Evapotranspiration from the Jena-Ecotron experiment (including 12 soil monoliths with 4- and 16-species mixtures in year 2012)

This dataset contains community evapotranspiration derived from root water uptake as well as from weight changes from the 12 macrocosms used in the Jena-Ecotron Experiment in 2012. This experiment was conducted in the Montpellier European Ecotron (CNRS, France) an advanced controlled environment facility for ecosystem research, and aimed at understanding the impact of plant species richness (4 vs. 16 species) for ecosystem carbon and water fluxes. The soil monoliths used in this experiment contained plant communities originating from the long- term Jena Experiment (50°57.1' N, 11°37.5' E, 130 m above sea level; mean annual temperature 9.3°C, mean annual precipitation 587 mm) established in May 2002. Twelve plots from the Jena Experiment were selected for the Jena-Ecotron study according to the following criteria: (1) the four functional groups grasses, legumes, small and tall herbs were present, (2) realized species numbers were close to sown species richness, and (3) plots were equally distributed across the experimental field site to account for different soil textures. Large monoliths (2 m² surface area, diameter of 1.6 m, 2 m depth with a weight of 7 to 8 tons) including intact soil and vegetation were excavated from the twelve plots in December 2011 and placed in lysimeters. In March 2012, before the start of the vegetation growth, the lysimeters were transported and installed in the Macrocosms platform of the Montpellier European Ecotron. Ecosystem evapotranspiration (ET) was measured from the lysimeter weight changes to validate the ET estimated with a water balance method. The weight measurements (6 minutes resolution) were smoothed using a moving average over 30 minutes to reduce noise due to the experimental setup (Milcu et al. 2016). A water balance method was used to estimate daily root water uptake profiles and thus daily ecosystem ET from diurnal fluctuation of soil water content measurements (Guderle & Hildebrandt, 2015; doi:10.5194/hess-19-409-2015). The method consists in applying a running regression over multiple time steps on soil water content time series of each measurement depth. Here we used measurements with a temporal resolution of 1 minute from 10 cm, 20 cm, 30 cm and 60 cm depth. We split up the time series by fitting a linear function to each day and night branch of the time series in order to disentangle soil water flow and actual root water uptake. In a prior investigation we found the main transpiration time lasted from 5:30 am to 6:30 pm so that the onset of the day and night branch was fixed to these times. Night time transpiration was low (< 23 % of the day time transpiration) and therefore neglected (Milcu et al. 2016). Subsequently, the root water uptake profile was integrated over the entire soil profile to determine the ET per one m² surface and day. The modelled ET was furthermore multiplied by the factor two in order to upscale the modelled ET to the surface of one lysimeter which is two m². Evapotranspiration values estimated from weight changes between 5:00 am and 6:30 pm of the respective day are provided for 25 June 2012, 28 June 2012 and 29 June 2012. Evapotranspiration values estimated from root water uptake are provided for the days 25 June 2012, 28 June 2012, 29 June 2012, 17 July 2012 and 18 July 2012.本数据集包含基于根系吸水以及2012年耶拿生态箱实验（Jena-Ecotron Experiment）中12个大型模拟生态系统（macrocosms）的重量变化推导得到的群落蒸散发（evapotranspiration）数据。该实验于法国国家科学研究中心（CNRS, France）下属的蒙彼利埃欧洲生态箱（Montpellier European Ecotron）开展——这是一座用于生态系统研究的先进受控环境实验设施，旨在探究植物物种丰富度（4种 vs. 16种）对生态系统碳、水通量的影响。 本实验所用的土壤原状柱（soil monoliths）携带的植物群落源自长期耶拿实验，其地理坐标为50°57.1' N、11°37.5' E，海拔130米，年平均气温9.3℃，年平均降水量587 mm，该群落于2002年5月构建。本次耶拿生态箱研究从长期耶拿实验的样地中筛选出12块样地，筛选标准如下：（1）包含草本、豆科、小型草本与高大草本4个功能群；（2）实际定植物种数接近播种设定的物种丰富度；（3）样地在实验田块中均匀分布，以抵消土壤质地差异带来的影响。2011年12月，研究人员从这12块样地中挖掘出包含完整土壤与植被的大型原状柱——其地表面积为2 m²，直径1.6 m，深度2 m，重量7~8吨，并将其安置于蒸渗仪（lysimeters）中。2012年3月，在植被生长季启动前，这些蒸渗仪被转运并安装至蒙彼利埃欧洲生态箱的大型模拟生态系统平台。 为验证通过水量平衡法（water balance method）估算得到的生态系统蒸散发（evapotranspiration，简称ET），研究人员通过蒸渗仪的重量变化开展蒸散发测定。重量测定的时间分辨率为6分钟，为降低实验装置引入的测量噪声，研究人员采用30分钟移动平均法对数据进行平滑处理（Milcu等，2016）。 本研究采用水量平衡法，基于不同深度土壤含水量（soil water content）的日变化特征，估算每日根系吸水剖面，进而推导得到每日生态系统蒸散发（Guderle & Hildebrandt, 2015; doi:10.5194/hess-19-409-2015）。该方法的核心逻辑为：对各测定深度的土壤含水量时间序列，在多个时间步长上开展滑动回归分析。本研究采用了10 cm、20 cm、30 cm及60 cm深度、时间分辨率为1分钟的测定数据。研究人员将时间序列按每日昼、夜时段拆分，分别拟合线性函数，以区分土壤水分流动与实际根系吸水。前期预实验表明，主要蒸腾时段为每日5:30至18:30，因此将昼、夜时段的分界固定于此。夜间蒸腾量较低（不足日间蒸腾量的23%），故予以忽略（Milcu等，2016）。随后，将整个土壤剖面的根系吸水量进行积分，以得到单位地表面积每日的蒸散发量。此外，将模型估算的蒸散发乘以系数2，以将其尺度放大至单个蒸渗仪对应的地表面积（2 m²）。 本数据集提供了2012年6月25日、6月28日及6月29日这三天，基于对应日期5:00至18:30时段的重量变化估算得到的蒸散发值；同时提供了2012年6月25日、6月28日、6月29日、7月17日及7月18日这五天，基于根系吸水估算得到的蒸散发值。