Department of Soil Science, North Carolina State University, Raleigh, NC 27695-7619, USA.
Environ Manage. 2012 Nov;50(5):861-74. doi: 10.1007/s00267-012-9929-z. Epub 2012 Aug 22.
Denitrification is a critical biogeochemical process that results in the conversion of nitrate to volatile products, and thus is a major route of nitrogen loss from terrestrial environments. Riparian buffers are an important management tool that is widely utilized to protect water from non-point source pollution. However, riparian buffers vary in their nitrate removal effectiveness, and thus there is a need for mechanistic studies to explore nitrate dynamics in buffer soils. The objectives of this study were to examine the influence of specific types of soluble organic matter on nitrate loss and nitrous oxide production rates, and to elucidate the relationships between these rates and the abundances of functional genes in a riparian buffer soil. Continuous-flow soil column experiments were performed to investigate the effect of three types of soluble organic matter (citric acid, alginic acid, and Suwannee River dissolved organic carbon) on rates of nitrate loss and nitrous oxide production. We found that nitrate loss rates increased as citric acid concentrations increased; however, rates of nitrate loss were weakly affected or not affected by the addition of the other types of organic matter. In all experiments, rates of nitrous oxide production mirrored nitrate loss rates. In addition, quantitative polymerase chain reaction (qPCR) was utilized to quantify the number of genes known to encode enzymes that catalyze nitrite reduction (i.e., nirS and nirK) in soil that was collected at the conclusion of column experiments. Nitrate loss and nitrous oxide production rates trended with copy numbers of both nir and 16s rDNA genes. The results suggest that low-molecular mass organic species are more effective at promoting nitrogen transformations than large biopolymers or humic substances, and also help to link genetic potential to chemical reactivity.
反硝化作用是一种关键的生物地球化学过程，导致硝酸盐转化为挥发性产物，因此是陆地环境中氮损失的主要途径。河岸缓冲区是一种广泛用于保护水免受非点源污染的重要管理工具。然而，河岸缓冲区在硝酸盐去除效果方面存在差异，因此需要进行机制研究以探索缓冲土壤中的硝酸盐动态。本研究的目的是研究特定类型的可溶性有机物对硝酸盐损失和氧化亚氮产生速率的影响，并阐明这些速率与缓冲土壤中功能基因丰度之间的关系。连续流动土壤柱实验研究了三种类型的可溶性有机物（柠檬酸、海藻酸和苏万尼河溶解有机碳）对硝酸盐损失和氧化亚氮产生速率的影响。我们发现，随着柠檬酸浓度的增加，硝酸盐损失速率增加；然而，添加其他类型的有机物对硝酸盐损失速率的影响较弱或没有影响。在所有实验中，氧化亚氮产生速率与硝酸盐损失速率相吻合。此外，定量聚合酶链反应（qPCR）用于量化在柱实验结束时收集的土壤中编码催化亚硝酸盐还原酶（即 nirS 和 nirK）的基因数量。硝酸盐损失和氧化亚氮产生速率与 nir 和 16s rDNA 基因的拷贝数呈趋势。结果表明，低分子量有机物质比大生物聚合物或腐殖质更有效地促进氮转化，并且还有助于将遗传潜力与化学反应性联系起来。
