Dissolved nitrogen in soil solution of the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of dissolved nitrogen (total dissolved nitrogen: TDN, dissolved organic nitrogen: DON, dissolved ammonium: NH4+, and dissolved nitrate: NO3-) in samples of soil water collected 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. In April 2002 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 depths of 10, 20, 30 and 60 cm to collect soil solution. 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 nitrate (NO3-) and ammonium (NH4+) concentrations with a continuous flow analyzer (CFA, Skalar, Breda, The Netherlands). Nitrate was analyzed photometrically after reduction to NO2- and reaction with sulfanilamide and naphthylethylenediamine-dihydrochloride to an azo-dye. Our NO3- concentrations contained an unknown contribution of NO2- that is expected to be small. Simultaneously to the NO3- analysis, NH4+ was determined photometrically as 5-aminosalicylate after a modified Berthelot reaction. The detection limits of NO3- and NH4+ were 0.02 and 0.03 mg N L-1, respectively. Total dissolved N in soil solution was analyzed by oxidation with K2S2O8 followed by reduction to NO2- as described above for NO3-. Dissolved organic N (DON) concentrations in soil solution were calculated as the difference between TDN and the sum of mineral N (NO3- + NH4+). In 5% of the samples, TDN was equal to or smaller than mineral N. In these cases, DON was assumed to be zero.本数据集包含来自大型草原生物多样性实验（耶拿实验；详见下文）主实验样地采集的土壤水样品中溶解态氮的测定数据，涵盖总溶解态氮（total dissolved nitrogen: TDN）、溶解态有机氮（dissolved organic nitrogen: DON）、溶解态铵（dissolved ammonium: NH4+）以及溶解态硝酸盐（dissolved nitrate: NO3-）。 该主实验共设置82个20×20 m的样地，所用植物物种池包含60个物种，分属4个功能群：禾本科植物、豆科植物、高大草本与矮小草本。2002年5月，研究人员从该物种池中选取不同数量的植物物种播种于各实验样地，以构建植物物种丰富度（1、2、4、8、16及60种）与功能群丰富度（1、2、3、4个功能群）的梯度序列。样地通过每半年一次的除草与刈割进行维护。 2002年4月，研究人员安装了直径12 cm、厚度1 cm、孔径1-1.6 µm的玻璃负压采样板（UMS GmbH，德国慕尼黑），布设深度分别为10 cm、20 cm、30 cm与60 cm，用于采集土壤溶液。采样瓶持续抽至50至350 mbar的负压，使抽吸压力较实际土壤水吸力高约50 mbar，因此仅收集土壤渗滤液。 研究人员每两周采集一次累积土壤溶液样品，使用连续流动分析仪（continuous flow analyzer, CFA，Skalar，荷兰布雷达）测定硝酸盐（NO3-）与铵（NH4+）浓度。硝酸盐经还原为亚硝酸盐（NO2-）后，与磺胺及萘乙二胺二盐酸盐反应生成偶氮染料，通过光度法完成定量。本研究测定的NO3-浓度中包含未知占比的NO2-贡献，预计占比极低。与硝酸盐分析同步，经改良的伯特洛反应（Berthelot reaction）后，以5-氨基水杨酸为显色剂，通过光度法测定NH4+浓度。NO3-与NH4+的检出限分别为0.02与0.03 mg N L-1。 土壤溶液中的总溶解态氮（TDN）采用过硫酸钾（K2S2O8）氧化法消解，随后按照前述硝酸盐分析步骤还原为NO2-并完成定量。溶解态有机氮（DON）浓度通过总溶解态氮（TDN）与矿质氮（NO3- + NH4+）的差值计算得到。在5%的样品中，TDN小于或等于矿质氮浓度，此类样品的DON被认定为0。