A Lab Notebook

 
Engel et al. 2004
Engel et al. [2004] cite Obernosterer & Herndl [1995] as having showed that exopolymers released under phosphate limitation are somewhat resistant to bacterial degradation. Engel et al. [2004] comment that other types of nutrient limitiation induced exudates may be recalcitrant to bacterial degradation.
Maranon et al [2004] found that about 20% (compared to the work of Baines and Pace [1991] which estimated 13%) of photosynthate is released as dissolved organic carbon (DOC). They found a decrease in DOC production at night, and an increase in production by healthy populations at suboptimal irradiances. They feel that the traditional perspective of DOC production as an overflow valve for photosynthesis is incorrect. Indeed they interpret their results to show that passive DOC release is a normal physiological mechanism of healthy cells under suboptimal irradiance levels.
Note: glass fiber filters adsob significant amounts of DOC and should not be used for measurements. Maranon et al.'s proposed mechanism for a low irradiance increase in DOC production is the incorporation of inter-cellular C into small molecular weight metabolites due to an irradiance induced slowdown of macromolecular synthesis. Find Raven (1986) which discusses mechanisms of normal cell leakage or exudation. Maranon et al. [2004] conclude that there is no adaptive benefit to enhanced exudation under sub-optimal irradiances, rather it "reflects the inability of the cells to keep all the recent photosynthate within the intracelllular mechanism."
- posted by alex @ 00:41