# Organic Matter Structural Composition of Vascular Epiphytic Suspended Soils of South Vietnam
## 2 Materials and Methods
### Laboratory Analysis  
Solid-state 13C-NMR spectra of the bulk organic matter and humic acids solid powders were measured with a Bruker Avance 500 NMR spectrometer in a 3,2-mm ZrO\({}_{2}\) rotor. The magic angle spinning speed was 20 kHz in all cases and the nutation frequency for cross polarization was u1/2p 1/4 62.5 kHz. Repetition delay and the number of scans were 3 s. Humic acids (HAs) were extracted from each sample according to a published IHSS protocol [[http://humic-substances.org/isolation-of-ihss-samples/](http://humic-substances.org/isolation-of-ihss-samples/)]([http://humic-substances.org/isolation-of-ihss-samples/](http://humic-substances.org/isolation-of-ihss-samples/)), accessed on 1 March 2022). Briefly, the soil samples were treated with 0.1 M NaOH (soil/solution mass ratio of 1:10) under nitrogen gas. After 24 h of shaking, the alkaline supernatant was separated from the soil residue by centrifugation at 1516\(\times\)\(g\) for 20 min and then acidified to pH 1 with 6 M HCl to precipitate the HAs. The supernatant, which contained fulvic acids, was separated from the precipitate by centrifugation at 1516\(\times\)\(g\) for 15 min. The HAs were then dissolved in 0.1 M NaOH and shaken for four hours under nitrogen gas before the suspended solids  
Figure 2: Some epiphytic communities and epiphytes from which suspended soils were collected: (**a**) _Lyonia caulfolia_ tree in np Bidup Nui Ba from which suspended soils were collected from heights up to 2 m, mainly under mosses and ferns; 2–4 m. moss cushions with ferns and small orchids underplanted; 4–6 m, mainly large orchids and heather and 6–8 m, mainly small orchids and lichens on individual thin branches; (**b**) moss cushions with suspended soils form in the mountain forest of np Bidup Nui Ba; (**c**) classical nesting epiphyte _Aspelium nidus_ forms suspended soils in a lowland forest (Cat Tien park); (**d**) staple epiphyte _Aglaomorpha_ sp. in mountain forest of Bidup Nui Ba; (**e**) staple epiphyte _Drynaria quecifolia_ in lowland forest (Cat Tien park); (**f**) nesting epiphyte _Hatychium bussigonium_ in lowland forest (Cat Tien) and (**g**) nesting epiphyte _Cympidium funlaysonium_ in a sparse community (Phu Quoc). were removed by centrifugation. The resulting supernatant was acidified again with 6 M HCl to pH 1 and the HAs were again isolated by centrifugation and demineralized by shaking overnight in 0.1 M HCl/0.3 M HF (soil/solution ratio of 1:1). Next, the samples were repeatedly washed with deionized water until pH 3 was reached and then finally they were freeze-dried. Data were corrected for water and ash content. The elemental composition of HAs is the percentage content of the elements C, H, N and O. For the graphical analysis of the elemental composition, we used the van Krevelen diagram [19], using H/C-O/C ratios to determine the direction of transformation processes of various organic compounds in natural conditions. The elemental composition was corrected for the weight of moisture and ash content. The oxygen content was calculated from the difference in mass of the whole samples and gravimetric concentrations of C, N, H and ash. Determination was performed with use of an elemental analyser (EA3028-HT Euro Vector, Pravia PV, Italy). The oxygen content was determined by the difference in the ratios. Gravimetric concentrations are given for C, H, O and N content. C/N, H/C, O/C and H/C were calculated from the mole fractions of C, H, O and N gravimetric contents. H/C (mod) is the number of substituted hydrogen atoms in HAs; H/C (mod) = H/C + 2(O/C) \(\times\) 0.67; the W index is the degree of oxidation in molecules [20]. SD \(\pm\) 0.05 was employed for the contents of C, H and N.  
Thin sections (0.03 mm) for micro morphological studies were prepared using the regular grinding wheel and fine (0.8-1.6 microns) abrasive paste from the micromonoliths of soils sampled during several field campaigns. Samples were air-dried and then saturated with epoxy resin.