This data set contains measurements of dissolved organic carbon 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 mm (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 dissolved organic carbon concentration by a high TOC elemental analyzer (Elementar Analysensysteme GmbH, Hanau, Germany). Samples were analyzed as soon as possible and stored at 4°C if necessary. Often in summer, no free soil solution was available for collection, especially in the upper soil layers. Annual mean values of measured biweekly concentrations of dissolved organic carbon are provided.

During summer month soil frequently dries out so that no soil pore water can be collected. Consequently, in these periods no DOC concentrations can be determined and these periods do not contribute to the reported annual means of DOC concentrations. Only in block 2 suction plates were installed in all four depth layers. Suction plates in 30 centimeter depth were installed in block 1, 2, and 3 in 2002. In 2005, additional suctions plates were installed in 20 centimeter depth in block 1, 2, and 3. In block 4, no samples are available because no plates were installed.There are two types of missing values contained in the dataset. Empty cells represent missing values that result from the design of the experiment when the respective value does not occur and thus cannot be measured. Missing values that resulted from methodological problems, sampling errors, or lost samples/data are marked with "-9999".In addition to measurement of dissolved organic carbon in soil solution, measurements of soil carbon (organic, inorganic, and total) determined from dried soil samples are available.This datasets is part of a time series of soil carbon measurements in the Main Experiment since 2002 (doi:10.1594/PANGAEA.848946).