Formation of Dissolved Free Amino Acids in Seawater and Its Coupling to Uptake

Fuhrman博士的更新建议是扩展对溶解的游离氨基酸（DFAAs）的研究，并将新的重点放在公海上。DFAAs是有机碳和氮的重要来源，是生物不稳定溶解有机质（DOM）的优良模型。现在已知DOM通量是海洋碳和氮循环的主要部分。最近的工作表明，小型DFAA池的周转非常快，这表明需要修改这一领域以前的想法。这一建议包括对少营养型和深海中DFAA的周转、通量和可用性的广泛研究，从这些研究中获得的可靠数据很少。其他提议的工作包括测量浮游动物粪便颗粒中DFAA的释放，微生物对DFAA突然富集的反应（可能在“富集微区”中发现），DFAAs的藻类同化，DFAAs的铵再生，以及肽和蛋白质的降解。除了常用的氚化示踪剂外，在某些工作中，氨基酸氮的命运将用短寿命同位素N-13进行追踪。这种同位素具有非常高的比活度，因此它可以以很高的灵敏度添加到真正的痕量水平。但是由于它的使用寿命很短（约90分钟），样品必须被运送到回旋加速器，所以在这些实验中，需要使用直升机对近海水域进行取样。

This renewal proposal from Dr. Fuhrman is for an extension of studies on dissolved free amino acids (DFAAs), with new emphasis on the open sea. The DFAAs are important sources of organic C and N, and represent excellent models of biologically- labile dissolved organic matter (DOM). DOM flux is now known to be a major part of the marine C and N cycles. Recent work demonstrating very rapid turnover of small DFAA pools has shown a need to revise previous ideas in this area. This proposal includes extensive studies of DFAA turnover, flux, and availability in the oligothrophic and deep ocean, from which reliable data are sparse. Other proposed work includes measuring DFAA release from zooplankton fecal pellets, the microbial responses to sudden DFAA enrichment as might be found in "enriched microzones," algal assimilation of DFAAs, ammonium regeneration from DFAAs, and degradation of peptides and proteins. In addition to the usual tritiated tracers, for some of this work the fate of the amino acid nitrogen will be traced with the short-lived isotope N-13. This isotope has a very high specific activity, so it can be added at true trace levels with great sensitivity. But due to its brief useful lifetime (ca. 90 min.), samples must be transported to the cyclotron, so for these experiments the use of a helicopter to sample offshore waters is required.