Differential response of fatty acid composition in the different lipid classes from particulate matter in a high arctic fjord (Kongsfjorden, Svalbard)

Abstract

Lipid classes and the respective fatty acid composition of natural particulate matter were studied on a seasonal basis in the Arctic fjord Kongsfjorden (Svalbard) during the early summer of 2006 and the spring, summer of 2007. Polar lipids were the major lipid class most of the times in 2006 and at all times in 2007. Among neutral lipids triglycerides were dominant. Polar lipids were divided into glycolipids (chloroplast membranes) and phospholipids (live cell membranes). Glycolipids were further divided into monogalactosyldiglycerides (MGDG), the major glycolipid, followed by digalactosyldiglycerides (DGDG) and Sulfoquinovosyldiglycerides (SQDG). In 2007, changes in both polar lipid constituents showed similar increasing trend from May to mid June but subsequently showed opposite trends from July to September. The seasonal pattern of particulate glycolipids was one of the low concentrations of MGDG in June followed by an increase between late June and September. SQDG exhibited a similar trend while DGDG displayed an opposing trend. In 2007, fatty acid composition of phospholipids, glycolipids and neutral lipids was dominated by saturated acids at all times followed by mono unsaturated acids and polyunsaturated acids with docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and 18:5n-3 as major contributors. Glycolipid fatty acid pattern differed from that of phospholipids, showing a more important contribution of 18:5n-3. Neutral lipid composition differed from the other two classes by a larger contribution of 16:1n-5 and percentages of EPA, DHA, 18:5 and 18:4n-3 lower than in the two structural classes. Factorial correspondence analysis (FCA) of the fatty acid composition of all classes illustrated a seasonal transition in species composition and/or physiological states for the phospholipids and the different processes of chloroplast membrane adaptation in relation to taxonomic changes for the glycolipids. Neutral lipid changes were more complex because of the combined influence of growth rates, nutrient limitations and community shifts. The differential response of the different lipid classes is discussed in relation with the complex interactions between community structure, environmental adaptation and metabolic processes.