Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands.
PLoS One. 2011 Mar 31;6(3):e18508. doi: 10.1371/journal.pone.0018508.
Global warming and the alteration of the global nitrogen cycle are major anthropogenic threats to the environment. Denitrification, the biological conversion of nitrate to gaseous nitrogen, removes a substantial fraction of the nitrogen from aquatic ecosystems, and can therefore help to reduce eutrophication effects. However, potential responses of denitrification to warming are poorly understood. Although several studies have reported increased denitrification rates with rising temperature, the impact of temperature on denitrification seems to vary widely between systems.
METHODOLOGY/PRINCIPAL FINDINGS: We explored the effects of warming on denitrification rates using microcosm experiments, field measurements and a simple model approach. Our results suggest that a three degree temperature rise will double denitrification rates. By performing experiments at fixed oxygen concentrations as well as with oxygen concentrations varying freely with temperature, we demonstrate that this strong temperature dependence of denitrification can be explained by a systematic decrease of oxygen concentrations with rising temperature. Warming decreases oxygen concentrations due to reduced solubility, and more importantly, because respiration rates rise more steeply with temperature than photosynthesis.
CONCLUSIONS/SIGNIFICANCE: Our results show that denitrification rates in aquatic ecosystems are strongly temperature dependent, and that this is amplified by the temperature dependencies of photosynthesis and respiration. Our results illustrate the broader phenomenon that coupling of temperature dependent reactions may in some situations strongly alter overall effects of temperature on ecological processes.
全球变暖以及全球氮循环的改变是对环境的主要人为威胁。反硝化作用，即硝酸盐向气态氮的生物转化，可从水生生态系统中去除大量氮，因此有助于减少富营养化的影响。然而，人们对反硝化作用对变暖的潜在反应知之甚少。尽管有几项研究报告称，随着温度的升高，反硝化速率会增加，但温度对反硝化的影响在不同系统之间似乎差异很大。
方法/主要发现：我们使用微宇宙实验、现场测量和简单的模型方法探讨了变暖对反硝化速率的影响。我们的研究结果表明，温度升高三度将使反硝化速率增加一倍。通过在固定氧浓度下以及在随温度自由变化的氧浓度下进行实验，我们证明反硝化作用的这种强烈的温度依赖性可以通过随温度升高而氧浓度系统性降低来解释。变暖会导致氧气浓度降低，这是由于氧气的溶解度降低，更重要的是，因为呼吸作用随温度的升高而比光合作用上升得更快。
结论/意义：我们的研究结果表明，水生生态系统中的反硝化速率对温度具有很强的依赖性，而光合作用和呼吸作用的温度依赖性放大了这种依赖性。我们的研究结果说明了更广泛的现象，即温度依赖性反应的耦合在某些情况下可能会强烈改变温度对生态过程的整体影响。
