DOI: 10.25829/bexis.31321-4
title: Biological nitrogen fixation and concentrations of nutrients and non-structural carbohydrates in deadwood of 13 different tree species

description: Deadwood is an extremely nitrogen poor plant litter whose decomposition may rely on external nitrogen sources. Biological nitrogen fixation by free-living diazotrophs is a potential pathway of nitrogen acquisition in deadwood. Still, the control of this process by tree species specific traits is hardly known.We determined rates of biological nitrogen fixation, respiration rate, and concentrations of nutrients and non-structural carbohydrates in deadwood logs of the BELongDead project from 13 tree species in the Hainich-Dün region of the Biodiversity Exploratories in June 2020. The data collection and analysis was part of the project Woodstock within the framework of the DFG-funded joint project Biodiversity Exploratories (https://www.biodiversity-exploratories.de).
description: Detailed description of study design: In winter 2008/09, freshly cut logs of 13 different tree species were placed on the forest soil in random order and within 1m distance to each other. The logs were 4m long and around 31cm in diameter. Various parameters have been measured throughout the years. For further details on the study design see: Kahl et al. 2017. In June 2020, after 12 years of decomposition, deadwood samples of the outer 7 cm of the BELongDead logs in the Hainich-Dün exploratory were taken on 9 EP plots. Bark and leaves were removed. The samples were further processed in the laboratory.<br>Sampling design: The outer 7 cm of the logs were cut laterally from the stem with an electric rip saw and chiseled out (about 2cm wide). For each of the 13 tree species per plot, one sample was taken.<br>Sample preparation: Deadwood samples were kept cool until further treatment. In the laboratory, one part of the sample was saturated with tap water for 16h before samples were drained, and acclimatized at 20°C in the dark for 5 days. Another part of the sample was frozen at -18°C until analysis of nutrients and non-structural carbohydrates.<br>Sample analysis: Biological nitrogen fixation, respiration rate and water content: Deadwood samples were weight into glass flasks, fitted with a septum and flush for 10 min with a prepared gas mixture (8% O2, 30% N and 62% He (Riessner-Gase GmbH, Lichtenfels, Germany). 25 mL of 15N2 gas was added and flasks were incubated in the dark at 20°C for 72h before drying at 60°C. Incubated and non-incubated subsamples were grinded using a ball mill (MM400, Retsch GmbH, Germany), and sent to the Centre for Stable Isotope Research and Analysis Göttingen for measuring the δ15N signature and N content. During the incubation, the respiration rate of deadwood was determined by measuring the increase in carbon dioxide concentration 21h and 45h after flushing, using a gas chromatograph (SRI 8610C, SRI instruments, Torrance, CA, USA) with a flame ionization detector coupled to a methanizer catalyst. The water content of the deadwood was determined by the wet and dry weight of the incubation samples. Non-structural carboydrates: At the Max Planck Institute of Biogeochemistry, Jena, concentrations of non-structural carbohydrates were measured. 80% ethanol was mixed with 30 mg of ground deadwood sample and heated to 90°C. After cooling down to room temperature, the mixture was centrifuged at 13,000 g for one min. The supernatant was filtered and analysed for concentrations of glucose, arabinose, xylose, galactose and total non-structural carbohydrates. Nutrient concentrations: 1 g of deadwood sample was filled in vessels and 10 mL of 65% HNO3 was added. The mixture was microwaved (MARS6, CEM), filtered (0.45µm) and analyzed at the Analytical Chemistry Lab, University Bayreuth, for Ca, Mg, K, P, S and Mn according to manufactures instructions. C concentration and CN ratio: C was analyzed with a vario Max CN element analyzer (elementar Analysensysteme GmbH, Hanau, Germany). With the concentrations of C and N, the CN ratio was calculated.<br>Equipment: electric rip saw, ball mill (MM400, Retsch GmbH, Germany), gas chromatograph (SRI 8610C, SRI instruments, Torrance, CA, USA) with a flame ionization detector (FID) coupled to a methanizer catalyst, microwave (MARS6, CEM), vario Max CN element analyzer (elementar Analysensysteme GmbH, Hanau, Germany)<br>Literature references: Kahl T, Arnstadt T, Baber K, Bässler C, Bauhus J, Borken W, Buscot F, Floren A, Heibl C, Hessenmöller D, Hofrichter M, Hoppe B, Kellner H, Krüger D, Linsenmair KE, Matzner E, Otto P, Purahong W, Seilwinder C, Schulze E-D, Wende B, Weisser WW, Gossner MM (2017) Wood decay rates of 13 temperate tree species in relation to wood properties, enzyme activities and organismic diversities. For Ecol Manage 391:86–95. https://doi.org/10.1016/j.foreco.2017.02.012