This data set contains measurements of morphological root parameters, i.e. length and diameter of newly built roots. Data presented here is 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). Since 2010, plots were weeded three times per year.In June 2003, five soil cores with a 4.8 cm diameter per plot were taken to 30 cm depth. The removed soil was replaced by root-free soil from the field site. In September 2003, the initially root-free ingrowth cores were removed and the holes were refilled with root-free soil until the following withdrawal in July 2004. To extract the newly formed roots, each ingrowth core was first weighed and carefully homogenized. A subsample of 50 g of soil was suspended in water and rinsed over a 0.5 mm screen. Roots collected in the screen were transferred into a water-filled clear acrylic tray and scanned. Total root length and mean diameter were determined by using WinRhizo (Regent Instruments, Quebec, Canada). Afterwards, root length density (cm root length per cm3 soil volume) was calculated.
The Main experiment on the field site of the Jena Experiment comprises a split-plot design in which additional treatments (e.g. no weeding allowing for invasion of other species, or application of fertilizer) have been applied to subplots along the outer margin of the plots (see Treatment description in the section "further details"). While in this dataset only data from the core area (mown and weeding of all none-sown species twice a year, no additional treatments) is reported, all potential treatments are listed as the first parameters in the data file to guarantee compatibility with other datasets that include different treatments. 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 could thus not be measured. For example, in the columns of species-specific biomass cells are left blank, when the species was not sown into the respective plot. Missing values that resulted from methodological problems, sampling errors, or lost samples/data are marked with "-9999".This dataset is part of a collection of measurements of belowground plant biomass and morphological root parameters in the Jena Experiment. Similar data from other experiments (e.g. Main Experiment, Dominance Experiment; see details above), other years, or other methods quantifying related data might be available (https://doi.pangaea.de/10.1594/PANGAEA.880330).
