The effect of light and temperature on DOC excretion by phytoplankton

Abstract

The separate effects of light intensity (O-3,000 pmol quanta m-2 s-l) and temperature (5"-45"C) on excretion of dissolved organic carbon (DOC) by three phytoplankton species were examined under controlled laboratory conditions in axenic cultures. Ours is the first comparative study of the effects of a wide temperature and irradiance range on DOC excretion by different species of phytoplankton under identical conditions. Tight coupling was found between the rates of carbon fixation and of absolute DOC excretion over a wide range of h-radiances (O-l,500 pmol quanta m-2 s-l) in all three species with excretion ranging from 1 to 55% of production. Chlorda vulgaris and Synechococcus sp. showed parallel temperature-dependent changes in photosynthesis and of absolute DOC excretion (5"-45"C); in Isochrysis galbana absolute excretion was temperatureindependent, but photosynthesis was temperature-dependent. In all cases, increased excretion percentages were found under extreme irradiances and temperatures that depressed photosynthesis. In general, we suggest that high fluxes of DOC toward bacterial food chains may be expected only under conditions favorable for photosynthesis, although the percentage of DOC excretion is then low.

Size-fractionated dissolved primary production and carbohydrate composition of the coccolithophore <i>Emiliania huxleyi</i>

“…Cell normalized production of PO 14 C was on average ∼ 0.33 pmol C cell −1 d −1 and well within the range of published values (0.12-0.64 pmol C cell −1 d −1 ; Biddanda and Benner, 1997;Borchard and Engel, 2012). The partitioning of organic carbon between dissolved and particulate pool was shown earlier to be highly influenced by environmental conditions such as light, temperature and nutrient supply (Myklestad and Haug, 1972;Zlotnik and Dubinsky, 1989;Staats et al, 2000;Wetz and Wheeler, 2007). Nutrient depletion, however, seems to be the major factor leading to excess DOC excretion from algae cells to the surrounding environment and was reported from a variety of field and lab experiments (Fogg, 1983;Wood and VanValen, 1990;Smith and Underwood, 2000;Lopez Sandoval, 2010.…”

“…In accordance with the overflow model, data from coastal, marine and estuarine systems revealed a linear relationship between PP and ER, and factors influencing PP were suggested to also affect ER (Baines and Pace, 1991). Such effects were shown for light (Zlotnik and Dubinsky, 1989) and later also suggested for CO 2 (Engel, 2002) and temperature (Moran et al, 2006). Under nutrient limitation, however, substantial ER was observed when PP was reduced, leading to higher percentage of extracellular release (PER) (Myklestad et al, 1989;Goldman et al, 1992;Obernosterer and Herndl, 1995;Halewood et al, 2012).…”

CO<sub>2</sub> increases <sup>14</sup>C primary production in an Arctic plankton community

“…The extracellular release of DOC is a normal function of algal cells (Fogg, 1966) and represents with ∼ 3-40 % (percentage of extracellular release, PER) a significant fraction of primary production (Myklestad, 1977;Mague et al, 1980;Baines and Pace, 1991). Factors influencing primary production, such as light and temperature, were shown to also affect the production of DOC (Zlotnik and Dubinsky, 1989;Baines and Pace, 1991;Engel et al, 2011).…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…Like passive diffusion, the loss of DOM from photosynthetic overflow is generally regarded as a consequence of inefficiencies in cell physiology with the extracellular products serving no function outside the cells. The release of photosynthate under conditions of high light (Hellebust, 1965;Zlotnik & Dubinsky, 1989) and nutrient scarcity may be an overflow mechanism when photosynthesis occurs more rapidly than is required for growth (Fogg, 1983;Wood & Van Valen, 1990). For example, if a cell is growing under conditions of nitrogen limitation there will be insufficient nitrogen to support growth of the cell, which requires the synthesis of proteins, nucleic acids and other nitrogen-containing compounds.…”