Pellet die

A pellet die (Specac Ltd., Orpington, UK) of 13 mm diameter and a universal material testing machine with a 100 kN load cell (Instron 1175, Norwood, MA, USA) were used to manufacture the tablets. Before compression, a thin layer of magnesium stearate powder was carefully brushed onto the die wall to reduce to the friction between the powder and the die wall during compression. Approximately 700 mg powder was weighed and manually filled into the die. The direct compression method was applied to produce the tablets using flat faced punches. During compression, 60 s was set to reach maximum loads at a constant compression rate followed by 30 s for unloading. The tablet ejection speed was controlled at 2 mm/s. At each experimental condition, three repetitions were performed. The relative humidity and temperature were about 45% and 21 °C for all experiments reported here. During compression, the applied loads and the punch movement were automatically recorded using a control system. The compression data was used to plot the stress-strain profile and to assess powder compression behaviour. To produce the tablets with various solid fractions, different compression pressures (i.e., 15, 68, 90, 120, 170, 210, 260, 300, and 340 MPa) were applied.

In summer 2018, 24 shoot samples were collected from plants of three species from the Schlöppnerbrunnen fen, the same site at which the plants for the growing experiment were taken. These species were Carex rostrata, Eriophorum vaginatum and Molinia caerulea Moench. The shoots were frozen and subsequently freeze dried (Christ Alpha 1-4 LDplus, Osterode am Harz, Germany).
The plants were milled according to the procedure described in Section 4.1.4. Milled samples were subjected to an FTIR analysis (as described in Section 4.1.6) and total element mass fractions were determined with X-ray fluorescence spectroscopy at the University of Münster, Germany. For the latter, a wavelength dispersive X-ray fluorescence spectrometer (WD-XRF Rigaku ZSX Primus II, Tokyo, Japan) was used. Therefore, 500 mg of the sample was formed into a pellet at a load of 6–7 t using a pellet die (Specac, Orpington, UK), and pellets were stored in polyethylene bags in a desiccator until measurement.