REU: The N:P Stoichiometry of Nutrient Release by Daphnia

水生食草动物利用的食物基础的C：N：P比率可能有很大的差异。动物调整它们对N和P的同化，以便更有效地吸收供应较少的元素。这项关于放牧、同化和释放营养物质的化学计量学的假设预测，食草动物使营养限制模式发生变化，导致它们的藻类猎物从N和P的共同限制转向N或P的限制。质量平衡技术将允许摄取，同时测定了不同C：N：P藻类对不同浓度藻类的N、P同化和再释放，并测定了在不同C：N：P藻类上养殖的水蚤组织C：N：P。该项目将确定N和P的循环效率，以及养分浓度比率是否与通常假设的供应比率有关。此外，它还将探索水生生态系统中食物网动态的基本后果，同时提供关于主要水生生物氮和磷生理学的迫切需要的基本数据。

Aquatic herbivores utilize a food base that can vary widely in its C:N:P ratio. The animals adjust their assimilation of N and P so that the element in shorter supply is assimilated more efficiently. The hypothesis of this proposal on the stoichiometry of grazing, assimilation and release of nutrient predicts that grazers make nutrient limitation patterns diverge, leading their algal prey away from co-limitation by N and P and toward limitation by either N or P. A Mass balance technique will allow ingestion, assimilation and re-release of N and P to be measured simultaneously for Daphnia faced with different concentrations of algae of differing C:N:P. Determinations of tissue C:N:P of Daphnia that have been reared on algae of different C:N:P will also be performed. This project will determine the recycling efficiencies of N and P and whether nutrient concentration ratios are related to supply ratios, as is commonly assumed. Also, it will explore fundamental consequences of food web dynamics in aquatic ecosystems while providing badly needed basic data on the N and P physiology of a major aquatic organism.