# Organic Matter Structural Composition of Vascular Epiphytic Suspended Soils of South Vietnam
## 3 Results and Discussion
### Elemental Composition  
Data of the elemental analyses and composition of the organic materials and humic substances are presented in Table 3. In general, the humic acids contain more nitrogen and hydrogen but less oxygen and carbon. Although we are comparing sets of organic precursors with group of HAs, it is evident that the differences are significant for C (F = 8.95, \(p\) < 0.0006), H (F = 8.90, \(p\) < 0.0006), N (F = 292.70, \(p\) < 0.0001) and O (F = 7.50, \(p\) < 0.002). This may be interpreted as the result of the deep transformation of organic matter during humification. This is quite important for understanding the that fact that humification appears in suspended soils and could be considered as a universal process. In addition, characterising the structural and chemical composition of the suspended soils should be noted along with the content of trace elements and metal ions. Thus, the content of mobile \(p\) varied from 267 to 691 mg/kg, mobile K 1091-4650 mg kg\({}^{-1}\), exchangeable Mg < 0.20-52.5 mmol 100 g\({}^{-1}\), exchangeable Ca 11.2-58. 8 mmo 100 g\({}^{-1}\), bulk Cu 1.62-17.6 mg kg\({}^{-1}\), Pb 1.59-11.5 mg kg\({}^{-1}\), Zn 12.8-89 mg kg\({}^{-1}\), Ni 0.97-54.2 mg kg\({}^{-1}\) and Cd < 0.005-0.105 mg kg\({}^{-1}\) (unpublished data). This suggests that the organic matter of suspended soils has strong buffer properties and can deposit ions of macronutrients, trace elements and heavy metals, which are most likely preserved in the form of complex complexes that apparently prevents their leaching. This is a fundamental point, as suspended soils are capable of retaining large masses of water due to their moisture capacity [5] and otherwise, given the vertical localization of suspended soils on the tree trunk, would be actively destroyed by water flows and washouts along the tree trunk. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & **C, \%** & **N, \%** & **H, \%** & **O, \%** & **C/N** & **H/C** & **O/C** \\ \hline
1-1 & 51.02 \({}^{*}\) \(\pm\) 0.05 & 0.84 \(\pm\) 0.0  
The representation of atomic ratios is given in Figure 5. It is evident from Figure 5 that the group of humic substances is more homogenous in comparison with the initial organic matter of both sample sets. At the same time, the initial organic matter is characterized by a wide range of atomic ratios, which is quite logical since humification leads to the selection of thermodynamically stable molecules; in the course of this process their elemental composition is homogenized. This well corresponds with theory of humificiation from [PERSON]. [PERSON] [20] and analysis of data on humic substance content provided by [25; 26; 27]. Data on structural composition of organic matter and humic acids provided in Figure 6 and in Table 4. A set of structural fragments has been identified by CP/MAS 13C NMR spectroscopy: carboxyl groups (-COOR), carbonyl fragments (-C=O), CH3-, CH2-, CH-aliphatic carbon species, -C-OR of alcohols, esters and carbohydrates as well as phenolic carbon groups (Ar-OH), quinone (Ar=O) and aromatic (Ar-) groups, which demonstrates high heterogeneity and complexity of initial organic matters and of HAs isolated from various initial organic materials. The presence of the mentioned structural fragments in both initial organic materials and humic acids demonstrates the unity of the structural composition of all organic matter of epiphytic suspended soils. Seven chemical groups in organic matter were identified by 13C-NMR spectroscopy in initial organic materials and HAs: nonpolar alkyl (0-46 ppm), N-alkyl/methoxy (46-60 ppm), O-alkyl and another carbon compounds (60-110 ppm), C, H-substituted aromatic fragments (110-144 ppm), O, N -substituted aromatic fragments (144-160 ppm), carboxyl, esters, amides (160-185 ppm) and quinones (185-200 ppm) [18]. In general, the key difference of the HAs from initial organic materials is the increased portion of aromatic carbon species and a higher ratio of aryl compounds to aliphatic ones.