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Zusammenfassung:
Laboratory growth experiments were used to test whether observed phosphorus limitation in Daphnia is a direct effect of P availability. Daphnia was fed the algae Cyclotella and Scenedesmus, each P saturated or P limited. The algal species were chosen because of their distinct fatty acid composition, particularly with respect to their eicosapentaenoic acid (20:5-omega-3) content. Although both algal species had reduced 20:5-omega-3 content under P limitation, P-limited Cyclotella had a substantially higher 20:5-omega-3 content than did P-saturated Scenedesmus. In keeping with its P and 20:5-omega-3 content, P-limited Scenedesmus was the lowest quality of food. Inconsistent with mineral P limitation in Daphnia but in agreement with the 20:5-omega-3 content, P-starved Cyclotella was a better quality of food than was P-sufficient Scenedesmus. Thus P limitation seems to be a rather indirect effect of changes in algal biochemical composition in response to nutrient stress
