Inorganic and Organic Nitrogen Uptake Dynamics in the Equatorial Pacific during the Second Mesoscale Iron Enrichment Experiment (Iron Ex II)

小行星9504301 本研究将探讨天然植物群落对铁富集的氮动态响应。 在定于1995年5月至6月进行的下一次中尺度铁富集试验（Iron Ex II）期间，将使用稳定同位素15 N来量化赤道太平洋这一高营养、低叶绿素（HNLC）区域的硝酸盐、铵和尿素吸收。 本研究将获得准确、定量的天然组合氮素营养数据，以确定施铁是否提高新产量。 氮利用的粒度谱将通过使用不同孔径的过滤器在短期培养后收集颗粒物质来确定，因为细胞大小被认为是控制物质从表面沃茨沉降通量的主要因素（即出口生产，与新生产有关）。 将针对实验孵育期间可能发生的同位素稀释效应校正总样品和粒度分级样品的所有氮吸收速率，否则可能导致严重低估尿素和铵的计算氮吸收速率。 异养的贡献，总社区氮的吸收将确定利用尺寸分级技术和特定的代谢抑制剂，以区分异养细菌和自养浮游植物。 此外，放射性同位素3H将用于确定铁施肥导致的异养细菌生产的变化，这些数据以及细菌丰度的估计值将提供异养组合的生长速率的估计值。 确定的自养和异养的氮吸收率，连同定量的溶解有机氮（DON）释放在正常的15N示踪剂孵育和其对传统的措施的吸收，将允许准确估计新的和再生的生产在实验生态系统。 在这个拟议的含氮营养研究的实验是下一个中尺度铁富集研究的关键组成部分，其结果将是铁Ex II期间的生态系统对铁富集的全面理解的关键。

9504301 Cochlan This study will investigate the nitrogen dynamics of a natural planktonic community in response to iron enrichment. The stable isotope 15N will be used to quantify nitrate, ammonium and urea uptake in the equatorial Pacific Ocean, a high-nutrient, low-chlorophyll (HNLC) area, during the next mesoscale iron enrichment experiment (Iron Ex II) scheduled for May-June, 1995. The study will obtain accurate and quantitative data of the nitrogenous nutrition of the natural assemblage that will determination whether or not iron fertilization enhances new production. The size- spectrum of nitrogen utilization will be determined by using different pore-sized filters to collect particulate material after short-term incubations, since cell size is thought to be a major factor controlling the sinking flux of material from the surface waters (i.e. export production, which is related to new production). All nitrogen uptake rates of total and size- fractionated samples will be corrected for the effects of isotopic-dilution which may occur during the experimental incubation periods, a condition which otherwise could result in serious underestimation of calculated nitrogen uptake rates of urea and ammonium. The heterotrophic contribution to total community nitrogen uptake will be determined by utilizing size-fractionation techniques and specific metabolic inhibitors to distinguish between heterotrophic bacteria and autotrophic phytoplankton. Additionally, the radioactive isotope 3H will be used to determine the changes in heterotrophic bacterial production as a result of iron fertilization, and these data, together with estimates of bacterial abundance, will provide an estimate of growth rate for the heterotrophic assemblage. The nitrogen uptake rates determined for autotrophs and heterotrophs, together with quantification of dissolved organic nitrogen (DON) released during normal 15N-tracer incubations and its effect on traditional measures of uptake, will allow for accurate estimations of new and regenerated production in the experimental ecosystem. The experiments in this proposed nitrogenous nutrition study are a key component in the next mesoscale iron enrichment study, and their results will be critical for a comprehensive understanding of the ecosystem response to iron enrichment during Iron Ex II.