Abstract:
Farmland N
2O emission is a popular topic in climate change research. Climate change (elevated CO
2 concentrations and increased temperatures) and farmland management measures are key factors affecting N
2O emissions in soil. Slow-release fertilizers are considered to have a positive effect on reducing N
2O emissions. It is unclear how the interaction between climate change and slow-release fertilizers affects N
2O emissions. Thus, we combined the local wheat-soybean cultivation model to investigate the potential impact of applying slow-release fertilizers on soil N
2O emissions during the growing season of subsequent crop under elevated CO
2 concentrations and increased temperatures. In this study, two air temperatures (ambient temperature and ambient temperature + 2 ℃) and two CO
2 concentrations (400 μmol∙mol
−1 and 600 μmol∙mol
−1) were set in the controlled chambers. Two fertilizers (conventional urea and slow-release urea) were applied during the wheat season under various environmental treatments in a wheat–soybean rotation system. Still, no fertilizer was used during the soybean growing season. CK referred to the ambient CO
2 concentration and temperature simulated in the controlled chamber (the ambient environmental CO
2 concentration in this experiment was 400 μmol∙mol
−1, and the environmental temperature was controlled by the intelligent control system to be consistent with the external environment). N
2O emissions during the entire growth period of soybean, soil ammonium nitrogen and nitrate nitrogen contents, and activities of soil enzymes involved in nitrification and denitrification during the drumming and ripening stages of soybean were measured. The results indicated that N
2O emissions from soybean-grown soil were mainly concentrated during the later growth period of soybeans. Compared to the application of conventional urea, the application of slow-release fertilizer in wheat-grown soil reduced total N
2O emissions by 38.46% during the soybean growth period under increased temperature (ET) alone, whereas the application of slow-release fertilizer increased total N
2O emissions in soybean-grown soil by 80.76%, 82.35%, and 11.96% under the CK, elevated CO
2 concentration (EC) alone, and co-elevation of atmospheric CO
2 concentration and temperature (ECT) treatments, respectively. Compared to the CK treatment, ET accelerated the conversion of ammonium nitrogen to nitrate nitrogen in soybean-grown soil at the seed filling stage, enhancing nitrate reductase activity and increasing N
2O emissions. In addition, EC alone had no effect on N
2O emissions from soybean-grown soil compared to the CK treatment. ECT resulted in a slight increase in nitrate and ammonium nitrogen contents in soybean-grown soil compared with the CK treatment, which was mainly attributed to the increase in nitrate reductase activity that might promote N
2O emissions; however, there was no significant difference in N
2O emissions in soybean-grown soil when ECT was compared with ET under conventional urea. In conclusion, N
2O emissions did not increase with elevated CO
2 concentration alone. N
2O emissions were expected to increase under elevated temperatures in the future, and the rational application of slow-release fertilizers in wheat-grown soil can increase the available nitrogen content in the soil, thus reducing N
2O emissions in soybean-grown soil. Our study highlights that slow-release fertilizers have greater potential to reduce N
2O emissions under climate change scenarios.