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General Session 3: Biological oceanography & global change |
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Elemental stoichiometry and nutrient regeneration of Noctiluca scintillans in response to prey of different nutrient quality
GS3-35
Shuwen Zhang, Hong Kong University of Science and Technology
Hongbin Liu* , Hong Kong University of Science and Technology
Patricia M. Glibert, University of Maryland Center for Environmental Science, Horn Point Laboratory
Cui Guo, Hong Kong University of Science and Technology
Ying Ke, Hong Kong University of Science and Technology
Presenter Email: liuhb@ust.hk
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| To study the stoichiometric homeostasis of Noctiluca scintillans and the magnitude of its nutrient regeneration when facing different quality food, N. scintillans cells were allowed to feed 1 d upon the diatom, Thalassiosira weissflogi, which were cultured on nutrient-balanced (f/2), N-limited, and P-limited media, respectively. The elemental stoichiometry and the computational and experimental excretion rates of C, N and P of these different grown cells were subsequently determined. Results showed that cellular elemental ratios of N. scintillans were nearly homeostatic, but the ratio of its intracellular NH4+-N and PO43- -P, which accounted for >32% and >40% of its N and P pools, was weakly regulated. N. scintillans apparently is able to differentially allocate N and P to organic and inorganic pools to maintain overall homeostasis. Nevertheless, its internal N was regulated more strongly and efficiently than that for P, as indicated by its comparatively stable C:N ratio compared to C:P and N:P ratios when the nutrient ratios of its food, and subsequently, its rate of feeding, changed, especially on N-limited prey. Model predictions reveal that rates of C, N and P excretion by actively feeding N. scintillans were highly affected by food quality, and differed from those obtained in the starvation experiment, of which N. scintillans cells previously reared on nutrient-balanced and N-limited prey generally had similar, but higher, excretion rates of C and N than model predication. This partially indicates its higher requirement of C and N for basal maintenance than growth. Nevertheless, both computational and experimental results showed that N. scintillans tends to retain P and preferentially release N, highlighting its vulnerability to P-limitation. In all, N. scintillans has a shifting role in the food web, from mainly exerting top-down control on phytoplankton during most of its pelagic life to fueling bottom-up processes during bloom senescence due to liberation of intracellular nutrients. |
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