# Organic Matter Structural Composition of Vascular Epiphytic Suspended Soils of South Vietnam
## 3 Results and Discussion
### Elemental Composition
This is the first attribute of the humification process [25; 26], which appears not only in \"normal\" terrestrial mineral soils but also in suspended soils of tropical ecosystems. Data obtained confirms previously published data about initial humification in suspended soils [27]. The aromaticity degree varied from 31 to 42% in humic acids and from 7 to 25% in initial organic materials. This corresponds well with the classical theory of humification [21; 28] and does not oppose the theory of \"contentious nature of soil organic matter\" [29]. Thus, continual transformation of soil organic matter and formation of the hum  
Figure 5: Van Krevelen diagram of the humic substances and organic materials. mic acids is the last point of this process. The portion of the sum of the aliphatic group was lower in humic acids (58-69%) than in initial organic materials (75-93%). This indicates that there is decreasing of the aliphatic part of organic matter under the process of suspended soil formation and humification. The quinone groups demonstrate essential decreasing in humic acids. The same may be fixed for O-alkyl and anomer carbon compounds. On the other hand, the group of nonpolar alkyl (0-46 ppm) increased in humic acids in comparison with the initial organic material. Moreover, the above-mentioned differences are evident from the shape of 13-C NMR spectra given in Figure 4. Here, there is a shift from the aliphatic maximum dominance in the case of bulk initial organic matter to the aromatic part in humic materials isolated from suspended soils. 13-C NMR spectra of suspended soils are comparable with those isolated from topsoils of Podzols of the western European plain [16] and Luvisols of the Privolzhskaya Upland [30]. In the case of a blind experiment, if the origin of humic acids is not known, they can be identified as humic substances isolated from podzolic soils (Podzols, Luvisols (Retiols). The content of C, H-substituted aromatic fragments was essentially higher than the group of O, N-substituted aromatic fragments in both humic acids and initial organic materials, which corresponds well with data on forest soils [17]. The structural composition of bulk organic matter derived from spectroscopic data is similar to very low humidified materials from normal terrestrial soils of temperate or subarctic soils [31; 32]. Thus, we can conclude, that suspended soils can serve as normal terrestrial soil in terms of litter fall material conversion. This conversion expressed in humification what may be considered as a universal mechanism for natural biotechnology--transformation and stabilization of organic matter in suspended soils of the tropical rain forest. Moreover, organic matter stabilization process take place not only in soil forest floor [33] but also on the various levels of epiphytic tropical vegetation communities. Suspended soils of the tropical forest may be considered as a very promising object of current so-called \"humiconic science\" [34]. In addition, this work provides an essential contribution to the estimation of carbon turnover rate and soil stocks in the concept of \"biotic turnover\" [35], in which the suspended parts were underestimated for many years. Additionally, in some sense, the study leads the science of humus beyond the limits of traditional soils because organic matter is accumulated and transformed not only in full-profile soils but also in soil biofilms [36] on the surface of glaciers [37], in waters [38] and, as our data showed, in suspended soils \"separated\" from the classical soil cover. The next step should be focused on investigation of 2-dimensional NMR spectra of humic acids and humification precursors, such as was performed for soils of unique ecosystems of tailgrass temperate rainforest in western Siberia [39].