Workshop on Advanced Approaches to Quantify Denitrification

在过去的几十年里，在天然陆地生态系统中，食物和能源生产向生物圈引入的活性氮(N)一直大于固氮速率。到目前为止，人类在所有尺度上控制氮循环的最大不确定性是在反硝化的最后一步中，被转化回氮气的活性氮量。如果没有这些知识，就不可能确定活性氮在大多数环境水库中的积累率，因此也不可能评估其长期后果。氮与碳和其他营养循环相互作用，并对水、空气质量和气候产生许多级联影响。更好地了解活性氮在哪里、何时以及有多少被反硝化，有助于找到解决环境中过量活性氮造成的问题的解决方案。不幸的是，我们对景观和水域的反硝化速率知之甚少。我们知道发生反硝化作用的环境条件，但在野外可靠地量化氮气产量仍然相对罕见。对氮气生产缺乏了解的主要原因有三个：(1)由于大气背景浓度高，很难测量；(2)氮气生产速率在空间和时间上非常不均匀；(3)确定氮气生产速率的科学界之间缺乏协同作用。我们建议在2004年5月举办一个为期3天的研讨会，约35人参加，重点是通过生物反硝化来量化氮气产量。这次研讨会的目标是：(1)评估我们对各种陆地和水生生态系统中反硝化率的了解情况；(2)比较不同科学学科所采用的方法，期望跨学科的合作可以产生方法学上的进步；(3)找出目前的弱点和解决这些弱点所需采取的行动，以便改进对生物圈中活性氮在哪里、何时以及有多少转化为氮的全球评估。两个重要的考虑因素将叠加在生态系统类型和方法的矩阵上：(1)可以和应该测量氮气生产的适当尺度是什么？(2)如何将模型与测量相结合，以改进对过程的机械理解，并允许在更大的空间尺度、更长的时间尺度和一系列预测的情景中估计通量？研讨会的成果将作为一篇或多篇综合论文发表在同行评议的期刊上。这项活动的更广泛的影响包括努力引导我们对N循环的科学理解，以找到解决社会对生物圈富营养化的关注的办法。拟议的讲习班是国际氮气倡议(INI)的一个组成部分，该倡议是Scope和IGBP的一个联合项目。INI的总体目标是优化氮在可持续食品和能源生产中的作用，同时将对人类健康和环境的负面影响降至最低。因此，这次研讨会是一项对社会具有广泛影响的努力的一部分，它为未来的管理提供了知识，以实现全球氮循环，以实现粮食安全和环境质量的目标。

During the last few decades, the introduction of reactive nitrogen (N) into the biosphere by food and energy production has been greater than rates of N fixation in native terrestrial ecosystems. By far the largest uncertainty about the human domination of the N cycle on all scales is the amount of reactive N that is converted back to N2 during the last step of denitrification. Without this knowledge, it is impossible to determine the rate of accumulation of reactive N in most environmental reservoirs, and thus impossible to assess its long-term consequences. Nitrogen interacts with carbon and other nutrient cycles and has numerous cascading effects on water and air quality and climate. An improved understanding of where, when, and how much reactive N is denitrified could contribute to finding solutions to the problems created by excessive reactive N in the environment. Unfortunately, we have little knowledge about rates of denitrification across landscapes and waterscapes. We know the environmental conditions under which denitrification occurs, but reliable quantification of N2 production in the field is still relatively rare. There are three primary reasons for lack of knowledge about N2 production: (1) it is difficult to measure due to the high atmospheric background concentrations; (2) N2 production rates are very heterogeneous in space and time; and (3) there is a lack of synergy between the scientific communities that determine N2 production rates. We propose holding a 3-day workshop in May 2004 of about 35 participants to focus on quantification of N2 production via biological denitrification. The objectives of this workshop will be: (1) to evaluate the state of our knowledge of denitrification rates in a wide range of terrestrial and aquatic ecosystems; (2) to compare methodologies that have been adopted by different scientific disciplines, with the expectation that collaborations across disciplines could yield methodological advances; and (3) to chart out the current weaknesses and the actions needed to address those weaknesses for an improved global assessment of where, when, and how much reactive N is converted to N2 in the biosphere. Two important considerations will be superimposed over a matrix of ecosystem types and methodological approaches: (1) What are the appropriate scales over which N2 production can and should be measured?; and (2) How can models be integrated with the measurements to improve mechanistic understanding of the processes and permit estimation of fluxes at larger spatial scales, longer temporal scales, and across a range of forecasted scenarios? The results of the workshop will be published as one or more synthesis papers in a peer-reviewed journal. The broader impacts of this activity include an effort to direct our scientific understanding of the N cycle toward finding solutions to society.s concerns about eutrophication of the biosphere. The proposed workshop is being organized as an integral part of the International Nitrogen Initiative (INI), a joint project of SCOPE and IGBP. The overall goal of the INI is to optimize nitrogen's role in sustainable food and energy production, while minimizing negative effects on human health and the environment. Hence, this workshop is part of an effort that has board implications for society by contributing knowledge to future management the global N cycle to meet objectives of both food security and environmental quality.