Regulating the Tempo of Nitrogen Turnover in Soils: Microbial and

在大多数陆地生态系统中，氮是限制植物生长的养分，但在某些情况下，过量的氮可能会对环境产生负面影响。过去的工作强调无机形态的氮；然而，在许多生态系统中，溶解的有机氮是一个更大的池。关于溶解有机氮池的生产和消费速度，人们知之甚少。本研究将为研究土壤中溶解有机氮的动态变化提供一种新的方法。该方法是对通常用于研究土壤无机氮库周转的“同位素稀释”技术的改进。这种新方法将产生溶解的有机氮，并用稳定的同位素(15N)进行标记。标记的溶解有机氮将被添加到土壤中以跟踪其消耗，方法是将标记追踪到其他氮库，并通过测量添加的(标记的)溶解有机氮在被自然微生物活动形成的未标记的溶解有机氮取代时的稀释程度来进行生产。如果成功，这种同位素稀释方法的新应用将为生态系统科学家研究氮循环的一个重要但鲜为人知的方面提供一个强大的工具。它将应用于自然生态系统和受管理的生态系统。更广泛地说，使用这种方法可能提供的见解可能使我们能够在提高植物生产力的同时将有害的环境影响降至最低。

Nitrogen is the nutrient that limits plant growth in most terrestrial ecosystems, but in some cases excess nitrogen can have negative environmental impacts. Past work has emphasized inorganic forms of nitrogen; however, in many ecosystems dissolved organic nitrogen is a larger pool. Relatively little is known about the rates of production and consumption of the dissolved organic nitrogen pool. This study will develop and test a new method to study the dynamics of dissolved organic nitrogen in soil. The method is a modification of the "isotope dilution" technique commonly used to study the turnover of inorganic soil nitrogen pools. The new method will produce dissolved organic nitrogen that is labeled with a stable isotope (15N). The labeled dissolved organic nitrogen will be added to soil to follow its consumption, by tracing the label into other nitrogen pools, and production, by measuring the dilution of the added (labeled) dissolved organic nitrogen as it is replaced by unlabeled dissolved organic nitrogen formed by natural microbial activity. If successful, this new application of the isotope dilution approach will provide a powerful tool for ecosystem scientists to study an important, but poorly understood aspect of the nitrogen cycle. It will have applications to both natural and managed ecosystems. More broadly, the insights that may be provided by the use of this approach may enable us to enhance plant productivity while minimizing detrimental environmental effects.