Warming-Induced Stimulation of Soil N<sub>2</sub>O Emissions Counteracted by Elevated CO<sub>2</sub> from Nine-Year Agroecosystem Temperature and Free Air Carbon Dioxide Enrichment
Xiaoshun Tu, Jing Wang, Xiaoyu Liu, Yu Liu, Yinghua Zhang, Yves Uwiragiye, Ahmed S. Elrys, Jinbo Zhang, Zucong Cai, Yi Cheng, Christoph Müller
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.