DOI: 10.71615/bexis.31852
title: Nitrogen and carbon concentrations in aboveground biomass of seedlings as obtained in a microcosm experiment under ambient light and temperature conditions for 227 species occurring on the grassland EPs of the Biodiversity Exploratories

description: During the last two decades, the research on plant functional traits has advanced rapidly. However, so far, research has focused on traits of adult plants, while research on seedling traits is scarce. Seedling traits, however, could play an important role during plant establishment from seeds and they are essential to understand the full plant life cycle. We analyzed the nitrogen and carbon concentrations of the aboveground biomass of seedling in the stage when they had developed the first two true leaves. For this, we examined 227 temperate grassland species in a microcosm experiment under ambient light and temperature conditions in an open greenhouse at the Experimental Field Station Bad Lauchstädt (UFZ, Helmholtz Centre for Environmental Research) between 2020 and 2022. The microcosm experiment was part of the project SeedDiv within the framework of the DFG-funded joint project Biodiversity Exploratories (https://www.biodiversity-exploratories.de).
description: Species were selected from the species inventories of the grassland experimental plots of the Biodiversity Exploratories (EPs) including all species, that occurred between 2008 and 2019 on more than three plots irrespective of their cover abundances or on fewer plots with a cover-abundance &gt;1% resulting in 233 species. When possible, seeds were bought commercially from local suppliers preferentially from provenances in or close to the Exploratory regions. Seeds of some species, where it was not possible to buy seeds, we collected ourselves in the summer of 2020. (For seed sources see dataset ID 31927). Seeds were stored at room temperature (at approx. 22°C) until they were prepared for the experiment. The microcosm experiment was carried out in a greenhouse with open windows and a glass roof that closes during rain at the field station of the Helmholtz Centre for Environmental Research, UFZ in Bad Lauchstädt (51.3923°,11.8759°, 117 m a.s.l.). The experiment was sown between the 16th and 24th of November 2020. Sowing in late autumn guaranteed cold stratification and/or short days, which are necessary for several species to induce germination. All species were sown in trays (QuickPot Standard QP® 96T; HerkuPlast, Kubern GmbH) with 96 cells of 3.8 x 3.8 cm size and 7.8 cm depth, which were arranged in 6 rows each with 12 cells on each tray. The experiment consisted of two blocks, and in both blocks, each species was sown in 6 consecutive cells with 2-4 seeds per cell. The position of each species was randomly assigned in both blocks. Seedlings of some species were heavily affected by frost in late February 2021. Therefore, we re-sow these species on 2nd March 2021. Moreover, a couple of species failed to germinate in the first year or we received the seed material too late. These species were sown again with new seed material in 2021. Species were sown on 9th November 2021. For re-sowing, we used the same substratum (see below) and followed the same procedure during sowing. In addition, all species were separately sown with 50 seeds in pots of 11 x 11 cm size (12 cm depth) with five replicates per species resulting in ca. 1165 microcosms. The pots were arranged in five blocks each with one replicate per species. A few species, with only a few seeds available, could only be sown in the trays and not in pots. Pots and trays were filled with commercial potting substrate (Fruhstorfer Erde®, Type P70, Industrie-Erdenwerke Archut GmbH, Lauterbach, Germany) mixed with 25 vol% mineral sand. The mixture contained 66.35 mg kg⁻¹ plant-available phosphorus, and 283.80 mg kg⁻¹ plant-available potassium (both determined with the CAL method). Soil carbon concentration was 65.2 mg g-1, and total soil nitrogen concentration was 1.3 mg g-1. The pH (measured in a CaCl2 solution) was 7.0. Seeds were gently pressed on the soil surface and covered with a thin layer of mineral sand to avoid loss through wind. Pots and trays were watered regularly as needed. | Sampling design: Seedlings (mainly from trays) were harvested once the first two true leaves or leaf pairs (in case of species with opposite leaves) were fully expanded. In addition to the seedlings, for which we measured traits at individual seedlings (dataset ID 31830), we harvested further seedlings in the trays and pots to get enough material for chemical analysis (dataset ID 31834). In total, we could study the seedlings of 227 out of 233 sown species. | Sample preparation: All plant material was dried at 70°C for 48 hours. | Sample analysis: Seedlings per species were pooled and milled with a ball mill (MM200, Retsch) to get a homogeneous fine powder. Approx. 10 mg of the material was weighed into tin capsules and analyzed with an Elemental Analyzer (vario EL cube, Elementar Analysensysteme GmbH, Langenselbold, Germany) for carbon and nitrogen concentrations. | Equipment: ball mill (MM200, Retsch), Elemental Analyzer (vario EL cube, Elementar Analysensysteme GmbH, Langenselbold, Germany) | Data preparation: The data set does contain the values of all measurements after checking the raw data for plausibility.