Spectral fingerprinting of soil organic matter composition

Large scale environmental monitoring schemes would benefit from accurate information on the composition of soil organic matter (SOM), but so far routine procedures for describing SOM composition remain a chimera. Here, we present the initial assessment of a two step strategy for expeditious determination of SOM composition that involves: (i) building infrared fingerprints from near and mid infrared spectroscopies, two rapid and cheap yet reliable technologies; and (ii) calibrating such infrared fingerprints with multivariate chemometrics from a molecular mixing model based on the more expensive and time consuming ¹³C nuclear magnetic resonance technique, which discriminates five biochemical components: carbohydrate, protein, lignin, lipid and black carbon. We show fair to excellent predictive ability of the calibrated infrared fingerprints for four out of these five biochemical components, with cross-validated ratios of performance to inter-quartile distance from 3.2 to 8.3, on a small set of 23 soil samples with a wide range of organic carbon content (12–500 g/kg). Multivariate calibration models were highly selective (<2% of infrared data were used for all models). However, the specificity to one particular biochemical component of the infrared wavebands automatically selected by each model was relatively low, except for lipid. Achieving direct predictions of SOM composition on unknown soil samples with infrared spectroscopy alone will require further independent validation and a larger number of samples. Overall, the implementation of our strategy at a broader scale, based on available ¹³C nuclear magnetic resonance soil libraries, could provide a cost effective solution for the routine assessment of SOM composition.     

Pyrolysis-combustion C dating of soil organic matter

Radiocarbon (¹⁴C) dating of total soil organic matter (SOM) often yields results inconsistent with the stratigraphic sequence. The onerous chemical extractions for SOM fractions do not always produce satisfactory ¹⁴C dates. In an effort to develop an alternative method, the pyrolysis-combustion technique was investigated to partition SOM into pyrolysis volatile (Py-V) and pyrolysis residue (Py-R) fractions. The Py-V fractions obtained from a thick glacigenic loess succession in Illinois yielded ¹⁴C dates much younger but more reasonable than the counterpart Py-R fractions for the soil residence time. Carbon isotopic composition (δ¹³C) was heavier in the Py-V fractions, suggesting a greater abundance of carbohydrate- and protein-related constituents, and δ¹³C was lighter in the Py-R fractions, suggesting more lignin- and lipid-related constituents. The combination of ¹⁴C dates and δ¹³C values indicates that the Py-V fractions are less biodegradation resistant and the Py-R fractions are more biodegradation resistant. The pyrolysis-combustion method provides a less cumbersome approach for ¹⁴C dating of SOM fractions. With further study, this method may become a useful tool for analyzing unlithified terrestrial sediments when macrofossils are absent.     

Contribution of lipids to the nonlinear sorption of polycyclic aromatic hydrocarbons to soil organic matter

The sorption isotherms of benzene, naphthalene, fluorene and phenanthrene for a suite of whole and lipid-extracted soils are presented. The sorption of benzene to two different peats displays linear characteristics which are consistent with the partitioning model of sorption. The sorption of the PAHs to three different mineral soils show marked nonlinear character. The nonlinear sorptive character of the soil organic matter can be described by site specific sorption occurring within the soil organic matrix. Removal of the lipids via Soxhlet extraction increases the nonlinear character of the sorption isotherms as well as doubles the sorptive capacity of the mineral soils for the PAHs studied. This indicates that the lipids naturally present in the soil strongly compete for hydrophobic sorption sites present in the soil organic matter matrix.     

不同土壤有机质组分对憎水有机物的吸附机理研究

采用完全混合一步平衡反应实验方法，选择菲、萘、三氯苯和二甲苯作为憎水有机物(HOCs)的探针，研究了它们在土壤及其中的胡敏酸、胡敏素等有机质组分中的等温平衡吸附行为，探讨了非线性吸附的机制。结果表明，HOCs在水与土壤体系中表现为非线性吸附，其非线性的吸附行为主要受到土壤有机质(SOMs)的控制。SOMs具有高度不均匀的性质，HOCs表现出非线性吸附行为是其在不同的SOMs相扩散转移以及在相对聚结的胡敏素和“黑炭”的表面吸附的结果。     

Fate of microbial biomass-derived amino acids in soil and their contribution to soil organic matter

Soil organic matter (SOM) is important for soil fertility and for the global C cycle. Previous studies have shown that during SOM formation no new compound classes are formed and that it consists basically of plant- and microorganism-derived materials. However, little data on the contribution from microbial sources are available. Therefore, we investigated previously in a model study the fate of C from ¹³C-labelled Gram-negative bacteria in soil (Kindler, R., Miltner, A. Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil – mineralization and contribution to SOM. Soil Biology and Biochemistry 38, 2860–2870) and showed that 44% of the bulk ¹³C remained in the soil. Here we present the corresponding data on the fate of amino acids hydrolysed from proteins, which are the most abundant components of microbial biomass. After 224 days incubation, the label in the total amino acids in the soil amended with ¹³C-labelled cells decreased only to >95%. The total amino acids therefore clearly showed a lower turnover than the bulk ¹³C and a surprisingly stable concentration. Proteins therefore have to be considered as being stabilised in soil in dead, non-extractable biomass or cell fragments by known general stabilisation mechanisms. The label in the amino acids in a fraction highly enriched in living microbial biomass decreased to a greater extent, i.e. to 25% of the initially added amount. The amino acids removed from this fraction were redistributed via the microbial food web to non-living SOM. All amino acids in the microbial biomass were degraded at similar rates without a change in isotopic signature. The nuclear magnetic resonance (NMR) spectra of the soils were very similar and indicate that the residues of the degraded microbial biomass were very similar to those of the SOM and are a significant source for the formation of the SOM.     

Fate of bacterial biomass derived fatty acids in soil and their contribution to soil organic matter

Soil organic matter (SOM) is a major pool of the global C cycle and determines soil fertility. The stability of SOM strongly depends on the molecular precursors and structures. Plant residues have been regarded as the dominant precursors, but recent results showed a major contribution of microbial biomass. The fate of microbial biomass constituents has not yet been explored; therefore, we investigated the fate of fatty acids (FA) from ¹³C labeled Gram-negative bacteria (Escherichia coli) in a model soil study [Kindler, R., Miltner, A., Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil—mineralization and contribution to SOM. Soil Biology & Biochemistry 38, 2860–2870]. After 224 days of incubation, the label in the total fatty acids (t-FA) in the soil decreased to 24% and in the phospholipid fatty acids (PLFA) of living microbes to 11% of the initially added amount. Since the bulk C decreased only to 44% in this period, the turnover of FA is clearly higher indicating that other compounds must have a lower turnover. The ¹³C label in the t-FA reached a stable level after 50 days but the label of the PLFA of the living microbial biomass declined until the end of the experiment. The isotopic enrichment of individual PLFA shows that the biomass derived C was spread across the microbial food web. Modelling of the C fluxes in this experiment indicated that microbial biomass is continuously mineralized after cell death and recycled by other organisms down to the 10% level, whereas the majority of biomass derived residual bulk C (～33%) was stabilized in the non-living SOM pool.     

Sedimentary matter and organic compounds in the aerosols and surface waters along the Transatlantic section

Concentrations and composition of suspended particulate matter and organic compounds (OC), including Сorg, lipids, hydrocarbons (HC), and pigments, were determined in the near-water aerosol layer and in surface waters on the meridional section across the Atlantic Ocean from the port of Ushuaia to the port of Gdansk (Cruise 47^th of the R/V Akademic Ioffe, March 26–May, 7, 2015). It was established that the distribution of OC (except for pigments) in aerosols, in general, repeats the distribution of particle number and weight concentrations of aerosols, with maximums in the influence zone of fluxes from Patagonia and African deserts. The concentrations of aerosols changed within wide ranges: from 1237 to 111739 particles/L for 0.3–1 μm fraction; and from 0.02 to 19.890 μg/m³ for aerosols collected by network method (flux of 0.02–34.4 mg/m² day). The contrasting mineral composition of aeolian material reflects the diversity of its provenances. In surface waters, the studied compounds were accumulated in the frontal river–sea area (runoff of the Rio-Colorado River) and with approaching the coast, especially in the English Channel. A simultaneous change of concentrations of suspended particulate matter and OC is observed only in open oceanic waters.     

有机质含量对软土力学性质影响效应分析

通过对软土中有机质含量及物理力学指标的分析和研究,阐明了软土中有机质含量与物理力学参数之间的关系,从力学角度探讨了有机质含量对软土力学效应的影响。研究结果表明:随着有机质含量的增加,软土中的含水量,孔隙比等呈线性增加,而软土的原状土与重塑土的十字板剪切强度、静力触探比贯入阻力、渗透系数、固结系数都是减小的。当有机质含量为1.74%时,软土的物理力学性质发生变化,力学软化效应尤为显著,且此时软土的渗透能力达到最大。     

岩溶区土壤有机质空间变异性分析

采用GIS和地统计学研究土壤有机质（SOM）的空间分布、影响因素和预测是指导农业生产、环境治理和土壤碳储计量的重要手段。基于广西马山县北部岩溶区表层土壤 (0~20 cm)的441个SOM数据,建立普通克里格(OK)、回归克里格（RK）,以及结合辅助变量的地理加权回归克里格(GWRK)、残差均值（MM_OK）和中值（MC_OK）均一化克里格的5种模型,并比较其预测精度,旨在探讨岩溶区SOM制图中地统计学方法的适用性。结果表明：（1）SOM的变异系数为37.30%,属于中等空间变异;（2）岩溶区SOM空间变异受土地利用方式、土壤类型和地形因子等因素共同影响,SOM高值区分布在西北部、西部和东部等石灰土分布的岩溶区和水田,低值区位于北部红水河沿岸的冲积土地带;（3）RK、GWRK、MM_OK和 MC_OK对SOM解释能力均较优,可用于岩溶区SOM预测制图。结合辅助变量因子的GWRK预测模型能有效消除空间变异因素的影响,克服岩溶区SOM含量的空间非平稳性,从而提高SOM含量模型的稳定性和精度,同时MC_OK模型能提高预测的准确度。     

有机质对海相软土物理力学特性的影响效应分析

有机质是海相软土的重要组成部分,其对土体物理力学性质的影响有待深入研究。以连云港地区全新世海相软土为例,进行百组土体有机质物理力学试验。结果表明,研究区软土有机质含量平均值为0.98%,在0.90%~1.00%这个区间分布最为广泛。有机质含量在空间上分布不均,平行海岸线较垂直海岸线土体有机质含量变化小,自上向下变化规律复杂,但随着深度的增加有机质含量有增加的趋势;有机质含量与土体天然含水率、塑限、液限在0.01水平上显著正相关,与土体天然密度、干密度和比重在0.01水平上显著负相关,与土体粉粒含量在0.05水平上显著正相关,与土体黏粒含量相关性差;有机质含量与固结压力≤400 kPa阶段的孔隙比在0.01水平上显著正相关,与固结压力>400 kPa时的孔隙比相关性变差,这与有机质形成的复合体被破坏有关;海相软土黏土矿物、含盐量及含水率高,有机质与黏土矿物在碱性环境多通过阳离子键桥的方式来结合,形成有机复合体,可能参与千年及万年尺度的碳循环;研究土层最大埋深达30 m,符合有机质深埋的演化规律,而研究土体沉积时间距今最高才约8000 a,推测研究土体有机质还未达到平衡状态,还在进一步的循环演化过程当中。上述相关研究成果对海相软土分布区工程建设具有一定的参考价值。     

Litter production and mineral element input to the forest floor in a Central Amazonian forest

The study investigates the seasonal and element patterns of litterfall at two particular sites of terra firme forest in the central Amazon. The input of elements such as C, N, P, S, K, Ca, Mg, na, Zn, Fe, Al, Mn, B and Cu was thoroughly evaluated in terms of site variability, mass flow of organic compounds of various litter compartments and elemental return flow. The results were compared with recent studies on literfall in the humid tropics.Bolsista do CNPq — Conselho Nacional de Desenvolvimento Cientifico e Tecnológico.     

Chemical characterization of microbial-dominated soil organic matter in the Garwood Valley, Antarctica

Despite its harsh environmental conditions, terrestrial Antarctica contains a relatively large microbial biomass. Natural abundance carbon and nitrogen stable isotope signatures of organic materials in the dry valleys indicate mixed provenance of the soil organic matter (SOM) with varying proportions of contributions from lichens, mosses, lake-derived algae and cyanobacteria. Here we employed two complementary analytical techniques, biomarker measurements by gas chromatography/mass spectrometry and solution-state ¹H nuclear magnetic resonance spectroscopy, to provide further information at a molecular-level about the composition and possible source of SOM in the Garwood Valley, Antarctica. The predominance of branched alkanes and short-chain lipids in the solvent extracts indicates that the primary contribution to the SOM was microbial-derived. Chemical structures in the NaOH extracts from soils were also dominated by amide, peptides, and a CH₃-dominating aliphatic region that were characteristic of microbial signatures. Furthermore, the SOM in the Garwood Valley contained compounds that were different from those in the cyanobacteria-dominated mat from a nearby lake (including monoethyl alkanes and enriched side-chain protons). This observation suggests that easily degradable carbon sources from the nearby lake did not dominate the SOM, which is consistent with a fast turnover of the mat-derived organic matter found in the valley. This study highlights the important role of native soil microbes in the carbon transformation and biogeochemistry in terrestrial Antarctica.     

Molecular level analysis of long term vegetative shifts and relationships to soil organic matter composition

Soil organic matter (SOM) is one of the earth’s largest reservoirs of actively cycled carbon and plays a critical role in various ecosystem functions. In this study, mineral soils with the same parent material and of similar approximate age were sampled from the same climatic region in Halsey, Nebraska to determine the relationship between overlying vegetation inputs to SOM composition using complementary molecular level methods (biomarker analyses and solid state ¹³C nuclear magnetic resonance (NMR) spectroscopy). Soil samples were collected from a native prairie and cedar and pine sites planted on the native prairie. Free and bound lipids isolated from the pine soil were more enriched in aliphatic and cutin-derived compounds than the other two soils. Cinnamyl type lignin-derived phenols were more abundant in the grassland soil than in the pine and cedar soils. Acid to aldehyde ratios (Ad/Al) for vanillyl and syringyl type phenols were higher for the pine soil indicating a more advanced stage of lignin oxidation (also observed by ¹³C NMR) in the soil that has also been reported to have accelerated carbon loss. In agreement with the more abundant aliphatic lipids and cutin-derived compounds, solid state ¹³C NMR results also indicated that the SOM of the pine soil may have received more aliphatic carbon inputs or may have lost other components during enhanced decomposition. The observed relationship between vegetation and SOM composition may have important implications for global carbon cycling as some structures (e.g. aliphatics) are hypothesized to be more recalcitrant compared to others and their accumulation in soils may enhance below ground carbon storage.     

Sedimentary environments of organic matter from Middle Permian source rocks in northern Xinjiang, China

1IntroductionThe formation of the Junggar,Turpan and Ili ba-sins is ascribed to Hercynian orogeny between theJunggar and Tianshan Mountains during the MiddlePermian.The rock assemblage of thick and stable sedi-mentary dark muddy shales interbedded with th…     

Sedimentary organic matter in condensed sections from distal oxic environments: examples from the Mesozoic of SE France

A detailed analysis of sedimentary organic matter (or palynofacies) was carried out on thermally immature to early mature Upper Jurassic and Hauterivian condensed intervals in deep-sea carbonate–marl alternations outcropping in the Vocontian Basin (SE France). All the condensed sections studied are characterized by intense bioturbation and very low organic carbon content (< 0·25 wt.%), indicative of oxic depositional conditions. Oxic condensed sections display variable palynofacies signatures, which are best illustrated by: (1) the ratio of continental to marine constituents; (2) the ratio of opaque to translucent phytoclasts (i.e. woody debris) and (3) the preservation of palynomorphs (based on fluorescence intensity and morphological preservation state in transmitted light microscopy). Both of the ratios increase with the degree of palynomorph degradation, which shows that phytoclasts, especially the opaque ones, become relatively concentrated in the most degraded facies. These observations lead to the classification of oxic condensed sections into three organic facies types showing different degrees of preservation and palynofacies signatures. Type 1 organic facies display intense degradation and are characterized by high values of the ratio of continental to marine fraction. They record unfavourable depositional environments for preservation of organic matter. Type 2 organic facies are most common and are characterized by a decreasing value of the ratio of continental to marine fraction. Type 3 organic facies display the same trend of the ratio of continental to marine fraction as type 2, but the palynomorph assemblage is better preserved. Type 1 and type 3 organic facies are relatively rare. Recognizing these organic facies types is important when analysing the relationship between sedimentary organic matter and sequence stratigraphy, because it allows the use of the appropriate palynofacies parameters. In particular, the use of the ratio of continental to marine constituents, usually a very good indicator of regressive–transgressive trends, becomes questionable in highly degraded intervals. Moreover, distinguishing between well-preserved or highly degraded palynofacies in condensed intervals provides valuable information on the oxicity of the depositional environment.     

有机质固化土的强度及微观结构试验研究

通过无侧限抗压强度试验对比分析了有机质含量、水泥和石膏掺量对水泥固化土和XGL2005固化土强度形成规律的影响。分析结果表明,XGL2005固化土的强度均不同程度地高于水泥固化土的强度,而且强度增长也快于水泥固化土。结合抗压强度试验和扫描电镜试验分析了固化土微观结构变化和强度发展之间的对应关系。     

Organic pollutants associated with macromolecular soil organic matter: Mode of binding

A study of ether-linked moieties in macromolecular bound residues of polycyclic aromatic hydrocarbons (PAH) generated in bioremediation experiments was performed using high temperature hydrolysis degradation with subsequent analysis of the products by GC-MS. This hydrolysis reaction was specifically designed to cleave ether bonds including relatively stable diarylether structures. Among the reaction products, aromatic alcohols representing typical microbiologically derived metabolites of PAH were found in addition to natural compounds. Thus, parts of the bound residues appeared to be linked within the macromolecular material by ether bonds. Model experiments with an oxidoreductase enzyme and aromatic alcohols indicate the formation of these ether bonds to be an enzyme-catalysed process.     

Soil organic carbon within the vadose zone of a floodplain

Past studies have focused on carbon variation in the upper 1 m of the soil profile. However, there is limited information on carbon variation at deeper depths (e.g., 0–4 m) and mathematical functions to extrapolate carbon content at these depths. The objective of this study was therefore to assess the vertical variation in SOC (reached 4 m) of the Tarim River floodplain in northwestern China. The vertical distribution in SOC was described by exponential and power functions based on (1) soil depth, (2) soil depth and silt content, (3) soil depth and SOC at the shallowest and deepest depths, (4) soil depth, silt content, and SOC at the shallowest and deepest depths, and (5) soil depth and SOC at the shallowest depth. We found SOC content decreased with depth from 6.82 g kg^?1 at 0–0.2 m to?<?1.0 g kg^?1 below 3.2–3.4 m averaged across five locations along the floodplain. Both the power and exponential functions provided a good fit to the measured data in the upper 1 m of the soil profile, whereas the power function provided a better fit to the data when extrapolating to a depth of 3–4 m. The power function describing SOC as a function of soil depth, silt content, and SOC at the shallowest and deepest depths best portrayed the distribution in SOC with depth. Considering the cost and labor in measuring soil properties, our results suggest that SOC at the shallowest depth can provide good estimates of the vertical distribution in SOC in a floodplain.