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Batch experiments and XAD resin were used to investigate the adsorption of dissolved organic matter (DOM) by ferrallitic soils. The effects of soil properties and DOM characteristics on the adsorption were also studied to reveal the adsorption mechanism. The results showed that; (1) ferrallitic soils were high in DOM adsorption capacity, which increased with initial DOM concentrations, and the kinetics of DOM adsorption in the ferrallitic soils can be divided into the two stages; fast and slow reactions, it could be better fitted by first-order model; (2) the adsorption isotherms of DOM on ferrallitic soils could be better fitted by Freundlich equation, indicating the adsorption process was a physical multilayer adsorption process; (3) for different soils, the adsorption capacity of DOM was listed as follows; rhodic ferralsol > haplic ferralsol > paddy soil, for example, adsorbing capacity of compost DOM was up to 594.906, 309.317 and 206.316 mg/kg in the initial concentration of 50 mg/L, positively correlated with CEC, free iron oxide, free aluminium oxide and clay content, while negatively correlated with sand content; (4) for different DOMs, higher hydrophobic DOM had the larger adsorption capacity, which listed as follows: compost DOM (H-DOM) > soil DOM (M-DOM) > straw DOM (L-DOM); (5) for different DOM components, the adsorption capacity decreased as follows; hydrophobic neutrals (HON) > acid-insoluble matter (AIM) > hydrophobic bases (HOB) > hydrophobic acids (HOA) > hydrophillic matter (HIM), and the chain structure of aliphatic alkanes and higher aromaticity in DOM were the key factors influencing adsorption capacity as revealed by fourier-transform infrared spectroscopy (FT-IR); (6) the contribution to DOM adsorption by different fractions was the result of their adsorption capacities and contents. For different hydrophobic DOM, hydrophobic matter's contribution (HO) was more than HIM, up to 69.43%85.08%. For different polar fractions, H-DOM; HOA(40.24%) >HON (39.10%) >HIM(14.92%) >AIM(3.82%) >HOB(1.88%); L-DOM; HOA(33.50%) >HIM(30.57%) >HON(24.81%) >AIM(7.45%) >HOB (3.68%); (7) The presence of native DOM in soil impeded the exotic DOM adsorption by soil, especially for high hydrophobic DOM. [ABSTRACT FROM AUTHOR]

Fertilization is a critical agronomic measure for croplands in tropical regions, owing to their low fertility. However, the effects of fertilization on the quantity and chemodiversity of latosolic dissolved organic matter (DOM) in tropical regions remain largely unknown. Therefore, in this study, the variations in latosol DOM concentrations and chemodiversity induced by inorganic fertilization and the co-application of inorganic fertilization with straw return, sheep manure, biochar, and vermicompost fertilizers at a molecular level were systematically investigated using multispectral techniques and ultrahigh-resolution mass spectrometry. In line with our expectations, the results showed that combined inorganic-organic fertilization improved soil quality by increasing soil organic carbon content compared to that under inorganic fertilization. However, as the most active and bioavailable organic carbon pool, dissolved organic carbonconcentrations between the fertilization treatments were not significantly different (p = 0.07). However, the dissolved organic carbon concentrations under combined inorganic-organic fertilization treatment (NPK plus straw return, 263.45 ± 37.51 mg/kg) were lower than those under inorganic fertilization treatment (282.10 ± 18.57 mg/kg). Spectral analysis showed that the DOM in the combined inorganic-organic fertilization treatments had a higher degree of humification and lower autogenetic contributions. Furthermore, Fourier transform ion cyclotron resonance mass spectrometry analysis indicated that the combined inorganic-organic fertilization increased the chemodiversity of latosolic DOM and promoted the production of large, oxidized, and stable molecules, including lignin, aromatic, and tannin compounds, which potentially benefits soil carbon sequestration in tropical regions. This study could provide a theoretical basis for elucidating on the potentially relevant ecological functions and environmental effects of DOM under fertilization regimes. [Display omitted] • Concentration of DOC in the NPKSR treatment was lower than that in the NPK treatment. • Combined inorganic-organic fertilization lowered the contribution of autogenetic DOM. • Combined inorganic-organic fertilization increased DOM humification degree. • Combined inorganic-organic fertilization promoted the production of stable molecules. [ABSTRACT FROM AUTHOR]

Forest age, a critical variable for land-use decision makers, is known to change soil microbial communities. However, how such changes affect microbial metabolic strategy and the associated soil C mineralization processes in different forest ages remains unknown, especially in tropical region. To address this issue, three different aged rubber plantations, namely 4-year-old (Young, YRP), 15-year-old (Mature, MRP), and 31-year-old (Old, ORP), were studied to reveal the soil mineralization characteristics. Furthermore, to understand the mechanism from the coupled perspective of decomposers and substrate availability, the microbial metabolic strategy was deciphered by 2D-COS-Biolog assay, and linked with soil microbial composition and labile-/recalcitrant- organic pools. Results showed that YRP was characterized by having more copiotrophic taxa (e.g., actinobacteria) and the largest G(-)/G(+) ratio and invertase activity. Thus, YRP exhibited a preferential utilization for carbohydrate and the largest SOC mineralization rate. In contrast, regardless of abundant labile C and N pools in MRP, the soil microbial communities were shifted to oligotrophic taxa in utilizing resistant polymer, and MRP contained abundant G(+), fungi and arbuscular mycorrhizal fungi related to aggregate formation. As a result, the soil mineralization rate in MRP was reduced by 66 % compared with YRP. However, the SOC mineralization rate was unchanged from MRP to ORP, primarily because the increased proportion of recalcitrant nutrient pool, and soil microorganism had greater priority in utilizing relatively resistant amine. The structural equation modeling revealed that the variations in mineralization were mainly regulated by soil microbial composition and metabolic strategy, and partially affected by soil C and N pools. Furthermore, random forest model indicated that soil pH, NH 4 -N and C/N were also the crucial factor for mineralization by affecting soil microbial communities during stand development. In summary, these findings improve our understanding in soil C budget and contribute to the C accurate management during plantation development. [Display omitted] • SOC mineralization decreased from young to mature stage and then remained unchanged. • Young plantation contained more fungi and preferentially utilized carbohydrate. • More recalcitrant pool and amine utilization caused a lower SOC mineralization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Higher labile SOC fractions in natural regeneration compared to afforestation. • Different microbial community structures in natural regeneration and afforestation. • Natural regeneration had a highly complex and stable microbial network. • Microbial communities were driven by soil C/N, available nutrient, pH, POC, and MBC. Vegetation restoration is an effective strategy for sequestering soil organic carbon (SOC) and restoring degraded ecosystems. However, the effects of different restoration strategies on SOC quantity and quality and the underlying microbial response mechanisms in a karst region of southwest China remain unclear. This study quantified soil physicochemical properties, soil labile SOC fractions (dissolved organic carbon (DOC), microbial biomass carbon (MBC), light fraction organic carbon (LFOC), coarse particulate organic carbon (CPOC), and fine particulate organic carbon (FPOC)), and the abundances, α-diversities, and compositions of bacterial and fungal communities under afforestation (Macadamia ternifolia F. Muell. and Mangifera indica L.) and natural regeneration (grassland and secondary forest), using maize field as the reference. Compared to afforestation, under natural regeneration the SOC and soil moisture content (SMC) increased by 80.3% and 21.7%, respectively, and pH decreased by 0.35, and labile SOC fractions (DOC, MBC, LFOC, CPOC, and FPOC) increased by 72.2%–172.0%, indicating that natural regeneration facilitated SOC sequestration, especially for labile SOC fractions. Phospholipid fatty acid analysis indicated that natural regeneration and afforestation significantly (p < 0.05) increased bacterial and fungal abundances and altered community compositions. Moreover, the natural regeneration co-occurrence network was more complex and stable than that of afforestation. Redundancy analysis and structural equation modeling indicated that variations in bacterial and fungal composition were primarily driven by soil C/N, available nutrient, pH, particulate organic carbon, and MBC. Overall, these findings suggest that natural regeneration is a promising restoration strategy for sequestering labile SOC and maintaining bacterial and fungal community stability. Additionally, soil properties and labile SOC fractions may coregulate microbial community changes following vegetation restoration in this karst region. [ABSTRACT FROM AUTHOR]