The Effect Of Elevated Co₂ And Temperature On Soil N₂o Emissions

Impacts of climate change on soil nitrous oxide(N2O)emission from terrestrial ecosystems remain poorly understood.To quantify and better understand the extent of the impacts,and variations in N2O emissions from grasslands,croplands,and forests under different climatic conditions(elevated CO2,elevated temperature and their combination),we synthesized 209 measurements from 70 published studies before 2019 through meta-analysis.On average,a significant(P<0.05)increase of 23%in N2O emission was observed under elevated CO2(EC),across all case studies.A sharp increase in the N2O emissions was noticed in the response to EC(45%)under less than 150 ppm EC levels.When atmospheric CO2 concentration increases by more than 150 ppm and less than 300 ppm,soil N2O emission increased by 19%(P>0.05).When atmospheric CO2 concentration increment was greater than 300 ppm,soil N2O emission increased by 11%(P>0.05).There was a significant negative correlation between the EC and soil N2O emission(P<0.05),which may be because the continuous increase of CO2 concentration led to the decrease of available nitrogen in the soil and the decrease of substrate required for soil N2O production,thus reducing soil N2O emission.Compared with the positive responses of grassland and forest,EC resulted in the highest increase(38%)in N2O emission of cropland.In general,elevated temperature(ET)had no significant effect on soil N2O emission(P>0.05)across all studies.Response of the soil N2O emission to ET under different land use types also presented certain difference.The forest soil N2O emission increased by 20%(P>0.05),while grassland and farmland soil N2O emission was reduced by 16%and 4%respectively(P>0.05).This difference may be caused by the difference of soil C/N ratio between different land use types.When the temperature increase was less than 2?,the temperature increase resulted in a significant 32%increase in forest soil N2O emission(P<0.05),indicating that forest may become the main growth source of soil N2O emission under the background of warming.It was also found in this study that the effect of co-elevated CO2 and temperature on soil N2O emission was higher than that of EC or ET alone.Furthermore,the effect of future global warming and CO2 enrichment on soil N2O emissions may get stronger when terrestrial ecosystems become enriched in nitrogen and anthropogenic disturbance.