Sources of Regenerated Nitrogen

Nitrogen release from phytoplankton can occur two ways. First is direct release, which includes active release, often termed exudation, or passive difiusion from the cell (Fo, 1983). The second is mediated release, where the release occurs when phytoplankton 

The magnitude of direct release has been a topic of much debate (Bronk and Ward, 2000 Bronk et al., 1994 Slawyk et al, 1998 Slawyk et al, 2000). A similar debate took place around DOC release in the 1960s and 1970s (Sharp, 1977). Cultures are the tool of choice for the study of direct release because they remove the effect of other trophic levels, such as grazing or, under axenic conditions, bacteria (reviewed in Antia et al, 1991 Bronk and Flynn, 2006). Nitrogen release has been studied extensively in culture and there is abundant Hterature on uptake and release, particularly of DON, from work done in the 1950s—1970s (reviewed in Antia 

When considering release under N-limited conditions it is important to remember that the commonly measured DON release rates are net rates such that reincorporation of recently released DON would result in an underestimate of the true DON release rate. Many phytoplankters can use organic N to fulfill their nutritional requirements such that reincorporation is ftkely, particularly under N-limiting conditions (reviewed in Bronk et al., 2007). An example of this was seen in a culture study with Alexandrium catenella where DON release was observed early in the 

Culture Substrate Released Gross N uptake (%) Method Reference 

Percent release equals release divided by uptake + DCAA release + DFAA release the uptake rate was calculated as the increase in algal N over the first day. 

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Sources of regenerated nitrogen associated with sediments... 

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