Exudates phytoplankton

Sell, A. F., and J. Overbeck. 1992. Exudates Phytoplankton-bacterioplankton interactions in Plussee. Journal of Plankton Research 14 1199-1215. 

Smith RC, Prezelin BB, Baker KS, Bidigare RR, Boucher NP, Coley T, Karentz D, MacIntyre S, Matlick HA, Menzies D, Ondrusek M, Wan Z, Waters KJ (1992) Ozone depletion ultraviolet radiation and phytoplankton biology in Antarctic waters. Science 255 952-959 Sommaruga R, Psenner R (1997) Ultraviolet radiation in a high mountain lake of the Austrian Alps air and underwater measurements. Photochem Photobiol 65 957-963 Swanson AK, Druehl LD (2002) Induction, exudation and the UV protective role of kelp phlorotannins. Aquat Bot 73 241-253... 

DOM is also released into seawater by phytoplankton fiar reasons that are as yet imclear. On average, 13% of the phytoplankton carbon is released as exudates, some of which are low-molecular-weight compounds, such as free amino acids and tricarboxylic acids. Other exudates are high-molecular-weight compoimds, such as the acylated heteropolysaccharides. These macromolecules are relatively chemically resistant and appear to form a large portion of the HMW DOC pool. 

Release rates of exudates from phytoplankton range from 0 to 80% of carbon fixed. These rates are dependent on species composition, physiological state, nutrient deficiency, temperature, and Ught limitation. Some evidence suggests that exudation is a mechanism for release of excess organic matter from cells when nutrient availability is too low to enable their usage as metabolic fuel. 

Serritti, A., Pellegrini, D., Barhigiani, C. and Ferrara, R., 1985. Copper complexing capacity of phytoplanktonic cell exudates. Mar. Chem. (submitted). 

An alternative approach for screening the composition of phytoplankton exudates is to use either 14C-tracer methods combined with chemical fractionation (Hama and Handa, 1987 Siuda and Wcisko, 1990 Sundh, 1991) or colorimetric methods (Obernosterer and Herndl, 1995 Biddanda and Benner, 1997) to characterize the contribution of different classes of organic compounds (carbohydrates and amino acids in polymeric or monomeric forms) to the total pool of exudates. These studies revealed that monomeric and combined carbohydrates were the major components of exudates, typically accounting for 20-90% of the total extracellularly released DOM. 

The most commonly used approach to quantify the concurrent flux of algal exudates to heterotrophic bacteria is to combine the 14C-tracer method with a differential filtration step in which free-living bacteria are physically separated from phytoplankton and excreted DOM (reviewed by Baines and Pace, 1991). The data presented in this review indicate that, on average, 46% of the excreted DOM is incorporated by bacteria. One limitation of this approach is that bacteria attached to particles are largely excluded from the analysis, but this can, to some extent, be overcome by monitoring the distribution of heterotrophic bacteria in both size fractions (Sondergaard et al., 1985). 

Larsson, U., and A. Hagstrom. 1982. Fractionated phytoplankton primary production, exudate release and bacterial production in a Baltic eutrophication gradient. Marine Biology 67 57-70. 

Murray, A. G. 1995. Phytoplankton exudation Exploitation of the microbial loop as a defense against algal viruses. Journal of Plankton Research 17 1079-1094. 

Petit, M., G. P. Alves, and P. Lavandier. 1999. Phytoplankton exudation, bacterial reassimilation and production for three diel cycles in different trophic conditions. Archiv fiir Hydrobiologie 146 285-309. 

As mentioned earlier, the abundance of carbohydrates in ocean DOM relative to river DOM does not reflect the biochemical compositions of terrestrial plants and marine phytoplankton. It appears that carbohydrates in plant litter are largely degraded in soils, resulting in relatively low concentrations in river DOM. Carbohydrates are the major components of exudates from phytoplankton (Biddanda and Benner, 1997 Biersmith and Benner, 1998), and herbivorous grazing also releases carbohydrates to the DOM reservoir (Strom et al., 1997). The in situ production of dissolved carbohydrates in the surface ocean appears to result in a greater relative abundance of carbohydrates in the ocean relative to rivers. 

Bjornsen, P. K. 1988. Phytoplankton exudation of organic matter Why do healthy cells do it Limnology and Oceanography 33 151-154. 

Spatial variability in the abundance of phytoplankton exudates, uptake of DOM by bacteria, chemical removal processes (e.g., flocculation, deflocculation, adsorption, aggregation, precipitation), inputs from porewaters during resuspension events, and atmospheric inputs can all contribute to nonconservative behavior in estuaries. 

Kwint RLJ, Kramer KJM (1996) The annual cycle of the production and fate of DMS and DMSP in a marine coastal system. Mar Ecol Prog Ser 134 217-224 Laroche D, Vezina AF, Levasseur M, Gosselin M, Stefels J, Keller MD, Matrai PA, Kwint RLJ (1999) DMSP synthesis and exudation in phytoplankton a modeling approach. Mar Ecol Prog Ser 180 37 19 Lee PA, de Mora SJ (1999a) A review of dimethylsulfoxide in aquatic environments. Atmosphere-Ocean 37 439-456... 

Dutz J, Klein Breteler WCM, Kramer G (2005) Inhibition of copepod feeding by exudates and transparent exop-lymer particles (TEP) derived from a Phaeocystis globosa dominated phytoplankton community. Harmful Algae 4 929-940... 

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... 

Larsson, U., and Hagstrom, A. (1979). Phytoplankton exudate release as an energy source for the growth of pelagic bacteria. Mar. Biol. 52, 199—206. 

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