The effects of temperature and nutrient concentrations on nitrate and phosphate uptake in different species of Porphyra from Long Island Sound (USA)

Abstract

Uptake rates of nitrate and phosphate were measured for four species and one variety of Porphyra from Long Island Sound (USA) at two temperatures and two nutrient medium concentrations at increasing intervals over a 24- or 48-h period. Maximum uptake rates found were: V 30 μM 0–1 h=73.8 μmol NO 3 g −1 DW h −1 and V 3 μM 0–1 h=16.7 μmol PO 4 g −1 DW h −1, in the two thinnest Porphyra. We found that the nitrate uptake rates were significantly greater at 30 μM than 3 μM NO 3 concentration, and that the uptake rates decreased with time of exposure. Temperature (5, 15, and 25 °C) did not have as strong an effect on nitrate uptake rates as did nutrient concentration. Q 10 values and uptake rates at four different nitrate concentrations indicated that nutrient uptake at 5 °C was initially an active process. After 24 h, the processes involved appeared passive as Q 10 values were between 1.0 and 1.3 and nitrate uptake curves were linear. Nitrate uptake rates correlated positively with the surface area/volume (SA/V) ratio. No coherent trends were found for uptake of phosphate, except that the uptake rates were significantly higher in 30 μM NO 3 medium as opposed to 3 μM NO 3. We did not find any significant difference in uptake rate and pattern between the summer species Porphyra purpurea (Roth.) C. Agardh, the eurythermic Porphyra suborbiculata Kjellm., the winter species Porphyra rosengurttii J. Coll and J. Cox, and the two varieties of Porphyra leucosticta Thur. Le Jol. (both winter species).