Warming-Induced Stimulation of Soil N₂O Emissions Counteracted by Elevated CO₂ from Nine-Year Agroecosystem Temperature and Free Air Carbon Dioxide Enrichment

Abstract

Globally, agricultural soils account for approximately one-third of anthropogenic emissions of the potent greenhouse gas and stratospheric ozone-depleting substance nitrous oxide (N 2 O). Emissions of N 2 O from agricultural soils are affected by a number of global change factors, such as elevated air temperatures and elevated atmospheric carbon dioxide (CO 2 ). Yet, a mechanistic understanding of how these climatic factors affect N 2 O emissions in agricultural soils remains largely unresolved. Here, we investigate the soil N 2 O emission pathway using a 15 N tracing approach in a nine-year field experiment using a combined temperature and free air carbon dioxide enrichment (T-FACE). We show that the effect of CO 2 enrichment completely counteracts warming-induced stimulation of both nitrification-and denitrification-derived N 2 O emissions. The elevated CO 2 induced decrease in pH and labile organic nitrogen (N) masked the stimulation of organic carbon and N by warming. Unexpectedly, both elevated CO 2 and warming had little effect on the abundances of the nitrifying and denitrifying genes. Overall, our study confirms the importance of multifactorial experiments to understand N 2 O emission pathways from agricultural soils under climate change. This better understanding is a prerequisite for more accurate models and the development of effective options to combat climate change.