Changes in water‐extractable organic matter in tropical forest and agricultural soils as detected by the DRIFT spectroscopy technique

Abstract

Water-extractable organic matter (WEOM) drives many fundamental functions which determine soil equilibria, acting as a useful probe to highlight the effect of land management on overall C cycling. The ecological importance of WEOM is emphasized in tropical environments characterized by humid climate and short OC turnover. The low OC concentration and the physical-chemical conditions associated to water dissolved compounds determine an analytical issue for the characterization of WEOM.The present experiment aimed to test the diffuse reflectance infrared Fourier transformation (DRIFT) spectroscopy as a rapid tool to evaluate the dynamic of WEOM in tropical soils under different soil organic matter (SOM) managements. The influence of SOM composition on WEOM fraction was evaluated in a laboratory incubation of two tropical soils treated with different organic amendments. The superficial layers of forest and sugarcane Ultisol were incubated for 1 year with 10 mg C g À1 soil of litter from either native tropical forest or sugarcane crop residues. The sugarcane residues promoted a fast increase of dissolved organic carbon (DOC) followed by a subsequent decrease in both soils, whereas the soils amended with forest litter showed DOC dynamics similar to control samples. The DRIFT analysis unveiled changes in the chemical profile of WEOM mainly reflected on the preservation of dissolved hydrophobic compounds. The results indicate the DRIFT technique as an efficient tool to monitor the chemical changes of WEOM f as related to soil use and organic inputs, and to support a comprehensive understanding of the interaction of WEOM in agro-ecological and environmental processes.

Evaluation of Sustainable Recycled Products to Increase the Production of Nutraceutical and Antibacterial Molecules in Basil Plants by a Combined Metabolomic Approach

“…The first spectral region (0–45 ppm) includes the alkyl-C resonances, associated to the methylene segment (-CH 2 -) in aliphatic chains of various lipid compounds, such as fatty acids, plant waxes, and bio-polyesters [ 24 ]. In water dissolved fractions of CT-ART and CT-COF samples, the multiple peaks of alkyl-C interval may also indicate the presence of low molecular weight compounds such as branched acids and syderophors from plant and microbial origin [ 26 ]. The less intense shoulders within the 35–45 ppm range ( Figure 1 ), are attributable to the tertiary (CH) and quaternary (C–R) carbons in assembled rings of sterol derivatives, as well as to CH and CH 2 groups in α and β position of peptidic moieties and branched alkyl compounds [ 24 , 25 ].…”

“…The signals at 61/62 ppm represent the carbon nucleus in position 6, followed by the intense coalescence around 73 ppm formed by the overlapping resonances of carbon 2, 3, and 5, in pyranoside structures, while the most de-shielded peak at 105/6 ppm derives from the di-O-alkyl anomeric carbon in linked glucose units [ 13 , 25 ]. The lower intensity or lack of C resonances at 82 ppm associated to C4 of hexose structures tied through β 1→4 bond ( Figure 1 ), suggest the prevalence of pentose units of hemicellulose as well as the incorporation of oligosaccharides and simple carbohydrates [ 13 , 24 , 25 , 26 ]. Moreover, the high field shift of anomeric C 1 towards 101 ppm in CT samples ( Figure 1 ), further support the preferential solubilization of dissolved low molecular weight sugars not involved in the glycosidic bonds [ 25 ].…”

“…The HB, ARM and A/OA parameters are widely applied to estimate both the biochemical stability of natural organic matter, as well as the influence of structural properties on the biostimulant activities of organic extracts [ 24 , 26 ]. The lignin ratio (LigR) may be used to evaluate the relative contribution of lignin-components and that of C-N carrying moieties as well as to discriminate between signals owing to lignin and those characteristic to other phenolic compounds [ 13 , 25 ].…”

Influence of land use and different plant residues on isotopic carbon distribution of total and water extractable organic matter in an incubation experiment with weathered tropical soil

“…Furthermore, the dissolved bioactive organic compounds mediate both the soil–plant interactions within the rhizosphere (Baía et al, 2020) and the soil‐liquid phase equilibrium related to accumulation processes of soil organic carbon (SOC) (Riley et al, 2014). Since the DOM usually represents a minor fraction of the overall SOC pool (Chantigny et al, 2014; da Silva et al, 2021). , it is readily affected by land use and soil management and is hence considered a valuable probe to follow the OC cycling in both forests and cropped soils (Paul, 2016; Tong et al, 2021).…”

“…In tropical ecosystems, all the plant residues that arrive on the soil surface enter a rapid decomposition process (Fujii et al, 2020; Krull et al, 2002). The fast OC turnover and the humid climate foster the release of dissolved organic fraction and enhance the exchange between soil and water, with a determinant influence on ecological features of both the lands and catchment basins (Tadini, Constantino, et al, 2015; Tadini, Pantano, et al, 2015) as well as on both dynamics and net ecosystem carbon balance of forests and agro‐ecosystems (da Silva et al, 2021; Kindler et al, 2011).…”