Flexible C : N ratio enhances metabolism of large phytoplankton when resource supply is intermittent

[摘要] Phytoplankton cell size influences particle sinking rate, food webinteractions and biogeographical distributions. We present a modelin which the uptake, storage and assimilation of nitrogen and carbonare explicitly resolved in different-sized phytoplankton cells. Inthe model, metabolism and cellular C : N ratio are influenced bythe accumulation of carbon polymers such as carbohydrate and lipid,which is greatest when cells are nutrient starved, or exposed tohigh light. Allometric relations and empirical data sets are used toconstrain the range of possible C : N, and indicate that larger cellscan accumulate significantly more carbon storage compounds thansmaller cells. When forced with extended periods of darknesscombined with brief exposure to saturating irradiance, the modelpredicts organisms large enough to accumulate significant carbonreserves may on average synthesize protein and other functionalapparatus up to five times faster than smaller organisms. Theadvantage of storage in terms of average daily protein synthesisrate is greatest when modeled organisms were previously nutrientstarved, and carbon storage reservoirs saturated. Small organismsmay therefore be at a disadvantage in terms of average daily growthrate in environments that involve prolonged periods of darkness andintermittent nutrient limitation. We suggest this mechanism isa significant constraint on phytoplankton C : N variability andcell size distribution in different oceanic regimes.

[学科分类] 地球化学与岩石