| Global climate and environmental change has been characterized by atmospheric atmospheric CO2 enrichment and surface warming since pre-industrial times.The atmospheric CO2 concentration is projected to reach over 500 ppm,which may raise global surface air temperatures by about 2? during the middle of 21st century.China's agriculture is especially vulnerable to the impact of global climate change.The Chinese government has been active in exploring and adapting the impacts of climatic change on agriculture.However,it remains unclear about the impacts of climate change on agricultural production in China.Therefore,understanding the impact of global climate change on agricultural production processes is an urgent task.This study was conducted in an open field experiment with simulated climate change in rice-winter wheat rotation system for five years from 2010 to 2015 in Changshu Municipality,to investigate the impacts of atmospheric CO2 enrichment(up to 500 ppm)(CE),crop canopy air warming(+20C)(WA)and their combination(CW)on crop production,grain quality,nutrient and water utilization.We were trying to provide a scientific base for mitigating and adapting the impact of climatic change on agriculture.The main results obtained were as follows:1.Effects of CO2 enrichment and canopy warming on crop productionThe effect of climate change on grain yield was more prominent in wheat than in rice,and the positive effect of CO2 enrichment was unable to compensate for the negative impact of canopy warming on grain yield in rice.On averaged five years,CE caused a higher increase in grain yield by 10.8%,and WA caused a higher reduction in grain yield by 23.2%in wheat.The grain yield of rice followed a similar trend,with a less extent of change compared to wheat.However,CW had no effect on wheat yield,but it reduced rice grain yield by 4.6%.The impacts of CO2 enrichment and canopy warming on crop productivity showed pronounced variability.Our result here demonstrated that increment of grain yield by CE varied from 2.4%to 29.6%,and the decrement of grain yield by warming varied from 3.2%to 37.1%.The coefficient of variability was significantly increased by 16.4%and 40.9%for wheat and rice grain yield,respectively,under WA.2.Effects of CO2 enrichment and canopy warming on grain qualityChanges in grain yield partially explained the effect of climate change on grain quality,but the tradeoff between grain yield and quality could not fully offset the negative effect of climate change.CO2 enrichment increased grain yield,but reduced grain protein and amino acid concentrations by 8.7?14.g%for wheat and 3.3?7.0%for rice;warming increased grain amino acid by 5.4%for wheat and 5.8%for rice,due to greater reduction in grain yield.The effect of climate change on grain quality was more prominent in wheat than in rice,but the impacts of climate change on grain quality could be difficult to predict on the basis of single factor experiments.Our results here demonstrated that CO2 enrichment caused reduction in grain protein and amino acid concentrations for both wheat and rice,but the decrements of wheat by 14.9%and 8.7%were higher than that of rice by 7.0%and 3.3%,respectively.Furthermore,warming reduced grain protein accumulation by 12.9%in wheat,but not in rice.However,there were significant interaction effects between CO2 and canopy warming on grain protein accumulation and rice amino acid accumulation,suggesting that the effects of concurrent CO2 enrichment and canopy warming were not simply additive effect of individual effect of CO2 enrichment and canopy warming.Warming moderately mitigated the negative impacts of CO2 enrichment on grain nutrient concentration,but they synergistically posed a threat on the allowed toxic metals in grain.CO2 enrichment reduced grain nutrient concentration by 4.2?20.1%,but increased Cr,Cd and Pb concentrations;warming consistently increased most of elements concentrations by 4.0?81.6%;under CW,grain nutrient concentrations were unchanged,but the toxic metals(Mn,Mo,Cr,Ni,Cd,Pb)were significantly increased by 25.3%,46.5%,138.0%,54.6%,155.3%,75.7%in wheat and 22.3%,27.7%,178.3%,102.1%,94.4%,44.5%in rice,and the extents of change were higher than CE and WA treatments.3.Effects of CO2 enrichment and canopy warming on N,P and K uptake and utilizationThe effects of CO2 enrichment and canopy warming on nutrient uptake and utilization varied among crop and nutrient types.Atmospheric CO2 enrichment reduced N and K concentrations by 5.4%and 12.5%,respectively,in wheat,and decreased N and K concentrations by 7.5%and 8.2%in rice,respectively,but unchanged nutrient accumulation,and slightly increased N and K utilization efficiency,whereas had no significant effect on P uptake and utilization.By contrast,warming generally increased N and P concentrations by 22.7%and 12.1%,respectively,in wheat,but decreased N,P and K accumulation by 12.6%,10.9%and 15.3%,respectively,in rice,and reduced N utilization efficiency by 18.1%in wheat,suggesting that warming increased nutrient concentrations in plant at the cost of reducing biomass,and reducing nutrient utilization.Therefore,improving nutrient supply could be an effective approach for mitigating the negative impacts of climate change on crop production.Individual treatment of CO2 enrichment and canopy warming had no significant effects on nutrient utilization efficiency,but combined treatment enhanced N utilization efficiency rice in 2013 and K utilization efficiency in rice in 2014,indicating that the impacts of concurrent CO2 enrichment and canopy warming on nutrient uptake and utilization were completely different compared with individual effect from CO2 enrichment and temperature.Moreover,significant interaction between CO2 and temperature was observed for nutrient uptake and utilization.Therefore,combined treatment was more complex than individual treatment,and that the impacts of climate change on nutrient uptake and utilization could be difficult to predict from single factor experiments.4.Effects of CO2 enrichment and canopy warming on micronutrient availability and uptakeAtmospheric CO2 enrichment and canopy warming have positive effects on micronutrient availability.CO2 enrichment caused increases in availabilities of micronutrient by 22.5?114.1%for wheat,and increased availabilities of Cu and Zn by 15.4%and 20.8%,respectively,for rice.Under warming conditions,the availabilities of micronutrient were increased by 15.3?60.4%for wheat,and the availabilities of Fe and Mn were increased by 24.9%and 41.1%,respectively,for rice.Furthermore,CW moderately increased soil micronutrient availability.Warming overweighed CO2 enrichment in altering micronutrient uptake.CE generally had no significant effects on micronutrient transfer coefficient and concentrations in aboveground plant,although it increased micronutrient accumulations due to higher biomass.However,WA significantly increased micronutrient transfer coefficient and concentrations in aboveground.These results suggested that micronutrient cycling were more affected by warming compared with CO2 enrichment under climate change.5.Effects of CO2 enrichment and canopy warming on agricultural water utilizationThe negative impact of canopy warming outweighed the positive effect of CO2 enrichment on water utilization.Under CO2 enrichment,crop water requirement(CWR)was slightly decreased by on average of 8.3%,but water utilization efficiency of grain yield(WUEg)and biomass(WUEb)were increased by 23.1%and 20.6%,respectively;by contrast,warming increased CWR by an average of 19.6%,and caused increases in WUEg and WUEb by 27.9%and 29.3%,respectively;however,under CW,the CWR was increased by 3.1?15.8%,and the WUEg and WUEb were increased by 3.5?26.7%compared with ambient conditions.An interaction of CO2 enrichment and canopy warming contributed to inter-annual variation in CWR and WUE.The coefficient of variability showed that CE slightly reduced the variation of WUE,and canopy warming increased inter-annual variation of WUEb rather than WUEg,but CW consistently increased variations of CWR and WUE by 30.6?57.3%.In conclusion,atmospheric CO2 enrichment caused increases in grain yield and biomass,reduction in crop water requirement,and indirectly affected soil processes(e.g.increases in soil microbial biomass,and nutrient availability),but decreased grain quality,nutrient concentrations due to dilution effect;in contrast,warming increased leaf transpiration,and greatly decreased grain yield,results in high grain amino acid and nutrient concentration at the expense of reducing grain yield,while significantly increased toxic metal concentrations in grain.It is worth noting that there were synergetic,antagonistic and complex interactive effects between CO2 enrichment and canopy warming on agroecosystem processes.Under simultaneously CO2 enrichment and canopy warming,the positive effects of CO2 enrichment on crop production and crop water utilization were unable to compensate for the negative impacts of canopy warming,but synergistically enhanced variations of grain yield and water use and toxic metal concentrations in grain.However,the tradeoff between the effects of CO2 enrichment and canopy warming could not fully offset the negative impacts of climate change.Furthermore,the effects of CO2 enrichment and canopy warming on agroecosystem processes changed among crop types,with the effect of climate change more prominent in wheat than in rice.Overall,these results suggested that the impacts of climate change are difficult to be evaluated and predicted based on the individual treatment or single process. |
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