Insights into growth stages and genotypes in airborne Pb accumulation in Oryza sativa L. grains: Utilizing isotope fingerprinting alongside a model study.

Atmospheric exposure is an important pathway of accumulation of lead (Pb) in Oryza sativa L. grains. In this study, source contributions of soil, early atmospheric exposure, and late atmospheric exposure, along with their bioaccumulation ratios were examined both in the pot and field experiments using stable Pb isotope fingerprinting technology combined with a three-compartment accumulation model. Furthermore, genotype differences in airborne Pb accumulation among four field-grown rice cultivars were investigated using the partial least squares path model (PLS-PM) linking rice Pb accumulation to agronomic traits. The findings revealed that during the late growth period, the air-foliar-grain transfer of Pb was crucial for rice Pb accumulation. Approximately 69-82% of the Pb found in polished rice was contributed by atmospheric source, with more than 80% accumulating during the late growth stage. The air accumulation ratios of rice grains were genotype-specific and estimated to be 0.364-1.062 m3/g during the late growth. Notably, grain size exhibited the highest standardized total effects on the airborne Pb concentrations in the polished rice, followed by leaf Pb and the upward translocation efficiency of Pb. The present study indicates that mitigating the health risks associated with Pb in rice can be achieved by controlling atmospheric Pb levels during the late growth stage and choosing Japonica inbred varieties characterized by large grain size.

Resveratrol reverses Palmitic Acid-induced cow neutrophils apoptosis through shifting glucose metabolism into lipid metabolism via Cav-1/ CPT 1-mediated FAO enhancement.

Elevated plasma nonesterified fatty acids (NEFAs) affect neutrophils function and longevity during the periparturient period in dairy cows. Previous research has shown that resveratrol (RSV) may protect cell viability from NEFA-induced damage by regulating energy metabolism. However, it is unclear whether RSV has a protective effect on palmitic acid (PA)-treated neutrophils. The aim of this study was to investigate the molecular regulatory mechanism of the protective effect of RSV on neutrophils. The results showed that treatment with high concentrations of RSV (50 µM, 100 µM) maintained neutrophils activity by inhibiting neutrophils apoptosis (P < 0.05). Further analysis showed that high concentrations of RSV enhanced fatty acid oxidation (FAO) to produce ATP by promoting the expression of CAV1, ACSL-1 and CPT1 (P < 0. 05) while inhibiting glycolysis by suppressing PFK1 activity (P < 0. 05) and reducing glucose transport-related protein (GLUT1/GLUT4) expression by inhibiting glucose uptake (P < 0.05). These results suggest that RSV protects neutrophils from PA-induced apoptosis by regulating energy metabolism. Our results revealed that RSV protects neutrophils from PA-induced apoptosis by shifting glucose metabolism to lipid metabolism. This study tenders to a meaningful understanding of the effects of RSV on neutrophils function in periparturient cows suffering from negative energy balance (NEB).

Microbial keystone taxa drive succession of plant residue chemistry.

Managing above-ground plant carbon inputs can pave the way toward carbon neutrality and mitigating climate change. Chemical complexity of plant residues largely controls carbon sequestration. There exist conflicting opinions on whether residue chemistry diverges or converges after long-term decomposition. Moreover, whether and how microbial communities regulate residue chemistry remains unclear. This study investigated the decomposition processes and residue composition dynamics of maize straw and wheat straw and related microbiomes over a period of 9 years in three climate zones. Residue chemistry exhibited a divergent-convergent trajectory during decomposition, that is, the residue composition diverged during the 0.5-3 year period under the combined effect of straw type and climate and then converged to an array of common compounds during the 3-9 year period. Chemical divergence during the first 2-3 years was primarily driven by the changes in extracellular enzyme activity influenced by keystone taxa-guided bacterial networks, and the keystone taxa belonged to Alphaproteobacteria, particularly Rhizobiales. After 9 years, microbial assimilation became dominant, leading to chemical convergence, and fungi, particularly Chaetomium, were the main contributors to microbial assimilation. Overall, this study demonstrated that keystone taxa regulate the divergent-convergent trajectory in residue chemistry.

Dexamethasone enhances glucose uptake by SGLT1 and GLUT1 and boosts ATP generation through the PPP-TCA cycle in bovine neutrophils.

BACKGROUND: Clinical dexamethasone (DEX) treatment or stress in bovines results in extensive physiological changes with prominent hyperglycemia and neutrophils dysfunction. OBJECTIVES: To elucidate the effects of DEX treatment in vivo on cellular energy status and the underlying mechanism in circulating neutrophils. METHODS: We selected eight-month-old male bovines and injected DEX for 3 consecutive days (1 time/d). The levels of glucose, total protein (TP), total cholesterol (TC), and the proinflammatory cytokines interleukin (IL)-1ß, IL-6 and tumor necrosis factor (TNF)-α in blood were examined, and we then detected glycogen and adenosine triphosphate (ATP) content, phosphofructosekinase-1 (PFK1) and glucose-6-phosphate dehydrogenase (G6PDH) activity, glucose transporter (GLUT)1, GLUT4, sodium/glucose cotransporter (SGLT)1 and citrate synthase (CS) protein expression and autophagy levels in circulating neutrophils. RESULTS: DEX injection markedly increased blood glucose, TP and TC levels, the Ca2+/P5+ ratio and the neutrophil/lymphocyte ratio and significantly decreased blood IL-1ß, IL-6 and TNF-α levels. Particularly in neutrophils, DEX injection inhibited p65-NFκB activation and elevated glycogen and ATP contents and SGLT1, GLUT1 and GR expression while inhibiting PFK1 activity, enhancing G6PDH activity and CS expression and lowering cell autophagy levels. CONCLUSIONS: DEX induced neutrophils glucose uptake by enhancing SGLT1 and GLUT1 expression and the transformation of energy metabolism from glycolysis to pentose phosphate pathway (PPP)-tricarboxylic acid (TCA) cycle. This finding gives us a new perspective on deeper understanding of clinical anti-inflammatory effects of DEX on bovine.

Mechanism for selective binding of aromatic compounds on oxygen-rich graphene nanosheets based on molecule size/polarity matching.

Selective binding of organic compounds is the cornerstone of many important industrial and pharmaceutical applications. Here, we achieved highly selective binding of aromatic compounds in aqueous solution and gas phase by oxygen-enriched graphene oxide (GO) nanosheets via a previously unknown mechanism based on size matching and polarity matching. Oxygen-containing functional groups (predominately epoxies and hydroxyls) on the nongraphitized aliphatic carbons of the basal plane of GO formed highly polar regions that encompass graphitic regions slightly larger than the benzene ring. This facilitated size match-based interactions between small apolar compounds and the isolated aromatic region of GO, resulting in high binding selectivity relative to larger apolar compounds. The interactions between the functional group(s) of polar aromatics and the epoxy/hydroxyl groups around the isolated aromatic region of GO enhanced binding selectivity relative to similar-sized apolar aromatics. These findings provide opportunities for precision separations and molecular recognition enabled by size/polarity match-based selectivity.

Airborne lead: A vital factor influencing rice lead accumulation in China.

Traditionally, lead (Pb) in rice grains has been thought to be mostly derived from soil, and the contribution of aerosol Pb remains so far unknown. Based on a meta-analysis, we surprisingly found rice Pb content decreased proportionally with urban atmospheric Pb concentrations in major rice-growing provinces in China during 2001-2015, suggestive of the strong influence of long-range Pb transport on agricultural environment. With the combination of field survey, field experiment, as well as a predictive model, we confirmed high contribution of atmospheric exposure to rice grain Pb in China. We for the first time developed a predictive mathematical model which revealed that aerosol Pb accumulation ratios of rice grains were related to both grain weight and accumulation types. We successfully predicted the national-scale rice Pb in China on the basis of the public data of urban PM2.5 from 19 rice-growing provinces and proposed a seasonal atmospheric Pb limit of 0.20 µg m-3 based on the safe threshold level of Pb in rice, which was much lower than the current limit of 1 µg m-3 set in China.

Surface-catalyzed hydrolysis by pyrogenic carbonaceous matter and model polymers: An experimental and computational study on functional group and pore characteristics.

We employed a polymer network to understand what properties of pyrogenic carbonaceous matter (PCM; e.g., activated carbon) confer its reactivity, which we hereinafter referred to as PCM-like polymers (PLP). This approach allows us to delineate the role of functional groups and micropore characteristics using 2,4,6-trinitrotoluene (TNT) as a model contaminant. Six PLP were synthesized via cross-coupling chemistry with specific functionality (-OH, -NH2, -N(CH3)2, or -N(CH3)3+) and pore characteristics (mesopore, micropore). Results suggest that PCM functionality catalyzed the reaction by: (1) serving as a weak base (-OH, -NH2) to attack TNT, or (2) accumulating OH- near PCM surfaces (-N(CH3)3+). Additionally, TNT hydrolysis rates, pH and co-ion effects, and products were monitored. Microporous PLP accelerated TNT decay compared to its mesoporous counterpart, as further supported by molecular dynamics modeling results. We also demonstrated that quaternary ammonium-modified activated carbon enhanced TNT hydrolysis. These findings have broad implications for pollutant abatement and catalyst design.

Pyrogenic carbon-promoted haloacetic acid decarboxylation to trihalomethanes in drinking water.

Drinking water disinfection by chlorination or chloramination can result in the formation of disinfection byproducts (DBPs) such as haloacetic acids (HAAs) and trihalomethanes (THMs). Pyrogenic carbonaceous matter (PCM), such as activated carbon (AC), is commonly used as an ostensibly inert adsorbent to remove HAAs from water. HAA degradation has been mainly attributed to biological factors. This study, for the first time, revealed that abiotic HAA degradation in the presence of PCM could be important under water treatment conditions. Specifically, we observed complete destruction of Br3AA, a model HAA, in the presence of powder AC at pH 7 within 30 min. To understand the role of PCM and the reaction mechanism, we performed a systematic study using a suite of HAAs and various PCM types. We found that PCM significantly accelerated the transformation of three HAAs (Br3AA, BrCl2AA, Br2ClAA) at pH 7. Product characterization indicated an approximately 1:1 HAA molar transformation into their respective THMs following a decarboxylation pathway with PCM. The Br3AA activation energy (Ea) was measured by kinetic experiments at 15-45 °C with and without a model PCM, wherein a significant decrease in Ea from 25.7 ± 3.2 to 13.6 ± 2.2 kcal•mol-1 was observed. We further demonstrated that oxygenated functional groups on PCM (e.g., -COOH) can accelerate HAA decarboxylation using synthesized polymers to resemble PCM. Density functional theory simulations were performed to determine the enthalpy of activation (ΔH‡) for Br3AA decarboxylation with H3O+ and formic acid (HCOOH). The presence of HCOOH significantly lowered the overall ΔH‡ value for Br3AA decarboxylation, supporting the hypothesis that -COOH catalyzes the C-C bond breaking in Br3AA. Overall, our study demonstrated the importance of a previously overlooked abiotic reaction pathway, where HAAs can be quickly converted to THMs with PCM under water treatment relevant conditions. These findings have substantial implications for DBP mitigation in water quality control, particularly for potable water reuse or pre-chlorinated water that allow direct contact between HAAs and AC during filtration as well as PAC fines traveling with finished water in water distribution systems. As such, the volatilization and relative low toxicity of volatile THMs may be considered as a detoxification process to mitigate adverse DBP effects in drinking water, thereby lowering potential health risks to consumers.

Estrogen Regulates Glucose Metabolism in Cattle Neutrophils Through Autophagy.

Hypoglycemia resulting from a negative energy balance (NEB) in periparturient cattle is the major reason for a reduced glycogen content in polymorphonuclear neutrophils (PMNs). The lack of glycogen induces PMNs dysfunction and is responsible for the high incidence of perinatal diseases. The perinatal period is accompanied by dramatic changes in sex hormones levels of which estrogen (17ß-estradiol, E2) has been shown to be closely associated with PMNs function. However, the precise regulatory mechanism of E2 on glucose metabolism in cattle PMNs has not been elucidated. Cattle PMNs were cultured in RPMI 1640 with 2.5 (LG), 5.5 (NG) and 25 (HG) mM glucose and E2 at 20 (EL), 200 (EM) and 450 (EH) pg/mL. We found that E2 maintained PMNs viability in different glucose conditions, and promoted glycogen synthesis by inhibiting PFK1, G6PDH and GSK-3ß activity in LG while enhancing PFK1 and G6PDH activity and inhibiting GSK-3ß activity in HG. E2 increased the ATP content in LG but decreased it in HG. This indicated that the E2-induced increase/decrease of ATP content may be independent of glycolysis and the pentose phosphate pathway (PPP). Further analysis showed that E2 promoted the activity of hexokinase (HK) and GLUT1, GLUT4 and SGLT1 expression in LG, while inhibiting GLUT1, GLUT4 and SGLT1 expression in HG. Finally, we found that E2 increased LC3, ATG5 and Beclin1 expression, inhibited p62 expression, promoting AMPK-dependent autophagy in LG, but with the opposite effect in HG. Moreover, E2 increased the Bcl-2/Bax ratio and decreased the apoptosis rate of PMNs in LG but had the opposite effect in HG. These results showed that E2 could promote AMPK-dependent autophagy and inhibit apoptosis in response to glucose-deficient environments. This study elucidated the detailed mechanism by which E2 promotes glycogen storage through enhancing glucose uptake and retarding glycolysis and the PPP in LG. Autophagy is essential for providing ATP to maintain the survival and immune potential of PMNs. These results provided significant evidence for further understanding the effects of E2 on PMNs immune potential during the hypoglycemia accompanying perinatal NEB in cattle.

Effect of the structure and micropore of activated and oxidized black carbon on the sorption and desorption of nonylphenol.

Activated, oxidized, and solvent-extracted black carbon samples (BCs) were produced from a shale kerogen at temperatures ranging from 250 to 500 °C by chemical activation regents (KOH, ZnCl2), oxidative regents (H2O2, NaClO), and organic solvents, respectively. Extracted organic matter (EOM) and polycyclic aromatic hydrocarbons (PAHs) were quantified in BCs, and they increased and then decreased with increasing temperature. Sorption and desorption isotherms of nonylphenol (NP) on BCs were compared with those previously reported for phenanthrene (Phen). The desorption hysteresis coefficients of NP were greater than those of Phen, while the adsorption capacities of NP were different from those of Phen. The micropore volume and micropore size were critical factors for the micropore filling mechanism of NP in BCs. The ZnCl2 activation and oxidation treatments were observed to effectively enhance the adsorption of NP and to remove native PAHs from the investigated BCs. But the KOH activation and oxidation treatments were not as efficient as expected. Moreover, the NP desorption hysteresis suggested that a hydrogen bonding and micropore deformation mechanism occurred on the extracted activated BCs. This finding improves our understanding of the sorption and desorption mechanisms of NP from the perspective of the modified BCs and their applications.

Soil labile organic carbon fractions and soil enzyme activities after 10 years of continuous fertilization and wheat residue incorporation.

Labile organic carbon (LOC) fractions and related enzyme activities in soils are considered to be early and sensitive indicators of soil quality changes. We investigated the influences of fertilization and residue incorporation on LOC fractions, enzyme activities, and the carbon pool management index (CPMI) in a 10-year field experiment. The experiment was composed of three treatments: (1) no fertilization (control), (2) chemical fertilizer application alone (F), and (3) chemical fertilizer application combined with incorporation of wheat straw residues (F + R). Generally, the F + R treatment led to the highest concentrations of the LOC fractions. Compared to the control treatment, the F + R treatment markedly enhanced potential activities of cellulase (CL), ß-glucosidase (BG), lignin peroxidase (LiP), and manganese peroxidase (MnP), but decreased laccase (LA) potential activity. Partial least squares regression analysis suggested that BG and MnP activities had a positive impact on the light-fraction organic carbon (LFOC), permanganate-oxidizable carbon (POXC), and dissolved organic carbon (DOC) fractions, whereas laccase activity had a negative correlation with those fractions. In addition, the F + R treatment significantly increased the CPMI compared to the F and control treatments. These results indicated that combining fertilization with crop residues stimulates production of LOC and could be a useful approach for maintaining sustainable production capacity in lime concretion black soils along the Huai River region of China.

Formation of Char-Like, Fused-Ring Aromatic Structures from a Nonpyrogenic Pathway during Decomposition of Wheat Straw.

Fused-ring aromatics, important skeletal components of black carbon (BC), contribute to long-term carbon (C) sequestration in nature. They have previously been thought to be primarily formed by incomplete combustion of organic materials, whereas the nonpyrogenic origins are negligible. Using advanced solid-state 13C nuclear magnetic resonance (NMR), including recoupled long-range C-H dipolar dephasing, exchange with protonated and nonprotonated spectral editing (EXPANSE), and dipolar-dephased double-quantum/single-quantum (DQ/SQ) spectroscopy, we for the first time identify fused-ring aromatics that formed during the decomposition of wheat (Triticum sp.) straw in soil under aerobic, but not anaerobic conditions. The observed formation of polyaromatic units as plant litter decomposes provides direct evidence for humification. Moreover, the estimation of the annual flux of such nonpyrogenic BC could be equivalent to 3-12% of pyrogenic BC added to soils from all other sources. Our findings significantly extend the understanding of potential sources of fused-ring aromatic C and BC in soils as well as the global C cycle.

Linking chemical structure of dissolved organic carbon and microbial community composition with submergence-induced soil organic carbon mineralization.

Much research has been devoted to investigating how water-extractable organic carbon (DOC) concentration and microbial activity regulate soil organic carbon (SOC) mineralization when soils are saturated with water. However, the relationships of DOC chemical structure and microbial community composition with SOC mineralization, as well as the relative contributions of microbial decomposers and their substrates on the mineralization rate have rarely been examined. In a laboratory experiment, we incubated two typical cropland soils (an Entisol and a Mollisol) of China for 360 days under submerged and non-submerged conditions, and we evaluated the concentration and chemical structure of soil DOC, soil microbial metabolic potential and community composition by using total C/N analysis, solution-state 1H NMR, Biolog EcoPlates, and 16S rRNA amplicon sequencing, respectively. The results showed that submergence significantly increased DOC concentration (P < 0.01) and microbial activity (P < 0.001) and changed DOC chemical structure in the Entisol (P < 0.01). In the Mollisol, it significantly increased the rate (P < 0.01) and cumulative extent (P < 0.001) of SOC mineralization and DOC concentration (P < 0.01) as well as altering the composition of the microbial community (P < 0.001). Moreover, the SOC mineralization rate was better explained by microbial community composition (Entisol: SPC = -0.71, P < 0.001; Mollisol: SPC = 0.92, P < 0.001) than by DOC concentration (Entisol: SPC = 0.21, P > 0.05; Mollisol: SPC = 0.30, P < 0.05) or DOC chemical structure (Entisol: SPC = 0.12, P > 0.05; Mollisol: SPC = -0.45, P < 0.001). Our study revealed that the bacterial community composition had a close relationship to the rate of submergence-induced SOC mineralization in both soils, but only DOC concentration and chemical structure were effective predictors of mineralization rate in the low-pH Mollisol.

Characterization of fluvo-aquic soil phosphorus affected by long-term fertilization using solution 31P NMR spectroscopy.

Reducing the applications of mineral phosphorus (P) fertilizers and supplementing them by organic fertilizers is becoming a necessary practice in the North China Plain due to overuse of mineral P fertilizers and improper disposal of organic wastes. Knowledge is needed about how the long-term substitution of mineral fertilizers by organic fertilizers affects soil P forms in order to understand soil P transformation and crop P uptake. In this study, we used solution 31P nuclear magnetic resonance (NMR) spectroscopy to characterize P forms in fluvo-aquic soil after 26 years of different fertilization management strategies, organic compost (OM), half compost in combination with half mineral fertilizer NPK (1/2 OM), mineral fertilizer NPK (NPK), mineral fertilizer NK (NK), and an unfertilized control (CK). Results showed that the P extraction efficiency using NaOH-EDTA varied from 13.0 to 27.7% for the soils of the treatments. 31P NMR spectra indicated that the majority of P was in the form of orthophosphate for all the treatments, which constituted 64.3-83.5% of the total extracted P. The application of P fertilizers significantly increased the concentrations of orthophosphate, monoesters and diesters regardless of the P fertilization method, although the proportions of monoesters and diesters were higher in CK. The proportions and concentrations of orthophosphate significantly decreased when all mineral fertilizers were replaced by compost. There was no significant difference in the proportions and concentrations of total organic P, corrected monoesters and diesters in NaOH-EDTA extracts of soils among NPK, 1/2OM and OM treatments. Decreasing mineral P fertilizers and partly replacing them by organic fertilizer in fluvo-aquic soil might increase soil test (Olsen) P and crop P uptake through the degradation of applied organic P forms.

Demonstration of Chemical Distinction among Soil Humic Fractions Using Quantitative Solid-State 13C NMR.

Humic substances (HS) are vital to soil fertility and carbon sequestration. Using multiple cross-polarization/magic-angle spinning (multiCP/MAS) NMR combined with dipolar dephasing, we quantitatively characterized humic fractions, i.e., fulvic acid (FA), humic acid (HA), and humin (HM), isolated from two representative soils (upland and paddy soils) in China under six long-term (>20 years) fertilizer treatments. Results indicate that each humic fraction showed chemical distinction between the upland and paddy soils, especially with much greater aromaticity of upland HMs than of paddy HMs. Fertilizer treatment exerted greater influence on chemical natures of upland HS than of paddy HS, although the effect was less than that of soil type. Organic manure application especially decreased the percentages of aromatic C in the upland HAs and HMs compared with the control. We concluded that humic fractions responded in chemical nature to environmental conditions, i.e., soil type/cropping system/soil aeration and fertilizer treatments.

Probing the Surface Reactivity of Pyrogenic Carbonaceous Material (PCM) through Synthesis of PCM-Like Conjugated Microporous Polymers.

Pyrogenic carbonaceous matter (PCM) is redox-active and promotes both abiotic and biotic reactions in the environment, possibly as a result of its conductivity and phenolic/quinone functional groups. However, due to the complexity of PCM, the contribution of conductivity or phenolic/quinone functional groups to its redox activity is poorly understood, which hinders its potential engineering applications. Here, we synthesized tunable conjugated microporous polymers (CMPs) that possess key properties of PCM, which can be used as PCM analogues to provide insights to PCM reactivity. Specifically, controlled incorporation of phenolic moieties into CMPs during polymer synthesis affected electron-donating capacity, while carbonization of CMPs at various temperatures altered conductivity. Both properties were then correlated with PCM reactivity measured by the decay kinetics of a model pollutant trichloronitromethane. We demonstrate that some of the prepared CMPs enabled transformation of trichloronitromethane, while no decay was observed in the absence of CMPs. Results of further investigation suggest that trichloronitromethane decay occurs by reductive dechlorination, suggesting that CMPs are electron donors and the first dissociative electron transfer from CMPs was likely to be the rate-limiting step. Conductivity but not electron-donating capacity was positively correlated with CMP-mediated trichloronitromethane decay kinetics, suggesting an important role of the electron transfer kinetics at the interface for PCM-mediated transformation of environmental pollutants.

Effects of the Chemical Structure, Surface, and Micropore Properties of Activated and Oxidized Black Carbon on the Sorption and Desorption of Phenanthrene.

The effects of the chemical structure, surface properties, and micropore of modified black carbon samples (BCs) on the sorption mechanism of hydrophobic organic contaminants (HOCs) are discussed. Activated and oxidized BCs were produced from a shale kerogen at 250-500 °C by chemical activation regents (KOH and ZnCl2) and then by oxidative regents (H2O2 and NaClO). The surface properties (water contact angel, Boehm titration, and cation exchange capacity, CEC), structural properties (advanced solid-state 13C NMR), micropore properties (CO2 adsorption), mesopore properties (N2 adsorption), and sorption and desorption properties of phenanthrene were obtained. The results showed that ZnCl2-activated BCs had higher basic surface groups, CEC values, aromatic carbon contents, micropore volumes, and adsorption volumes but exhibited lower acidic surface groups than the KOH-activated BCs did. Micropore modeling and sorption irreversibility indicated that the micropore filling was the main sorption mechanism of phenanthrene. In addition, ZnCl2 activated and NaClO oxidized BCs showed a nice regression equation between adsorption volumes and micropore volumes (CO2- V0) as follows: Q0' = 0.495 V0 + 6.28( R2 = 0.98, p < 0.001). Moreover, the contents of nonprotonated aromatic carbon, micropore volumes, and micropore sizes are the critical factors to micropore filling mechanism of phenanthrene on BCs. The size of fused aromatic rings was estimated from the recoupled 1H-13C dipolar dephasing, and the BC structural models at temperatures ranging from 300 to 500 were proposed. This finding improves our understanding of the sorption mechanism of HOCs from the perspectives of chemical structure and micropore properties.

Effects of compositions, chemical structures, and microporosity of sedimentary organic matter on degradation of benzo(a)pyrene by hydrogen peroxide.

We investigated how the degradation of 7-14C-BaP aged in sediments by H2O2 treatment was influenced by the chemical structures, compositions, and microporosity of sedimentary organic carbon (SOC). Unstable OC (USOC), stable OC (STOC), mineral-protected OC (MOC), and chemically resistant OC (ROC) fractions were fractionated. The chemical structures and microporosity of the ROC fractions were characterized by 13C solid-state nuclear magnetic resonance (NMR) and CO2 adsorption technique, respectively. A first-order, two-compartment kinetics model described the degradation process very well (R2 > 0.980). The BaP degradation ratios increased with the increasing USOC contents and decreased with the increasing ROC contents. The BaP parent compound in the aqueous solution was almost completely degraded. The considerable portions of oxidized intermediates were detected in different SOC fractions, which represented either oxidized intermediates or parent compounds. The very good multivariate regressions among the degradation kinetics parameters, SOC structures and micropore volumes demonstrated that ROC-bulk, aliphatic moieties, and microporosity played crucial roles in protecting sorbed BaP from being degraded by H2O2. The results showed that ROC, aliphatic moieties, and microporosity played vital roles in Bap degradation process in sediments during H2O2 treatment, which is reported for the first time in this study.

Labile and recalcitrant components of organic matter of a Mollisol changed with land use and plant litter management: An advanced 13C NMR study.

Soil organic matter (SOM) changes with land use and soil management, yet the controlling factors over the chemical composition of SOM are not fully understood. We applied quantitative 13C nuclear magnetic resonance and spectral editing techniques to measure chemical structures of SOM from different land use types. The land use types included a native grassland (nGL), a crop land with straw burning in the field (bCL), a restored grassland (rGL) and a cropland with straw removed out of the field (rCL) for 28years. The abundances of OCH groups from carbohydrates were higher in the SOMs of the nGL and rGL than in those of the rCL and bCL, while the abundances of OCH3 and aromatic CO groups from lignin were higher in the SOMs of the three-ever cultivated lands (rGL, rCL and bCL) than in that of the nGL. Although aromatic CC groups were most dominant in the Mollisols, they did not consistently decrease after the burnings of straw were ceased in the fields of the rCL and rGL compared to the bCL with continuous burning. In addition, the COO groups were bound with the aromatic CC groups in all the land use types, and the sizes of the aromatic clusters were affected by the land use types. The labile and recalcitrant components were correlated with SOC contents the mineral-associated and particular SOM in a contrasting way. Our results suggested that the chemical composition of SOM in the Mollisol depended on land use types, and that labile and recalcitrant components might be protected through mineral associations and aggregation, respectively. The most abundant aromatics in the Mollisols might not just be pyrogenic and could be oxidized to different extents, depending on field drainage conditions.

Biochemical stabilization of soil organic matter in straw-amended, anaerobic and aerobic soils.

Crop straw incorporation is a useful approach for increasing the quantity and changing the chemical composition of soil organic matter (SOM). This process is influenced by soil aeration. The present study investigated the stability of whole SOM, particulate organic matter (POM) and mineral-associated organic matter (MinOM) fractions with wheat straw amendment under aerobic and anaerobic conditions over a 12-month incubation period. Solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to analyze the chemical composition of whole SOM, POM and MinOM fractions. The decomposition rate of wheat straw was lower under anaerobic than under aerobic conditions (0.014 vs. 0.020day-1). Wheat straw incorporation increased the original soil organic carbon content (7.4g kg-1) under both aerobic (up to 10.2g·kg-1) and anaerobic (up to 10.3g·kg-1) conditions, but the content of mineral-associated organic carbon (MinOC) under aerobic condition (7.0g·kg-1) was significantly larger than that under anaerobic condition (4.9g·kg-1). The proportion of alkyl carbon (C) in SOM, POM and MinOM fractions was greater under anaerobic than under aerobic conditions, while the opposite was true for the proportion of O-alkyl C of SOM and POM and MinOM fractions. A/O-A indices (i.e., the ratio of alkyl C to O-alkyl C) of whole SOM, POM and MinOM were higher under anaerobic than under aerobic conditions. We conclude that wheat straw incorporation resulted in the enrichment of alkyl C in the POM and MinOM fractions under anaerobic conditions, and thus improved the stability of SOM. In this way, the decomposition of crop residue influenced SOM structural chemistry at the molecular level.