Effect of different temperature fluctuations and different initial concentrations of NO₃-N and PO₄-P on growth, nutrient uptake and photosynthetic efficiency of <i>Gracilaria asiatica</i>

Abstract

The effects of three temperature fluctuations combined with different initial NO₃-N and PO₄-P concentrations on growth rate, nutrient uptake as well as photosynthetic efficiency were assessed. <i>Gracilaria</i> <i>asiatica</i> were collected from the coast of Fujian, China for this present study. Study revealed that after 15 days, the highest growth rate of <i>G. asiatica</i> was recorded at 20ºC under low initial nutrient concentration whiles the lowest was recorded at 25ºC under high initial nutrient concentration. The NO₃-N uptake rate of <i>G. asiatica</i> under low and high initial concentration at temperatures 20ºC and 20±2ºC were higher than other conditions after 15 days. On the other hand the PO₃-P uptake rate under high initial concentration at temperatures 20ºC and 20±2ºC were lower than other conditions after 15 days. After the third day, NO₃-N and PO₄-P were exhausted from the medium when the initial concentration were low under different temperature fluctuations. Photosynthetic efficiency observed at temperatures 15ºC and 15±2ºC decreased from beginning whiles the photosynthetic efficiency at 25ºC and 25±2ºC increased from beginning. We concluded that temperature fluctuations integrated with different initial NO₃-N and PO₄-P concentrations affects growth rate, nutrient uptake as well as photosynthetic efficiency of <i>G.</i> <i>asiatica</i>.