Seasonally aggregated values of dissolved inorganic phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2003)

This data set contains measurements of inorganic phosphorus in samples of soil solution collected in 2003 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below) that have been aggregated to seasonal values. In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing.
Glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 µm (UMS GmbH, Munich, Germany) were installed in April 2002 in depths of 10, 20, 30 and 60 cm to collect soil solution. Manual soil matric potential measurements were used to regulate the vacuum system. Manual soil matric potential measurements were used to regulate the vacuum system. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled biweekly and analyzed for dissolved inorganic P (PO4P). Here volume-weighted mean values are provided as aggregated seasonal values (spring = March to May, summer = June to August, fall = September to November, winter = December to February) for 2003 in spring, fall, and winter. To calculate these values, the sampled volume of soil solution is used as weight for P concentrations of the respective sampling date.
Inorganic phosphorus concentrations in the soil solution were measured photometrically with a continuous flow analyzer (CFA SAN++, Skalar [Breda, The Netherlands]). Ammonium molybdate catalyzed by antimony tartrate reacts in an acidic medium with phosphate and forms a phospho-molybdic acid complex. Ascorbic acid reduces this complex to an intensely blue-colored complex. As the molybdic complex forms under strongly acidic conditions, we could not exclude the hydrolysis of labile organic P compounds in our samples. Furthermore, the molybdate reaction is not sensitive for condensed phosphates. The detection limits of both TDP and PO4P were 0.02 mg P l-1 (CFA, Skalar).

本数据集包含2003年采集自大型草原生物多样性实验（耶拿实验（Jena Experiment）；详见下文）主实验样地的土壤溶液（soil solution）样品中无机磷的测定数据，相关数据已被汇总为季节尺度均值。
该主实验共设置82块20×20米的草原样地，植物材料取自包含60个物种的种质库，这些物种分属4个功能群：禾本科植物、豆科植物、高大草本与小型草本。2002年5月，研究人员从该物种库中选取不同数量的植物物种播种至各块样地，以构建植物物种丰富度（1、2、4、8、16和60种）与功能群丰富度（1、2、3、4个功能群）的梯度样地。所有样地通过每年两次除草与刈割进行管护。

2002年4月，研究人员安装了直径12厘米、厚度1厘米、孔径1~1.6微米的玻璃吸力板（glass suction plates，UMS GmbH，德国慕尼黑），埋设深度分别为10、20、30与60厘米，用于采集土壤溶液。研究人员采用手动土壤基质势测定值调控真空系统。研究人员采用手动土壤基质势测定值调控真空系统。采样瓶持续抽至50~350毫巴的负压，使吸力压力较实际土壤水吸力高约50毫巴，仅收集土壤渗滤液。研究人员每两周采集一次累积土壤溶液，分析其中的溶解态无机磷（dissolved inorganic P, PO₄P）含量。本数据集提供了2003年春季（3月至5月）、秋季（9月至11月）与冬季（12月至2月）的季节尺度体积加权均值（原文标注的夏季时段为6月至8月，但本次未纳入相关数据）。该均值以各采样日期的土壤溶液采样体积为权重，对磷浓度进行加权计算得到。

土壤溶液中的无机磷浓度采用连续流动分析仪（continuous flow analyzer，CFA SAN++，Skalar，荷兰布雷达）通过光度法测定。在酒石酸锑钾的催化作用下，钼酸铵在酸性介质中与磷酸盐反应生成磷钼酸复合物，抗坏血酸可将该复合物还原为深蓝色复合物。由于该钼复合物的形成需要强酸性条件，本研究无法排除样品中不稳定有机磷化合物发生水解的可能性。此外，钼酸盐反应对缩合磷酸盐不敏感。总溶解磷（total dissolved phosphorus, TDP）与正磷酸盐磷（PO₄P）的检出限均为0.02 mg P·L⁻¹（CFA，Skalar）。