Carbon Cycle Characteristics Of Vineyard Ecosystem In Arid Region

In the context of accelerating climate warming,farmland ecosystems are the ecosystems most affected by human activities,and their carbon pools have become very active.The arid region in northwest China has a fragile natural environment.Grapes,as an important economic crop widely planted in arid regions,have significant impact on regional carbon pools due to their vine structure and perennial properties.Studying the dynamic changes and mechanisms of carbon flux in vineyards is of great significance for understanding the carbon cycle process in arid regions.Based on the above reasons,carbon flux vineyards in northwestern China was measured using the soil carbon flux automatic observation system combined with the eddy covariance system from July 2013 to October 2017.In this paper,we tried to analysis the dynamic changes of different components of the carbon flux and quantify the annual total amount of each carbon component in the vineyard;evaluate the vineyard carbon source/sink function by using carbon footprint analysis method;distinguish the main driving factors and control mechanisms of each carbon component on different time scales;determine the parameters of the DNDC(DeNitrification?DeComposition)carbon cycle model,and discuss the response intensity of carbon flux in different scenarios.The main results are as follows:(1)Total soil respiration(TSR)and its different components(autotrophic respiration(AR)and heterotrophic respiration(HR))had different daily variation peaks.TSR,HR and AR showed consistent seasonal trends,and the contribution rate of AR to TSR varied between 15?63%with an annual average value of 37%.The 4?year average TSR,HR and AR average annual amounts were 739±71,457±38,and 282±84 g C m^-2 yr^-1,respectively.(2)Irrigation and nitrogen fertilizer strongly affected the daily amount of TSR,HR and AR.At different time scales,0?5 cm soil temperature(ST₅),0?5 cm soil water content(SWC₅)and total primary productivity(GPP)were important factors affecting TSR and HR and AR.It was necessary to consider the specific relationship between environmental variables and TSR on a specific time scale.(3)The diurnal variation of net ecosystem CO₂ exchange(NEE)was"W"shaped curve in sunny day due to midday depression of photosynthesis and there were two peaks at 12:00 and 14:00 at noon.Weather conditions,pruning and irrigation all significantly affected the daily variation of NEE.The vineyard growing season(April to September)had the strongest carbon sequestration in July and the weakest carbon sequestration in April.The average total amount of GPP,NEE and ecosystem respiration(ER)in 4 years were?1651±60,?573±68,1078±59 g C m^-2 yr^-1.The environmental factors that control NEE differed largely at different time scales.The main factors affecting hourly NEE were photosynthetically active radiation(PAR)and canopy conductance(G_c).The main factors affecting daily NEE were air temperature(T_air)and G_c.G_c was also main factor affecting monthly NEE.(4)The estimated 4?year average net carbon budget was?7806 kg CO₂-eq.hm^?2by using amount of net CO₂ absorption value minus the carbon footprint of grape production,which indicated that the vineyard is a carbon sink plant.(5)When using DNDC model to simulate the vineyard TSR and ER variations,the results were not as expected,but DNDC model could simulate NEE and GPP well.The average annual amount of ER,NEE and GPP were significantly affected by CO₂concentration,air temperature,surface soil(0?10 cm)organic matter content and tillage depth.N fertilizer and irrigation intensity had a limited impact on ecosystem carbon exchange after exceeding the required value.