Chen, Hongmei; Elle, Oliver; Weigelt, Alexandra; Mommer, Liesje; Richter, Ronny (2018): Fine root lignin content from different plots of the Jena Experiment [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.895499,

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In supplement to: Elle, Oliver; Richter, Ronny; Vohland, Michael; Weigelt, Alexandra (2019): Fine root lignin content is well predictable with near-infrared spectroscopy. Scientific Reports, 9(1), 6396, https://doi.org/10.1038/s41598-019-42837-z

Dried root samples were ground with a vibratory ball mill (MM 400, Retsch Technology GmbH, Germany). For liquid-solid pre-extraction we extracted up to 50 mg of sample with 12 mL solvent (acetone: ethanol: water; 5:3:2 volume) at 70°C for 150 minutes, turning the tubes regularly. The extracted samples were centrifuged and washed three times before drying (70°C, 48 hours). For lignin extraction, we used the acetyl bromide (AcBr) extraction as described by Iiyama & Wallis (1988), but avoided to use 70% perchloric acid that causes the formation of hydrobromic acid and unwanted acid catalyzed, chromophor-forming oxidation of polysaccharides. In brief, we extracted 10 mg sample with 5 mL 25% (vol:vol) solution of AcBr in glacial acetic acid and heated the vials in an oil bath (70°C, 60 min) with regular shaking to promote sample digestion. We chilled samples on ice (15 min), equilibrated to room temperature (30 min) and centrifuged. To mask strongly absorbing polybromide anions, 1 mL of the supernatant was diluted in 1 mL of 2N NaOH and 8 mL glacial acetic acid. We included microcrystalline cellulose (Sigma-Aldrich, USA) as control. Finally, we measured 3 mL of the sample solution at 280 nm in a spectrophotometer (Jasco V730, Jasco Labor- u. Datentechnik GmbH, Germany) to determine the specific absorption coefficients (SAC): SAC=((ODS-ODB )*F)/Wd*ml*cm^(-1)*mg^(-1); where ODS = optical density of the sample, ODB = optical density of the blank, Wd = weight of the sample and F [mL mg- 1] = dilution factor (= 50) and d [cm] = diameter of the quartz cuvette. In addition, we purified and isolated reference samples. For the calibration curve we diluted 10-750 µL extracted lignin aliquots in 8 mL masking solution, made up to 10 mL with blank solution (25% AcBr in acetic acid) and measured at 280 nm as detailed above. The lignin content (L) of all samples was calculated using regression equation: L=((SAC-0,05)*100)/13,06*%