Study On Agroecosystem Carbon Moving And Driving Factors In The Valley Of Manas River

This Global warming is the result of increased CO2 emissions from anthropogenic greenhouse gases,and the global consensus is that reducing greenhouse gas emissions is a key way to mitigate climate change.The ocean is recognized as a carbon sink system,but the carbon sink function of terrestrial ecosystem is very complex,and there is a large uncertainty.The farmland ecosystem plays an important role in carbon sink function.From the research hotspot and the analysis,there is not enough emphasis on the carbon sink function of agricultural ecosystem in arid area.Xinjiang is a typical representative of the arid areas,and there was carried on the massive land development,oasis agriculture scale expands unceasingly,an oasis of advanced irrigation technology popularization and other oasis agricultural management intensive degree enhances unceasingly since 1950s,which significantly changed the carbon sink function of oasis system.This study aimed to explore tempo-spatial patterns of carbon budgets and the mechanisms of its responses to the change of agricultural management.By using real-time monitoring and biogeochemical cycle model,we studied the change of tempo-spatial patterns of carbon budgets and its responses to the oasis expansion and climate fluctuations in field ecosystem in arid areas.Firstly,to reveal the response relationship between cotton carbon flux and the meteorological factors and planting pattern optimization on the farmland water use efficiency and irrigation efficiency,we studied the carbon flux variation under drip irrigation cotton field and cotton yield and water consumption under different planting patterns,which based on the eddy covariance and soil respiration data?2009-2013?.Secondly,using these site data validation Biome-BGC,and simulate the effect of agricultural management on the farmland ecosystem carbon balance.Finally,estimated the tempo-spatial patterns of carbon balance from 1970 to 2013 by BIOME-BGC model on 1km×1km grid scale.And carried out the simulation and prediction analysis of different scenarios which aimed on climate change,oasis expansion and agricultural management?fertilization,irrigation?.The results suggested that:1.Based on the eddy correlation system,we studied the carbon and water cycles under different cropping pattern.The results showed that:sowing,emergence and squaring dates were 13-20 d in advance in furrow irrigation under mulching?MF?and drip irrigation under mulching?MD?compared to furrow irrigation without mulching?NF?,and the whole life dates was extended for 12-16 d.The water use efficiency and irrigation water use efficiency were increased 65.2%and 62.3%in MD compared to NF.The gross primary production?GPP?and net ecosystem exchange?NEE?showed an obviously sinusoidal dynamic between daytime and nighttime,and the peak value occurred in 14:00.The seasonal variations of GPP and NEE were followed changes in LAI,and the peak value occurred in July.The GPP was assigned primarily to NEE from June to September and R_es in other months.The cumulative GPP averaged 816.2 gC m^-2 during the growing season,and about 58.6%of GPP was partitioned into NEE(meanly-478.6 gC m^-2)which showed a carbon sink.2.The soil respiration rate was measured by using soil respiration system under different straw management and fertilization treatments.The results showed that soil respiration rate has a significant seasonal characteristic,and the peak value occurred in mid-July and the minimum in January-February.The residue incorporation significantly increased soil respiration.The soil respiration rate under different fertilization treatments were shown as NPK+OM>OM>NPK>CK.There was a significant correlation between soil respiration and soil temperature,indicated that soil respiration was effected primarily by soil temperature.There was no significant seasonal variation under drip irrigation with mulching,resulted in there was no significant correlation between soil respiration and soil moisture.3.After irrigation and fertilization sub-model of BIOME-BGC model.It used the LAI,NPP and NEE data in Wulanwusu agrometeorological station.The results showed that the correlation coefficients between observed and simulated data of winter wheat,cotton and corn were 0.84,0.84 and 0.73,and root mean square errors were 0.75,1.05 and 1.33,respectively.The correlation coefficients between observed and simulated data of winter wheat and corn were 0.76 and 0.80,and root mean square errors were 39.46 and 25.33,respectively.The correlation coefficients and root mean square error between observed and simulated NEE data of cotton were 0.75 and 2.78,respectively.The results showed that the BIOME-BGC sub-model could simulated growth and NPP of winter wheat,cotton and corn.4.Simulated and estimated the NPP of oasis field ecosystem by using spatial Biome-BGC model.The total NPP in Manas River during 1970-2010 showed a trend of a significant increase,from 6.72 PgC m^-1 in 1970 increased to 12.36 PgC m^-1 in 2010,in which the contribution of cotton increased from 42%in 1970 to 89%in 2010.Oasis expansion effectively increased arable land,the cotton area was increased from 72.09 Kha in 1970 to152.25 Kha in 2010.Therefore,the CO₂ fixation of cotton was increased from 2.88 PgC m^-1in 1970 to 12.36 PgC m^-1 in 2010?about 4 times?,which was bigger than wheat or maize in this region.5.Comprehensive analysis the simulate NPP data by BIOME-BGC.The results showed that the contribution of the increased arable land was first,the agricultural management was second and climate change was third to NPP.Therefore,oasis expansion is the major factor for increasing NPP in nearly 40 years.Now,the large land reclamation is banned in Xinjiang,but improving the agricultural management can effectively increase the oasis farmland ecosystem carbon sequestration and reduce CO₂ emission.