Effect of Phosphate Limitation on Photosynthetic Physiology of the Coccolithophore Emiliania huxleyi
Coccolithophores are one of the most important calcified phytoplankton,playing a key role in the marine carbon cycle.The growth and photosynthesis of coccolithophores are affected by nutrient availability.Cell concentration,cellular pigment content,and photosynthetic activity of Emiliani huxleyi,a model coccolithophore species,were investigated during the exponential growth phase under high phosphate concentration,the stationary growth phase under low phosphate concen-tration,and the decline growth phase under phosphate-free conditions.The results show that the growth rate,cellular chlorophyll a content,photochemical efficiency,and the functional absorption cross-section of photosystem Ⅱ decreased with decreasing phosphate availability.The average time for electron transport from the initial electron acceptor to the plastoquinone pool increased with decreasing phosphate availability.When cells under phosphate-free conditions were inoculated into high phosphate concentration,and cultured for 4 days,growth rate,cellular pigment content,and photosynthetic activity of E.huxleyi were restored to levels close to those under high phosphate conditions.These results indicate that E.huxleyi cells can rapidly respond to fluctuations in phosphate availability and adjust their growth and photosynthetic function,which is one of the reasons for E.huxleyi's competitive advantages in phosphate-limited environments.
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