Dissolved phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2002)

This data set contains measurements of dissolved phosphorus (total dissolved nitrogen: TDP, dissolved inorganic phosphorus: PO4P and dissolved organic phosphorus: DOP) in samples of soil water collected in 2002 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). 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. 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 bi-weekly, in 2002 at the 23.10.2002; 05.11.2002; 20.11.2002; 05.12.2002; and 28.12.2002, and analyzed for dissolved inorganic P (PO4P) and total dissolved phosphorus (TDP).
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. Total dissolved P in soil solution was analyzed by irradiation with UV and oxidation with K2S2O8 followed by reaction with ammonium molybdate (Skalar catnr. 503-553w/r). 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). Dissolved organic P (DOP) in soil solution was calculated as the difference between TDP and PO4P. In a low number of samples, TDP was equal to or smaller than PO4P; in these cases, DOP was assumed to be zero.

本数据集包含2002年从大型草原生物多样性实验（耶拿实验（Jena Experiment）；详见下文）的主实验样地采集的土壤水样中的溶解磷含量测定数据，其中指标包括总溶解磷（total dissolved phosphorus: TDP）、无机溶解磷（dissolved inorganic phosphorus: PO4P）与有机溶解磷（dissolved organic phosphorus: DOP）。
该主实验共设置82块20×20米的草原样地，所用植物种质池包含隶属于4个功能群（禾草、豆科植物、高大草本与矮小草本）的60个物种。2002年5月，从该物种池中选取不同数量的植物物种播种至各样地，以构建植物物种丰富度（1、2、4、8、16与60种）与功能群丰富度（1、2、3、4个功能群）的梯度样地。样地通过每年两次除草与刈割进行维护。
2002年4月，在10、20、30与60厘米深度处安装直径12厘米、厚度1厘米、孔径1~1.6μm的玻璃吸力采样板（UMS GmbH，德国慕尼黑），用于采集土壤溶液。通过手动测量土壤基质势来调控真空系统，采样瓶持续抽至50~350 mbar的负压，使吸力压力较实际土壤水张力高约50 mbar，仅收集土壤渗滤液。2002年每两周采集一次累积土壤溶液，采样日期为2002年10月23日、2002年11月5日、2002年11月20日、2002年12月5日与2002年12月28日，随后对其中的无机溶解磷与总溶解磷进行分析。
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公司，荷兰布雷达）通过光度法测定：在酒石酸锑钾催化下，钼酸铵在酸性介质中与磷酸盐反应生成磷钼酸络合物，抗坏血酸将该络合物还原为深蓝色络合物。土壤溶液中的总溶解磷则通过紫外辐照与过硫酸钾（K₂S₂O₈）氧化后，再与钼酸铵反应进行分析（Skalar货号：503-553w/r）。
由于钼络合物仅在强酸性条件下形成，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；此外，钼酸盐反应对缩合磷酸盐不敏感。总溶解磷与无机溶解磷的检出限均为0.02 mg P·l⁻¹（CFA，Skalar）。土壤溶液中的有机溶解磷通过总溶解磷与无机溶解磷的差值计算得到。在少量样品中，总溶解磷等于或低于无机溶解磷，此类情况下有机溶解磷被赋值为0。