| Both natural and human-induced environmental changes have broadly influenced agricultural ecosystem sustainable development,because the various environmental stresses tend to interact with each other and exert a combined impact on ecosystem.Agricultural ecosystem is the important source of greenhouse gases and related to food security directly.It is critical to understand the effect of both natural and human-induced environmental changes on main crop yield and greenhouse gases emissions in China for food security and Climate Smart Agriculture strategy.However,previous studies had some problems 1)without synergistic effect of multiple environmental factors;2)without dataset and parameterization of the human activities and management measures in a large regional scale;3)without the combination of an ecosystem model and process-based crop model.Thus,we applied improved the agricultural module of Dynamic Land Ecosystem Model(DLEM-AG2.0)based on the DLEM-Ag module,to investigate the effects of multiple environmental factors(climate change,O2 concentration,tropospheric O3,nitrogen deposition,land use/cover change,N fertilizer an irrigation)on China main crop yield(wheat,maize,and rice),N2O and CH4 emission in ecosystems and probed the underlying mechanisms.The results and conclusions from this study were descried as following:(1)the DLEM-AG2.0 is capable of simulating the dynamic process of crop growth,leaf area expand,dry matter accumulation,yield formation,and greenhouse gas emission under different climatic condition and management practices.The simulated crop yield,biomass,and N2O/CH4 emission agree well with site-level and regional level observation.(2)China agricultural ecosystem experienced substantial environmental changes during 1980-2012.The increase trends of mean temperature,atmospheric CO2 concentration,atmospheric O3 concentration,and N deposition were significant(p?0.01).Precipitation showed large interannual variations.Maize fields increased at a 0.05x 108 ha yr-1 while both wheat and rice fields decreased at 0.02x 108 ha yr1.(3)The yields of China wheat,maize,and rice overall increased during 1980-2012 with the multiple environmental changes.However,compared with that in the 1980s,the increase trend in yield decreased by 52.6-99.5%in the 2000s.Meanwhile,N2O and CH4 emision in the crop fields increased by 27.2-54.3%and 20.1-34.7%,with a decrease trend of 88.2-150%and 150-300%in the 2000s compared to those in the 1980s,respectively.Both yield and greenhouse gas emission had significant temporal-spatial change.Climate change and elevated atmospheric O3 concentration induced a decrease of 39.8/%-64.9%and 4.5%-13.8%in crop yield during 1980-2012,respectively.Their negative effect on crop yield in China was aggravating.N fertilizer application played the dominant role in the increase of crop yield,and the next were atmospheric CO2 concentration and land use/cover change,following was atmospheric N deposition.The contribution of N fertilizer application and land use/cover to crop yield rise decreased in the 2000s while the contribution of atmospheric CO2 concentration and N deposition increased during the study period.(4)Climate change induced a decrease of 13.7-29.7%in N2O emission in crop fields during 1980-2012.The contribution of climate change to N2O emission was increasing.N fertilizer application played the dominant role in the increase of N2O emission,and the following were land use and cover change,atmospheric CO2 concentration,N deposition,and atmospheric O3 concentration.For CH4 emission increase,land use and cover change was the most important effect factor,and the next one was atmospheric CO2 concentration.The contribution of climate change to CH4 emission increase was larger than N fertilizer application and N deposition.Atmospheric O3 concentration inhibited CH4 emission increase. |
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