Warming Can Boost Denitrification Disproportionately Due to Altered Oxygen Dynamics

Abstract

BackgroundGlobal 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 FindingsWe 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/SignificanceOur 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.

Soil Degradation and the Decline of Available Nitrogen and Phosphorus in Soils of the Main Forest Types in the Qinling Mountains of China

“…Climate will have a profound effect on the decline of soil available N and P [20]. Temperature may enhance the soil microbial process and soil biochemical processes, such as denitrification, which are positively related to temperature [21]. Tree species can have a strong influence on soil properties [22].…”

Autotrophic Growth of Bacterial and Archaeal Ammonia Oxidizers in Freshwater Sediment Microcosms Incubated at Different Temperatures

“…For example, the decreased dissolved oxygen in the sediments associated with higher temperatures would be beneficial to anaerobes, such as denitrifiers or anaerobic ammonia-oxidizing (anammox) bacteria. It has been observed that rates of denitrification and anammox in sediment vary with temperature changes (47,48). Since denitrification activity and anammox bacteria-related sequences have been detected in Lake Taihu sediment (49,50), it is likely that the interactions between N-cycling processes as well as the ammonium assimilation by heterotrophs (51) in sedi- ments result in the low concentrations of nitrate at higher temperatures.…”

Climate Change Will Make Recovery from Eutrophication More Difficult in Shallow Danish Lake Søbygaard

“…Mechanisms responsible for higher P availability include higher mineralization rates and release from bottom sediments triggered by the higher temperatures. Concentrations of N, however, seem to decrease ( Figure 5C-E), which may partly be attributed to higher growth rates and thus greater nutrient uptake of phytoplankton, as well as increased bacterial denitrification rates [62]. Diatoms and cyanobacteria generally seem to benefit from higher water temperatures during summer, and diatoms from reduced nutrient conditions, while the effect on green algae is less pronounced (Figure 6D-F).…”