Saven Thai

The composition of soil organic matter is considered to have a key influence on C sequestration and global climate change and can be associated with changes in vegetation cover in the terrestrial ecosystem. Our study aimed to evaluate the soil chemical structures and various organic components from available or reactive to more stable forms in forest soils affected by acidification and after conversion from fairly close to natural beech (Fagus sylvatica) stands to a spruce (Picea abies) monoculture. Our results revealed that the beech stands had higher contents of dissolved organic carbon and low molecular mass organic acid compared to the spruce stands. The aliphatic CH groups within the soluble alkaline-extractable organic substance (AEOS) gradually disappeared with deeper soil horizons under both forest species, while the presence of aliphatic CH groups in the low-solubility AEOS was more pronounced in the A horizon under spruce and relatively increased with depth under beech stands. The carboxylic groups were more prevalent in deeper soil horizons, while polysaccharide chains and nitrogen functional groups decreased with depth under both forest stands but were more prevalent under beech than under spruce stands. These findings suggest that the stability of organic matter through the forest soil profiles increased due to the transformation of various organic compounds from litter to more stable organic matter with higher amounts of lignin components to greater amounts of carboxylic groups and aromatic groups in deeper soil horizons. Furthermore, a higher number of mobile components of soil organic matter and carboxylic acids, together with lower pH and cation exchange capacity under spruce, resulted in the leaching of nutrients, releasing risk elements into the soil solution and accelerating the podzolization process.

The study aimed to investigate the temporal changes of pH, sorption complex, and structure of soil organic matter through the forest soil profile under beech and spruce forests located in Jizera mountains (Czech Republic) and affected by natural and anthropogenic acidification. Soil samples were collected in four different years (2008, 2013, 2015, and 2020) in each horizon: fermented horizons (F), humified horizons (H), organo-mineral horizons (A), and subsurface mineral horizons (B) (cambic or spodic). The cation exchange capacity (CEC), base saturation (BS), exchangeable element contents, pH, and soil organic carbon content (SOC) were determined. The infrared soil spectra were used to calculate indices of potential wettability, aromaticity, and decomposition. Our results showed that most nutrients and aliphatic compounds were retained in the uppermost soil layers. The aromaticity of organic matter increased with depth, while polysaccharides, regarding the decomposition compound, disappeared through the soil horizons. In a long-term observation, SOC content had constantly increased under beech, while spruce remained stable in the organic horizons. Exchangeable element contents increased in each horizon, except for Al and Fe; their content quickly decreased in F horizons and slowly decreased in H horizon under both forest tree species, while the deeper horizons remained constant, but increased in A horizon under spruce. Continuously increasing base cations concentrations in sorption complex of both forest tree species during the study period revealed the effect of forest stand types on acid deposition reduction and mitigation. The temporal changes in CEC, BS, SOC, and soil wettability are more intensive in beech than in spruce forest floor.

Soil organic matter (SOM) plays vital importance for biological, chemical, and physical soil improvement and productivity. Organic matter composition also depends on different types of vegetation covers. Thus the study was aimed to estimate and characterize the soil organic matter (SOM) under different land uses (cropland, grassland, and forestland) and depths (0-10 cm, 10-20 cm, and 20-30 cm) in Prague Suchdol. Ninety samples of disturbed soil were collected within different land uses and within different depths. The soil organic matter (SOM) composition was assessed by diffuse reflectance infrared fourier transform spectroscopy (DRIFT). Humic and fulvic acid were extracted from soils and their composition was also assessed by DRIFT. Additionally, dissolved organic carbon (DOC), humus quality as ratio between absorbances of soil extract with sodium pyrophosphate at the wavelengths 400 and 600 nm, soil organic carbon (by the rapid dichromate oxidation technique), were determined on the samples as well as physical characteristics as bulk density. The data were analysed statistically by statistical package for the social sciences (SPSS) version 20. The results indicated that pHKCl is significantly different among land uses. Cropland had the highest values of pHKCl with a range from 7.76 to 6.86, followed by grassland with a range from 5.72 to 5.93 and forestland with 3.34 to 3.65, respectively. However, the humus quality was significantly different for all depths where forestland had the lowest humus quality compared to grassland and cropland, respectively. The soil organic carbon deviates statistically in depth 0-10 cm and 20-30 cm, while the depth in between from 10 to 20 cm showed no substantial difference among the land uses. Nonetheless, the result revealed that the largest differences of the spectra in the composition of organic matter were observed in the upper parts of the soil profile. The forest soil spectra had more intense aliphatic bands, carboxylic, and CH bands than spectra of grassland and cropland soils. The difference of HAs spectra was at 3 010 to 2 800 cm-1 where the most intensive aliphatic bands were in forest soil HAs, followed by grassland and cropland soil HAs. The grassland topsoil FAs spectrum differs most from the other land uses. It has lower peaks around 1 660–1 600 cm-1 and 1 200 cm-1 than cropland and forest. The concentration of low molecular mass organic acid (LMMOA) was the highest in the forest soil and the most abundant acid was citrate.