| Since the industrial revolution,global temperature and atmospheric CO2 concentration have been increasing year by year.As an important‘source’ and‘sink’ of greenhouse gas,agricultural soil is very sensitive to climate change.Nitrous oxide(N2O)is an important agricultural greenhouse gas.It has greater global warming potential than CO2.Although it is still uncertain that how climate change impacts greenhouase gases emission,reducing N2O emission and increasing soil carbon sequestration have become an important means to mitigate climate change in agriculture.Although a series of research and policies have been implemented to mitigate climate change,global temperatures and atmospheric CO2 concentrations are still rising further.At present,choosing low-emission crop variety,applying nitrification inhibitors and biochar-based fertilizers are widely used to reduce N2O emissions from agricultural soils.However,their impacts on N2O emission under atmospheric CO2 enrichment and warming has not been evaluated.In order to clarify how atmospheric CO2 enrichment and warming affect agricultural greenhouse gas emissions and look for an effective emission reduction measure under climate change.A field experiment with simulated climate change was used to evaluat greenhouse gas emission reduction potential of different emission reduction measures under atmospheric CO2 enrichment and warming.In addition,incubation experiments were employed to investigate the effects of soil biological characteristics and litter quality on organic carbon mineralization under atmospheric CO2 enrichment and warming.The main results obtained were as follows:1.Four wheat varieties including Yangmai 16,Sumai 188,Zhenmai 9,and Xinnong 518 were grown under atmospheric CO2 enrichment and warming(control,CT;atmospheric CO2 enrichment,C+T;warming,CT+,atmospheric CO2 enrichment and warming,C+T+).The yield,nutrients uptake,and greenhouse gas emissions were determined to comprehensively evaluate the emission reduction potential of different wheat varieties.The results showed that the yield responses to atmospheric CO2 enrichment and warming were similar among the different wheat varieties.Atmospheric CO2 enrichment increased wheat yiled,while warming reduced the yield.However,the nutrient uptake responded differently to atmospheric CO2 enrichment and warming among the different wheat varieties,especially N uptake.This would affect the response of N2O emissions among different wheat varieties to atmospheric CO2 enrichment and warming.Under atmospheric CO2 enrichment,Sumai 188 has the largest increase in total N uptake(27.54%);and it was also the only one whose cumulative N2O emissions had decreased under atmospheric CO2 enrichment.Zhenmai 9 had the smallest increase in total N uptake,and was the species with the largest increase of N2O emissions(37.86%)under warming.While,the total uptake of N in Sumai 188 and Yangmai 16 decreased more,and the N2O emissions decrease less under warming.Combining yield and greenhouse gas emissions,Zhenmai 9 was greatly affected by climate change and has reduced production and increased emissions.Whereas,Yangmai 16 and Sumai 188 had relatively higher yield and lower N2O emision.2.As means of reducting greenhouse gases emission,nitrification inhibitors and biochar-based fertilizers were evaluated under climate change.Except CT,C+T,CT+and C+T+,three different fertilizer methods were set including common fertilizer(CF),fertilizer with nitrification inhibitor(CP)and biochar-based fertilizer(BF).The yield,N2O emission,potential nitrification rate,potential denitrification rate,and gene abundances were determined to comprehensively evaluate the greenhouse gas reduction potential and mechanism of nitrification inhibitors and biochar-based fertilizers under climate change.The results showed that nitrification inhibitor increased the yield of wheat by 4.82%.Compared with common fertilizers,nitrification inhibitors still maintained an increase in yield under atmospheric CO2 enrichment and warming.Nitrification inhibitors reduced the cumulative N2O emissions(15.77%)by reducing the soil nitrification rate,amoA gene abundance,inhibiting the conversion of soil NH4+-N to NO3--N,reducing the substrate of the denitrification process,and reducing the nirS gene abundance.Moreover,nitrification inhibitors still showed a significant effect on emission reduction under atmospheric CO2 enrichment and warming.Compared with nitrification inhibitors,biochar-based fertilizers had no significant effect on wheat yield.However,biochar-based fertilizers showed an increase in yield under atmospheric CO2 enrichment and warming.Although biochar-based fertilizers did not affect the soil nitrification and denitrification rates,it showed a stimulating effect on N2O emissions.While the cumulative N2O emissions increased by 8.06%,the gene abundance of AOB increased by 33.73%,and the abundance of nirS and nosZ decreased by 27.41%and 32.34%.Atmospheric CO2 enrichment did not affect the increase of biochat-based fertilizer on N2O emissions,while warming stimulated the N2O emissions.The changes in the abundance of the nosZ gene may be the key in effects of warming and increasing atmospheric CO2 concentration on the carbon-based fertilizer’s emission reduction effect.3.Through incubation experiments,we studied the importance of soil microbiological characteristics and litter quality changes under atmospheric CO2 enrichment and warming on soil organic carbon mineralization.Three experiments were set,one:CT*CT、C+T*C+T、CT+*CT+,and C+T+*C+T+;two:CT*CT、CT*C+T、CT*CT+,and CT*C+T+;three:CT*CT、C+T*CT、CT+*CT,and C+T+*CT.The results showed that compared with CT*CT,the cumulative mineralization of C+T*C+T was significantly reduced by 27.62%in the aerobic stage.The cumulative mineralization of C+T*CT also decreased significantly by 25.45%,but C+T+*CT increased by 35.54%.In the anaerobic stage,there was no significant difference of cumulative mineralization between all treatments.Although the accumulated mineralization of soil organic carbon was significantly correlated with ΔDOC(p<0.05)and extremely significantly correlated with AMBC(p<0.01),it did not appear to be significantly correlated with DOC and MBC.In summary,the changes in the quality of straw litter did not have a significant impact on the turnover of soil organic carbon.The changes in the soil microbiological characteristics affected the soil ability to carbon sequestration:warming didn’t show a significant effect,while atmospheric CO2 enrichment promoted the accumulation of soil organic carbon and increased N2O emission.It is worth to note that the mineralization of organic carbon had increased significantly under atmospheric CO2 enrichment and warming.Both biochar-based fertilizers and nitrification inhibitors increased the wheat yield and reduced N2O emissions under atmospheric CO2 enrichment and warming.The biochar-based fertilizer showed a low emission trend in the early stage of wheat,but the nitrification inhibitor was significantly affected after the wheat turned green.Applying biochar-based fertilizer as the base fertilizer and nitrification inhibitor CP when returning to green with urea may be an effective way to increase crop yield and mitigate climate change under the future climate change.It also decreases economic costs and harm to the environment. |
