Evaluation of the roles of metals and humic fractions in the podzolization of soils from the Amazon region using two analytical spectroscopy techniques

Abstract

Soil organic matter (SOM) plays an important role in environmental sustainability, since it is involved in carbon and nutrient cycling. Consequently, it is a key factor to consider in studies concerning global climate change and agronomy.Among the main components of SOM are humic substances (HS), which are divided, according to their solubility, into humic acid (HA), fulvic acid (FA), and humin (HU) fractions. Study of the chemical properties of this organic matter is important for understanding the biogeochemical processes occurring in the soil. The aim of this work was to determine the metals iron (Fe) and aluminum (Al), using flame atomic absorption spectrometry (FAAS) and laser-induced breakdown spectroscopy (LIBS), in order to elucidate the role of organic matter in the transport of these metals in Amazonian soils. The results showed that FA was important for Al, while the HA fraction was more selective towards Fe. The translocations of these metals to deeper profiles in two different soils involved either young and less humified organic matter, or older organic matter with a low degree of humification. Therefore, these two humic fractions were involved in the process of soil podzolization, with FA having a predominant role in the transport of Al, while HA was mainly responsible for the transport of Fe.

Comparison of Sample Preparation Techniques for the (−)ESI-FT-ICR-MS Analysis of Humic and Fulvic Acids

“…To analyze FA samples, Amazon-C FA was first prepared using the CE EXTRACTION approach. This approach was chosen as this white-colored sample has a high content of Al-phenol complexes or imogolite-like minerals that had survived CE and DAX-8 resin purifications . Employing the CE EXTRACTION sample preparation for both HA and FA fractions would have been ideal for achieving fully comparable data if HA and FA fractions of same soil were compared.…”

“…This approach was chosen as this white-colored sample has a high content of Al-phenol complexes or imogolite-like minerals that had survived CE and DAX-8 resin purifications. 102 Employing the CE EXTRACTION sample preparation for both HA and FA fractions would have been ideal for achieving fully comparable data if HA and FA fractions of same soil were compared. The resultant (−)ESI-FT-ICR mass spectrum was of poor quality and only 1156 peaks were detected, 792 (58%) of which were salts (Figure 3).…”

Carbon and Nitrogen Stocks and Microbiological Activity Under Forest-Pasture System and Traditional Pasture in Pernambuco

“…Humic substances are among the main components of Organic Soil Matter (OSM), playing a central role in the stabilization of Soil Organic Carbon (SOC) reservoirs and can be classified, according to their solubility, into fractions of humic acids (HA), fulvic acids (FA) and humines (HU). Since the distribution of the OSM composition is a deposit of information about the main processes that occur in the soil (Doupoux et al, 2017;Xu et al, 2018;Tadini et al, 2019).…”

Characterization of an Amazon Soil Profile by Laser-Induced Breakdown, Raman, and Fluorescence Spectroscopies

“…The spodosols below the Amazon rainforest are typically accumulating a great quantity of soil organic matter (SOM) on their surface and along their profile [3][4][5]; thus, a more extended study of them is extremely important. Laser-induced breakdown spectroscopy (LIBS) is a very versatile technique widely applied in several research areas, including the environmental sector, and offers the possibility of on-site measurements [6][7][8][9][10]. In particular, this technology can rapidly and accurately detect and identify the constituent chemical elements, i.e., provide a "chemical fingerprint" of the analyzed material, thus allowing the characterization of diverse organic and inorganic materials in real-time, requiring no sample preparation and offering high sensitivity and specificity [11].…”

“…Additionally, Raman spectroscopy is a powerful, non-destructive consolidated technique for molecular analysis [12] and is widely applied to various types of agro-environmental samples [13][14][15], also featuring a possible use for in situ analysis. Finally, fluorescence spectroscopy is a very sensitive technique widely applied for the selective study of "fluorophores" and to investigate the processes of interaction between metal ions and organic matter in soils, providing specific analysis of the structure and dynamics of macromolecules [5,6,[16][17][18][19].…”