Soil CO2 concentration (DP1.00095.001)

CO2 concentrations are measured at different depths in the soil to allow the gradient method to be used to estimate soil CO2 efflux rates when combined with other NEON data products. Soil CO2 efflux is an important component of the carbon cycle because it is one of the largest exchanges of carbon between terrestrial ecosystems and the atmosphere. In addition, since the vast majority of soil CO2 is produced by microbial, root and soil faunal respiration, soil CO2 efflux is an indicator of total soil biological activity. CO2 concentrations are measured in all five Instrumented soil plots per terrestrial site and at various depths below the soil surface starting at approximately 2 cm and data are presented as 1-minute and 30-minute averages. CO2 sensors at different depths within a soil plot are typically located within 1 m horizontally of one another. The CO2 concentration of soil air is measured at three depths within each plot, starting at approximately 2 cm. Latency: Data collected in any given month are published during the second full week of the following month. Soil CO2 concentration data from the NIWO site (mean elevation: 3490m) are currently flagged because the typical atmospheric pressure (~66 kPa) is below the manufacturer-specified lower range for pressure compensation (70 kPa). This data product is not currently available at the PUUM site (Hawaii) due to the initial soil characterization indicating the soil was too shallow to allow the standard soil temperature sensor to be installed. An alternative sensor was installed, but it is not currently compatible with the data processing pipeline (soil temperature is an input for the soil CO2 concentration data product). Future upgrades to the data processing pipeline will allow the data product to be produced, including retroactively, but this is not expected to occur soon. At four Alaskan sites (HEAL, BONA, TOOL, and BARR) the sensors experience frost heaving which regularly changes the measurement depths. New measurement depths are recorded when technician time and other priorities allow and depths are updated, but sensor depths may change between remeasuring events. In addition, the soil plots at HEAL have been subsiding faster than the surrounding area which may alter their representativeness of the overall site.本数据集通过测量土壤不同深度的二氧化碳浓度，结合其他NEON数据产品，可借助梯度法估算土壤二氧化碳排放通量速率。土壤二氧化碳排放是碳循环的重要组成部分，也是陆地生态系统与大气之间最大的碳交换途径之一。此外，土壤中绝大多数二氧化碳由微生物、植物根系及土壤动物的呼吸作用产生，因此土壤二氧化碳排放可作为土壤整体生物活性的指示指标。本数据集会在每个陆地站点的全部5个布设观测仪器的土壤样地中，于土壤表层以下约2厘米起的不同深度测量二氧化碳浓度，数据以1分钟和30分钟平均值的形式呈现。同一土壤样地内不同深度的二氧化碳传感器，在水平方向上通常彼此间距不超过1米。每个土壤样地内会在约2厘米起始的三个深度处测量土壤空气的二氧化碳浓度。数据发布延迟：当月采集的数据将于次月的第二个完整工作周内对外发布。来自NIWO站点（平均海拔3490米）的土壤二氧化碳浓度数据目前处于质量待核查状态，原因是该站点典型大气压（约66千帕）低于制造商规定的压力补偿下限值（70千帕）。夏威夷PUUM站点目前无法提供本数据产品，原因是初始土壤勘测结果显示该站点土壤过浅，无法安装标准土壤温度传感器。虽已加装替代传感器，但该传感器目前与数据处理流水线不兼容（土壤温度是土壤二氧化碳浓度数据产品的输入参数之一）。未来将对数据处理流水线进行升级，以支持本数据产品的生成，包括回溯生成历史数据，但预计短期内无法完成。阿拉斯加的四个站点（HEAL、BONA、TOOL及BARR）的传感器会受到冻胀影响，导致测量深度定期发生变化。仅当技术人员有空闲时间且优先级允许时，才会记录新的测量深度并更新参数，但两次重测之间传感器的深度仍可能发生变动。此外，HEAL站点的土壤样地沉降速度快于周边区域，这可能会降低其对整个站点的代表性。