This dataset contains community leaf area index (LAI) in the Jena-Ecotron Experiment in 2012. This experiment was conducted in the Montpellier European Ecotron (CNRS, France), an advanced controlled environment facility for ecosystem research, and aimed at understanding the impact of plant species richness (4 vs. 16 species) for ecosystem carbon and water fluxes.The soil monoliths used in this experiment contained plant communities originating from the long- term Jena Experiment (50°57.1' N, 11°37.5' E, 130 m above sea level; mean annual temperature 9.3°C, mean annual precipitation 587 mm) established in May 2002. Twelve plots were selected for the Jena-Ecotron study according to the following criteria: (1) the four functional groups grasses, legumes, small and tall herbs were present, (2) realized species numbers were close to sown species richness, and (3) plots were equally distributed across the experimental field site to account for different soil textures. Large monoliths (2 m² surface area, diameter of 1.6 m, 2 m depth with a weight of 7 to 8 tons) including intact soil and vegetation were excavated in December 2011 and placed in lysimeters. In March 2012, before the start of the vegetation growth, the lysimeters were transported and installed in the Macrocosms platform of the Montpellier European Ecotron.Community leaf area index (LAI) was measured with a portable LAI-2000 plant canopy analyzer (LI-COR, Lincoln, USA) on 15th July 2012. LAI was measured under diffuse light (evening) by taking one reference measurement above the canopy and five measurements near ground level within the center of each lysimeter. The zenith angle was restricted to 0-43° in order to minimize the edge effect (Hyer & Goetz, 2004) inherent to a canopy with a surface of 2m². In lysimeters with a high proportion of one rosulate species (Plantago media) with leaves laying very close to the ground, the values measured with the LAI-2000 were replaced with the average value of two leaf area measurements using a LI-3100 leaf area meter (LI-COR, Lincoln, USA) from two rectangles of 0.2 × 0.5 m per plot.

There are two types of missing values contained in datasets from the Jena Experiment. Empty cells represent missing values that result from the design of the experiment. Empty cells result when the respective value does not occur in the design and could thus not be measured. For example, in the case of species-specific biomass cells are left blank, when the species was not sown in 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 the Jena-Ecotron Experiment, which was part of the Jena Experiment.