Abstract Net ecosystem exchange of carbon dioxide (NEE) and soil respiration at field scale can exhibit considerable spatial variability linked to the heterogeneity of soil properties and state variables. In this study, we measured NEE with the eddy covariance (EC) method in a sugar beet field characterized by high spatial variability in soil physical properties. We further measured NEE and soil respiration by chambers as well as soil water content and temperature at 18 locations within the field. Spatially averaged chamber-measured NEE showed good agreement to the EC-based data. During a dry period high spatial variation of within-field NEE was detected with the chamber method. The coefficient of variation was on average 0.57 during the dry period, with a maximum of 0.72. Based on the depth-specific soil water content measurements the AgroC ecosystem model was inverted for soil hydraulic properties at each of the 18 locations, where soil water content was measured. Analyzing the model results revealed that root water uptake stress was the main driver of spatial and temporal variability in crop development and NEE, whereby the soil coarse material fraction (gravel content) and thickness of the layer above a gravel dominated soil layer were identified as the main influencing soil properties. The chamber-measured NEE and the flux footprint analysis showed that particularly during periods of severe root water uptake stress EC-based measurements would be prone to biases. A combination of the footprint model with the AgroC ecosystem model estimated a bias of 14 % for the dry period and a vegetation period bias of 6 % in relation to the average CO2 flux.

中文翻译：

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水分胁迫引起的甜菜林中二氧化碳通量田间变异性的量化

摘要 田间范围内二氧化碳 (NEE) 和土壤呼吸的净生态系统交换可以表现出与土壤特性和状态变量的异质性相关的相当大的空间变异性。在这项研究中，我们用涡度协方差 (EC) 方法测量了甜菜田中的 NEE，其特征是土壤物理性质的空间变化很大。我们进一步测量了小室的 NEE 和土壤呼吸以及田间 18 个位置的土壤含水量和温度。空间平均室测量的 NEE 与基于 EC 的数据显示出良好的一致性。在干旱期，使用腔室方法检测到场内 NEE 的高空间变化。干旱期变异系数平均为0.57，最大为0.72。基于特定深度的土壤含水量测量，AgroC 生态系统模型在 18 个测量土壤含水量的位置中的每个位置的土壤水力特性方面进行了反转。对模型结果的分析表明，根系吸水压力是作物发育和 NEE 时空变异的主要驱动因素，其中，砾石为主的土壤层上方的土壤粗物质分数（砾石含量）和层厚度被确定为主要影响土壤性质。腔室测量的 NEE 和通量足迹分析表明，特别是在严重的根部吸水压力期间，基于 EC 的测量容易出现偏差。