S1 File -

<div><p>Peat is the main constituent of cultivation substrates and a precious non-renewable fossil material. Peatlands provide important ecosystem services and allow the absorption and storage of carbon. Protecting peatlands helps tackle climate change and contributes to biodiversity conservation. Due to its importance, it is necessary to implement strategies to reduce the use of peat, such as replacing it with biomass-based alternative growing media constituents, such as <i>Sphagnum</i> moss. In this study, we compared the metal release and binding properties at two different pH, antioxidant activity, and total phenolic content of peat and <i>Sphagnum</i> moss from the Tierra del Fuego (TdF) region of southern Patagonia. Levels of the elements were determined by inductively coupled plasma mass spectrometry (ICP-MS), while the types and amounts of functional groups were characterized and compared using Fourier transform infrared (FTIR) spectroscopy. The total phenol level and antioxidant capacity were assessed using the Folin-Ciocalteu method and 2,2-diphenyl-1-picrylhydrazyl test. There are generally higher concentrations of leachable elements in peat than in <i>Sphagnum</i> moss at pH = 2, except Cs, Rb, Ti, and Zr. In contrast, at pH = 5, levels of all leached elements are highest in <i>Sphagnum</i> moss. <i>Sphagnum</i> moss shows a higher metal adsorption capacity than peat, except for Be, Mn, Tl, and Zn. Finally, the results showed that both matrices contained similar total phenolic contents: 0.018 ± 0.011 mg gallic acid equivalent (GAE) per gram dry sample for peat and 0.020 ± 0.007 mg GAE g<sup>-1</sup> for <i>Sphagnum</i> moss. Instead, <i>Sphagnum</i> moss extracts showed a significantly higher antioxidant activity [0.026 ± 0.028 mmol Trolox equivalents (TE) g<sup>-1</sup>] than that estimated in peat (0.009 ± 0.005 mmol TE g<sup>-1</sup>). Humic acids, carboxylic acids, and phenolic and lignin groups were identified as the functional groups that mainly determined the antioxidant activity of the <i>Sphagnum</i> moss compared to peat. The present study resulted in an advancement of knowledge of these materials for more thoughtful future use and possible replacements.</p></div>