| In this study we have investigated whether the carbon isotopic signature differs between different groups and species of marine phytoplankton depending on growth phase and nutrient conditions. The 3 investigated algal species, Amphidinium carerae, Prorocentrum micans and Alexandrium tamarense, were grown in batch monocultures and analysed forδ13C andδ15N in both exponential and stationary phase. Our results show that the carbon and nitrogen isotopic signature of phytoplankton may be differ among different phytoplankton species, between exponential and stationary phase, as well as between nutrient treatments.For all the cultured species,δ13C signatures ranged from -25.96‰(Alexandrium tamarense) to-16.14‰(Prorocentrum micans) in the exponential phase and from-25.96‰(Alexandrium tamarense) to-17.02‰(Prorocentrum micans) in the stationary phase.δ15N signatures ranged from -12.08%o (Amphidinium carerae) to 6.86%o (Amphidinium carerae) in the exponential phase and from-11.72%o (Prorocentrum micans) to 6.26%o (Amphidinium carerae) in the stationary phase.Three species were also grown under nutrient sufficient and nitrogen or phosphorus deficient conditions. The best conditions for all the cultured species is C(NO3-)=1.484mmol/L, C(PO43-)=0.128mmol/L and N:P=12. Nitrogen limitation and phosphorus limitation both resulted in a more positiveδ15N signature compared to nutrient sufficient conditions, whereas no clear effect could be observed forδ13C during Nitrogen limitation and phosphorus limitation. However, the most positiveδ13C andδ15N are both observed when N:P=1. For Amphidinium carerae and Prorocentrum micans,δ13C signatures in the exponential phase is more positive than that in the stationary phase. For Amphidinium carerae,δ15N signatures in the exponential phase is more negative than that in the stationary phase, but it is opposite for Prorocentrum micans. And no effect could be observed between exponential and stationary phase for Alexandrium tamarense. |
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