Artificial light at night (ALAN) decreases plant diversity and performance in experimental grassland communities – Data on species biomass and traits

Artificial light at night (ALAN) affects many areas of the world and is increasing globally. To date, there has been limited and inconsistent evidence regarding the consequences of ALAN on plant communities as well as the fitness of their constituent species. ALAN could be beneficial for plants as they need light as an energy source, but they also need darkness for regeneration and growth. We created model communities composed of 16 plant species sown, exposed to a gradient of ALAN ranging from ‘moonlight only’ to conditions like situations typically found directly underneath a streetlamp. We measured plant community composition and its production (biomass), as well as functional traits of three plant species from different functional groups (grasses, herbs, legumes) in two separate harvests. We found that biomass was reduced by 33% in the highest ALAN treatment compared to the control, Shannon diversity decreased by 43% and Evenness by 34% in the first harvest. Some species failed to e..., The EcoUnits were filled with 1.23 m3 of unsterilised, well-mixed soil from the vicinity of the EcoTron, as we also monitored soil communities in the same experimental setup (see Cesarz et al.). Plant communities comprising 16 plant species were sown into soil on 19 February 2020 (see Table S1). Because the soil was not sterilised, some of the local seed bank was also transferred into our experiment. Plant communities were harvested by clipping aboveground plant biomass (2 cm above topsoil) on June 11, July 3, and August 28 (establishment period), as well as on October 27 and December 8 (measurement period). This harvest regime mimics typical intensive grassland management in central Europe, with short growth phases in between harvest events. 
For this study, we analysed the last two harvests in detail to address temporal variations and accumulated effects of the ALAN treatment (see Table S1; hereafter referred to harvest 1 and 2, respectively). The harvests differed in length: harvest ..., , # Artificial light at night (ALAN) decreases plant diversity and performance in experimental grassland communities – Data on species biomass and traits

[https://doi.org/10.5061/dryad.hhmgqnknt](https://doi.org/10.5061/dryad.hhmgqnknt)

In ALAN\_specis\_biomass.csv, Biomass per species in the proportion sorted is given. In ALAN\_biomass.csv, the biomass of the entire Ecotron is given. In ALAN\_traits.csv, traits of the species are given.

## Description of the data and file structure

ALAN\_specis\_biomass.csv:
The species are abbreviated by 3 letters genus and species. unit describes the name of the EcoUnit (numbered consecutively), light refers to the light regime (given in lux), mass indicates the biomass (in g dry matter) and harvest denotes whether it was the first or 2nd harvest studied (categorical information).

ALAN\_biomass.csv:
biomass refers to biomass (g dry matter), unit describes the name of the EcoUnit (numbered consecutively), and harvest denotes whether it was the firs...