, while it was a little higher at low nitrate level; the maximum yield was much lower at middle nitrate and low phosphate level, which decreased by 27% and 41%, respectively compared with low nitrate and high nitrate, and by 64% and 65% compared with middle phosphate and high phosphate. The cells cultured at lower nutrient level showed lower cell-specific light-saturated photosynthetic rate (P cell m) and apparent photosynthetic efficiency (α cell). The cells grown in low nitrate or low phosphate medium were more active and their chlorophyll a-specific light-saturated photosynthetic rate (P chl a m) and apparent photosynthetic efficiency (α chl a) were comparable with those of the cells grown at high nitrate or high phosphate, which was probably the reason that the differences in specific growth rates under all conditions were not obvious. The ratios of uptake rates of nitrate and phosphate by Skeletonema costatum ranged between 0.8～2.6. Fig 3, Tab 4, Ref 17