Effect of rice-straw biochar on nitrous oxide emissions from paddy soils under elevated CO2 and temperature.

In paddy ecosystems, the feedback of N2O emissions on climate change as well as the effects of biochar on N2O emissions will have a profound impact on global warming and rice production. In order to investigate the effect of biochar amendment on N2O emissions from paddy soils under elevated atmospheric CO2 concentration (700ppm) and air temperature (ambient +3°C), a microcosm study was performed in plant growth chambers with rice plant and rice-straw-derived biochar. N2O emissions from urea-fertilized paddy soils had a significant increase with the biochar amendment during midseason drainage under ambient CO2 concentration and air temperature. However, N2O emissions was suppressed under simultaneous elevated CO2 concentration and air temperature, regardless of whether biochar was amended; under this condition the stimulating effect of biochar was attenuated. Reduced mineral N concentrations and increased DOC concentrations could inhibit N2O emission at simultaneously elevated CO2 concentration and air temperature. Increased soil pH and variation in the abundance of archaeal and bacterial amoA genes indicated that biochar amendment could stimulate ammonia oxidation-induced N2O emission during nitrification. Moreover, the liming effect of biochar was lessened under elevated CO2 concentration and temperature, which may contribute to the attenuated stimulating effect of biochar on N2O emissions. More attention should to be paid to the effect of soil pH-induced changes in ammonia oxidation, when mitigating N2O emissions in urea-fertilized paddy soils with biochar amendment at elevated CO2 concentrations and air temperatures.