Retention of dissolved organic matter by illitic soils and clay fractions: Influence of mineral phase properties

The dependency of the retention of dissolved organic carbon (DOC) on mineral phase properties in soils remains uncertain especially at neutral pH. To specifically elucidate the role of mineral surfaces and pedogenic oxides for DOC retention at pH 7, we sorbed DOC to bulk soil (illitic surface soils of a toposequence) and corresponding clay fraction (< 2 μm) samples after the removal of organic matter and after removal of organic matter and pedogenic oxides. The DOC retention was related to the content of dithionite‐extractable iron, specific surface area (SSA, BET‐N₂ method) and cation exchange capacity (pH 7). The reversibility of DOC sorption was determined by a desorption experiment. All samples sorbed 20–40 % of the DOC added. The DOC sorption of the clay fractions explained the total sorption of the bulk soils. None of the mineral phase properties investigated was able to solely explain the DOC retention. A sorption of 9 to 24 μg DOC m^–2 indicated that DOC interacted only with a fraction of the mineral surface, since loadings above 500 μg m^–2 would be expected for a carbon monolayer. Under the experimental conditions used, the surface of the silicate clay minerals seemed to be more important for the DOC sorption than the surface of the iron oxides. The desorption experiment removed 11 to 31 % of the DOC sorbed. Most of the DOC was strongly sorbed.     

干润变性土次生碳酸盐稳定碳氧同位素特征的古环境意义

Pedogenic carbonates, found extensively in arid and semiarid regions, are important in revealing regional climatic and environmental changes as well as the carbon cycle. In addition, stable carbon and oxygen isotopic compositions of pedogenic carbonates have been used to rebuild paleoecology (biomass and vegetation) and to estimate paleotemperature and paleoprecipitation during past geological time. By utilizing the stable carbon and oxygen isotopic compositions (δ¹³C) and (δ¹⁸O) of secondary nodules in Ustic Vertisols, this study looked into the climatic and environmental changes in the dry valleys of the Yuanmou Basin, Yunnan Province, in southwestern China. The results showed that during the early Holocene, a warm-humid or hot-humid climate existed in the Yuanmou Basin, but since then fluctuations in climate have occurred, with a dry climate prevailing. A highly significant correlation (r = 0.92, n = 9) between δ¹³C and δ¹⁸O values of carbonates illustrated that there had been a continual shifting between cold-humid and warm-dry climates in southwestern China including the Yuanmou Basin since the early Holocene.     

废弃卡林型金矿区结皮苔藓植物蓄水作用和成土功能研究

通过野外调查和实验室分析,对贵州省兴义市新路废弃卡林型金矿区苔藓植物进行了研究。结果显示,该矿区共计有苔藓植物4科6属7种,未发现苔类和角苔,种类组成较单调,其中丛藓科(Pottiaceae)和真藓科(Bryaceae)为优势科;生活型有2种类型:矮丛集型(85.71%)和交织型(14.29%),矮丛集型占有绝对优势;并对该矿区结皮优势苔藓植物硬叶扭口藓、卵蒴真藓、毛口藓和小青藓的生物量、成土量、饱和吸水率和饱和吸水量进行了测定分析。结果显示,该矿区生物量为3.00～52.40g/m2;成土量为217.50～3 695.80g/m2;饱和吸水量为35.10～684.30g/m2;饱和吸水率为1 170.00%～3 637.00%。研究表明,在喀斯特石漠化严重的废弃金矿区,对于在缺少土壤,水土流失严重和植被破坏大的环境区域,苔藓植物以其特有的生态功能在石漠化治理,蓄水作用和成土功能,植被恢复及生态治理等方面起到十分重要的作用。     

运用简单线性水库模型计算Pothwar黄土平原（巴基斯坦）磷灰石损失情况

Apatite is the dominant phosphorus （P） mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents （Rajar）, Typic Calciustepts （Missa）, Udic Calciustepts （Basal）, and Udic Haplustalfs （Guliana）, were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron （oxides and oxyhydroxides） adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M（x） =M0[1 - exp（-wx）] with r^2=0.996, where M（x） is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg^-1 at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.     

Nonhydrolyzable forms of soil organic nitrogen: Extractability and composition

The chemical identity of organic nitrogen (N) containing compounds in soils is only partially known, because 20—35% of soil N can not be hydrolyzed and identified by wet‐chemical methods. Therefore a new methodology for investigations of the extractability and composition of nonhydrolyzed N was developed using a combination of selective extraction, wet‐chemical analyses and pyrolysis‐mass spectrometry. Residues of organic matter hydrolysis with 6 M HCl from particle‐size separates and whole soils of five sites in Thyrow, 2 × Halle, Lauterbach and Bad Lauchstädt (Germany) were treated with dithionite/citrate/bicarbonate (DCB) to remove pedogenic oxides and bound N‐containing compounds. Between 13 and 61% (mean 34 ± 13%) of nonhydrolyzed N (N_nhydr) was extracted with DCB. For all particle‐size separates, there was a close positive correlation between the contents of nonhydrolyzed N and DCB extractable Al and Fe, respectively. Univariate analysis of variance and Pearson correlation coefficients showed that the specific surface areas of samples were the major factor determining the contents of N_nhydr. About 30—50% of the variation in N_nhydr could be explained by the variation in the contents of pedogenic oxides. In the DCB extraction residues an additional portion of 12 to 66% of N was hydrolyzed by 6 M HCl. About 75% of total N in the DCB extracts was hydrolyzed, and 29% was identified as α‐amino‐N. Amino acid analysis showed that the DCB extracts from clay and fine silt contained all amino acids characteristic of soils. Pyrolysis‐field ionization mass spectrometry (Py‐FIMS) of a freeze‐dried DCB extract indicated the presence of peptides (about 5% of total ion intensity) and heterocyclic N‐containing compounds (about 3% of total ion intensity). In summary, these results provide evidence that organic‐mineral bonds at reactive surfaces (silicates, pedogenic oxides, alkali‐extractable organic substances) are the main factors for the nonhydrolyzability of significant amounts of organic N, including peptides. It is concluded that the processes of trapping and binding of proteinaceous compounds proceed as postulated for recent models of soil organic matter (SOM) and soil particles. Molecular mechanics calculations show large gaps between SOM and the mineral matrix and as well as fine pores and voids in SOM which have a strong potential to occlude and bind peptides (hydrogen bonds).     

次生碳酸盐结核的物质组成及元素富集特点

以黄土高原南缘武功次生碳酸盐结核为研究对象,通过分析各级结核中有机质和碳酸盐的分布特征、粒度及矿物组成,结合酸溶性元素分析,明确次生碳酸盐结核的形成过程及元素富集特点。结果表明,黄土高原南缘武功全新世古土壤发育期间形成的碳酸盐结核主要由粒径250μm结核和粒径50μm结核相互胶结而成。次生碳酸盐首先在粘粒及细粉粒表面淀积,土壤颗粒间的孔隙随着淀积的进行逐渐被次生碳酸盐填充,碳酸盐结核逐渐形成并不断生长。随着结核的生长,碳酸盐含量大幅增加,从而稀释降低了有机质含量;同时,其颗粒组成逐渐变粗,粘土矿物含量减少。各级结核中酸溶性元素均以钙(61.03~207.36g/kg)为主,且与碳酸盐含量呈正相关,因此,CaCO_3是结核中碳酸盐的主要形式。此外,酸溶性元素中含有一定量的次生无定形硅(8.90~10.70g/kg)和铝(2.78~5.06g/kg)以及粘土矿物中的钾(3.34~4.32g/kg)和镁(2.22~3.64g/kg);同时含有少量可溶性盐中的钠(0.70~0.85g/kg)。     

Characteristics of the induration of tephra-derived soils in Kyushu,Japan

The physical, chemical, and mineralogical properties as well as the micromorphology of five indurated volcanic ash soils in Kyushu, Japan were investigated. The indurated soils were divided into two types based on the physical and chemical properties. Type 1 was not indurated in its moist state, but shrank and became very hard by air-drying. Type 1 included the buried volcanic ash soils whose physical and chemical properties were similar to those of other buried volcanic ash soils except for the property of induration by air-drying. The mechanism of the induration is still unknown, although it is considered to have occurred during the long period after the deposition of tephra under the influence of soil formation processes. Type 2 included the tephra layers that were indurated in both moist and air-dried states. The carbon and clay contents of type 2 were remarkably lower than those of type 1. Type 2 had not been affected by the soil formation process but had undergone induration soon after the deposition of the tephra. Neither type 1 nor type 2 could be classified into any indurated horizons that are defined in the present soil classification system. For the improvement of soil productivity, type 1 should be harrowed thoroughly soon after its exposure to the surface, and type 2 should be harrowed or removed using farm machinery.     

类似但成土因素不同的土壤：巴西始成土的趋同演变

Soils result from the interaction of five independent formation factors.If one factor varies,while the others remain constant,different soils can be produced.Herein,we demonstrated an opposing trend,wherein two soils were similar,despite considerable differences in all factors of soil formation.We sampled two Inceptisols (Oxic Dystrudepts) formed on different parent materials (gneiss vs.mica schist),climate (tropical altimontane vs.warmer,drier plateau),topography (1 650 m,45％ slope vs.1000 m,8％ slope),time (rejuvenated vs.old,stable surface),and vegetation (rainforest vs.Cerrado savanna).The two soils had similar chemical properties,whereas the soil on mica schist had finer particle size distribution,lower porosity,and lower saturated hydraulic conductivity.These properties were related to a coarser blocky microstructure compared to the soil on gneiss.Both soils presented active mineral weathering and pronounced pedoplasmation,demonstrated by clay contents ＞ 300 g kg-1,although only the Dystrudept on gneiss possessed coarse rock fragments.The C horizons of both soils presented fragmented clay coatings suggestive of argilluviation,likely relict,because they were not observed in the B horizons.The similarities in many properties of the two Dystrudepts,despite contrasting factors of soil formation,suggest converging evolution and that soil classification at the subgroup level was efficient in grouping similar formative processes in tropical conditions.Moreover,this work revealed that similar pedogenic processes acting on different factors of soil formation can result in similar soil properties,at least for Inceptisols where further soil development is hindered by topographic limitations.     

Paleosols of the southern coastal plain of Israel

Paleosols of the S coastal plain of Israel were studied in a characteristic sequence situated in the Ruhama badlands area. At the upper part of the sequence, there is a Loessial Arid Brown Soil (Calciorthids), characteristic of the mildly arid climate of the area. The soil has two calcic horizons and four clayey layers alternating with four calcareous layers which are beneath them. Physical, chemical, and magnetic‐susceptibility data and micromorphological evidence indicate that each clayey layer together with the calcareous layer beneath it forms a single pedogenic unit. These units are similar to modern Grumusolic soils (Xeric Paleargids or Xererthic Calciargids) that occur in the semiarid belt of the S coastal plain and develop on eolian‐dust parent material. The calcareous layers are in fact calcic horizons formed by leaching of the carbonates from the clayey layers and accumulated in the form of in situ carbonate nodules. The leaching of the carbonates is not complete; they were never completely leached in the past. This feature together with a typical brown color is also characteristic of the modern soils developed in the semiarid water regime of the area. The four superimposed paleosols represent four cycles. It is suggested that they were formed in two phases. During a dry environment, a short phase of rapid eolian‐dust accumulation prevailed, followed by a stable phase of soil development in a somewhat wetter climate. Dating by optically stimulated luminescence and previous dating by ¹⁴C in the area suggest that the upper two paleosol cycles belong to the Last Glacial period whereas the other two cycles are of an earlier age. The magnetic‐susceptibility values decrease with age and react different from temperate areas. Below the four cycles, two totally leached paleosols developed on sandy parent material occur. Both paleosols have a reversed magnetic polarity and are hence older than 780 ky BP. The upper one is a Brown Mediterranean soil, and the lower one is a Red Mediterranean soil. Thin‐section evidence suggests that they formed on terrestrial sand dunes.