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频繁出现的极端干旱事件会使水分循环的关键过程发生改变,进而显著影响生态系统的过程和功能.为了定量分析极端干旱对半干旱草原水分平衡的影响,利用内蒙古羊草(Leymus chinensis)草原生态系统通量观测站1978-2005年的气象数据、野外实测数据,对基于过程的生物地球化学循环模型——DNDC(Denitrifi cation-decomposition)进行参数化,模拟羊草草原生态系统2004-2005年各水分通量(蒸散、蒸腾、蒸发)和水分平衡的动态变化过程,分析极端干旱对蒸散、蒸腾、蒸发的影响.通过与涡度相关实测数据对比发现:参数化后的DNDC模型能够很好地模拟羊草草原生态系统的水分通量,在峰值大小和时间动态上,模拟值与实测值有较好的一致性(R2=0.68,P<0.0001),且实测和模拟结果都发现2005年的极端干旱使蒸散量显著降低(P<0.0001).基于参数化后的DNDC模型对植物蒸腾和土壤蒸发也进行了定量分离,发现与2004年相比,极端干旱使年蒸腾量降低了57%,年蒸散量降低了30%,生态系统由水分盈余转为严重的水分亏缺,进而使总初级生产力降低了73%,影响生态系统的碳源/汇功能.而且,羊草草原生态系统水分平衡发生改变的降水阈值为20.8 mm/月.本研究表明,极端干旱显著改变了植被蒸腾和土壤蒸发对蒸散的相对贡献,其对植被蒸腾的影响要远大于对土壤蒸发的影响.图5表1参58
The frequent occurrence of extreme drought events can change the key processes of the water cycle and significantly affect the ecosystem processes and functions.In order to quantitatively analyze the effects of extreme drought on the water balance in the semi-arid steppe, Leymus chinensis grassland ecology System flux observation station 1978-2005 meteorological data, the field measured data, the process of biogeochemical cycle model - Denitrifi cation-decomposition parameterized to simulate the sheep grassland ecosystem in 2004-2005 The effects of extreme drought on evapotranspiration, transpiration and evaporation were analyzed by comparing with the dynamic changes of moisture flux (evapotranspiration, transpiration, evaporation) and water balance. The comparison with the measured data of eddy covariance showed that the parameterized DNDC model can well The water fluxes of simulated Leymus chinensis grassland ecosystem were in good agreement with the measured values (R2 = 0.68, P <0.0001) in the peak size and time dynamics. Both the measured and simulated results showed that the Extreme drought reduced evapotranspiration significantly (P <0.0001). Plant transpiration and soil evaporation were also quantified based on the parametric DNDC model , Found that extreme drought reduced annual transpiration by 57% and annual evapotranspiration by 30% compared to 2004, and the ecosystem shifted from a surplus of water to a severe water deficit, thereby reducing total primary productivity by 73% Affecting the carbon source / sink function of the ecosystem.Moreover, the precipitation threshold of the water balance of Leymus chinensis steppe ecosystem was changed to 20.8 mm / month.The study shows that extreme drought significantly changed the relative contribution of vegetation transpiration and soil evaporation to evapotranspiration, Its effect on vegetation transpiration is much greater than on soil evaporation