Sulfur and molybdenum fractionation in marine and riverine alluvium paddy soils

Intermittently submergence and drainage status of paddy fields can cause alterations in morphological and chemical characteristics of soils. We conducted a sequential fractionation study to provide an insight into solubility of Sulfur (S) and Molybdenum (Mo) in flooded alluvial paddy soils. The samples (0–15 and 15–30 cm) were taken from marine and riverine alluvial soils in Kedah and Kelantan areas, respectively, and were sequentially extracted with NaHCO₃, NaOH, HCl, and HClO₄–HNO₃. Total S in upper and lower layers of Kedah and Kelantan ranged between 273 and 1121 mg kg^?1, and 177 to 1509 mg kg^?1, respectively. In upper layers and subsoil of Kedah, average total Mo were 0.34 and 0.27 mg kg^?1, respectively. Average total Mo in Kelantan were 0.25 mg kg^?1 (surface layer) and 0.28 mg kg^?1 (subsoil). Cation exchange capacity (CEC) was positively correlated with plant available amounts of Mo in upper layers of Kedah area. Also, total and medium-term plant-available S was correlated with total carbon (C) at lower layers of Kelantan soil series. But in surface layers of Kelantan soil series, CEC was strongly correlated with total and medium-term plant-available S. Our results indicates that the influence of flooding conditions on soil S and Mo contents in paddy fields may cause long-term changes in S and Mo chemical reactivities.     

长白山北坡森林土壤汞的含量和形态分布

分别于2009年4月和9月对长白山北坡的土壤样品进行了采集,研究北方森林地区不同海拔土壤样品中的总汞和甲基汞的分布情况.长白山土壤THg和MeHg含量分别为0.08～0.73 mg·kg-1和0.05～0.56 μg·kg-1,库存量分别为97 kg·km-2和128 g·km-2,高于吉林省背景值,MeHg的最高含量...     

Formation of soil organic carbon pool is regulated by the structure of dissolved organic matter and microbial carbon pump efficacy: A decadal study comparing different carbon management strategies

To achieve long-term increases in soil organic carbon (SOC) storage, it is essential to understand the effects of carbon management strategies on SOC formation pathways, particularly through changes in microbial necromass carbon (MNC) and dissolved organic carbon (DOC). Using a 14-year field study, we demonstrate that both biochar and maize straw lifted the SOC ceiling, but through different pathways. Biochar, while raising SOC and DOC content, decreased substrate degradability by increasing carbon aromaticity. This resulted in suppressed microbial abundance and enzyme activity, which lowered soil respiration, weakened in vivo turnover and ex vivo modification for MNC production (i.e., low microbial carbon pump “efficacy”), and led to lower efficiency in decomposing MNC, ultimately resulting in the net accumulation of SOC and MNC. In contrast, straw incorporation increased the content and decreased the aromaticity of SOC and DOC. The enhanced SOC degradability and soil nutrient content, such as total nitrogen and total phosphorous, stimulated the microbial population and activity, thereby boosting soil respiration and enhancing microbial carbon pump “efficacy” for MNC production. The total C added to biochar and straw plots were estimated as 27.3–54.5 and 41.4 Mg C ha⁻¹, respectively. Our results demonstrated that biochar was more efficient in lifting the SOC stock via exogenous stable carbon input and MNC stabilization, although the latter showed low “efficacy”. Meanwhile, straw incorporation significantly promoted net MNC accumulation but also stimulated SOC mineralization, resulting in a smaller increase in SOC content (by 50%) compared to biochar (by 53%–102%). The results address the decadal-scale effects of biochar and straw application on the formation of the stable organic carbon pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content.     

黄土丘陵区植被与地形特征对土壤和土壤微生物生物量生态化学计量特征的影响

研究黄土丘陵区植被与地形特征对土壤和土壤微生物生物量生态化学计量特征影响有助于深入理解黄土丘陵区不同植被带下土壤和土壤微生物相互作用及养分循环规律.选择黄土丘陵区延河流域3个植被区(森林区、森林草原区、草原区)和5种地形部位(阴/阳沟坡、阴/阳梁峁坡、峁顶)的土壤作为研究对象,利用生态化学计量学理论研究植被和地形对土壤和土壤微生物生物量生态化学计量特征的影响.结果表明: 土壤及土壤微生物生物量碳、氮、磷含量在不同地形之间的差别主要表现在沟坡位置和阴坡高于其他坡位和阳坡.植被类型的变化对两个土层(0～10、10～20 cm)土壤和土壤微生物生物量碳、氮、磷的影响均达到显著水平,坡向对表层(0～10 cm)土壤和土壤微生物生物量碳、氮、磷的影响强于坡位,而在10～20 cm土层,坡位对土壤和土壤微生物生物量碳、氮、磷影响更显著.植被类型显著影响土壤C∶N、C∶P、N∶P和土壤微生物生物量C∶N、C∶P,坡向和坡位仅影响土壤C∶P和N∶P,植被类型的变化是影响土壤C∶N的主要因素.同时,植被类型对土壤养分和微生物生物量碳、氮、磷含量及其生态化学计量特征的影响大于地形因子.标准化主轴分析结果表明,黄土丘陵区不同植被带土壤微生物具有内稳性,特别在草原带,土壤微生物生物量生态化学计量学特征具有更加严格的约束比例.在黄土丘陵区,土壤微生物生物量N∶P或许可以作为判断养分限制的另一个有力工具,若将土壤微生物生物量N∶P与植物叶片N∶P配合使用可能有助于我们更加精确地判断黄土丘陵区的土壤养分限制情况.     

Comparative characterization of the conjugation capacity and large plasmids in native strains of Bacillus subtilis from different regions of the East European Plain

The properties of large plasmids harbored by Bacillus subtilis strains isolated from soils of Moscow and Moscow oblast and from different regions of the Republic of Belarus have been studied. All large plasmids in the collection of strains from Belarus were capable of conjugative mobilization of the small plasmid pUB110 and were similar in size and other properties. Most of the tested plasmids harbored by strains isolated from Moscow soils had no mobilization ability; they were of different sizes and showed no homology with the replication region of plasmids from the Belarussian collection. The uniformity of the plasmids present in strains from Belarussian soils may be due to their active horizontal transfer under natural conditions.     

Cs phytoremediation by Sorghum bicolor cultivated in soil and in hydroponic system

Cs accumulation characteristics by Sorghum bicolor were investigated in hydroponic system (Cs level at 50–1000 μmol/L) and in soil (Cs-spiked concentration was 100 and 400 mg/kg soil). Two varieties of S. bicolor Cowly and Nengsi 2# grown on pot soil during the entire growth period (100 days) did not show significant differences on the height, dry weight (DW), and Cs accumulation. S. bicolor showed the potential phytoextraction ability for Cs-contaminated soil with the bioaccumulation factor (BCF) and the translocation factor (TF) values usually higher than 1 in soil system and in hydroponic system. The aerial parts of S. bicolor contributed to 86–92% of the total removed amounts of Cs from soil. Cs level in solution at 100 μmol/L gave the highest BCF and TF values of S. bicolor. Cs at low level tended to transfer to the aerial parts, whereas Cs at high level decreased the transfer ratio from root to shoot. In soil, the plant grew well when Cs spiked level was 100 mg/kg soil, but was inhibited by Cs at 400 mg/kg soil with Cs content in sorghum reaching 1147 mg/kg (roots), 2473 mg/kg (stems), and 2939 mg/kg (leaves). In hydroponic system, average Cs level in sorghum reached 5270 mg/kg (roots) and 4513 mg/kg (aerial parts), without significant damages to its biomass at 30 days after starting Cs treatment. Cs accumulation in sorghum tissues was positively correlated with the metal concentration in medium.     

生物炭对土壤氮循环的影响研究进展

在定性资料调研的基础上,基于ISI Web of Science数据库,采用文献计量学方法,针对"生物炭对土壤氮循环的影响"及其分支技术进行文献检索、数据整理、分类以及主题分析,从国际整体研究态势和分支技术主题两个角度探讨了目前国内外生物炭影响土壤氮循环方面的研究进展,并从生物炭对土壤N_2O排放、肥料利用率、硝化速率、NH_4~+/NH_3吸附、NO_3~-吸附以及土壤微生物氮素固持等6个方面的影响进行了详细论述。近年来,生物炭对土壤氮循环的影响研究急剧增温,发文量逐年增加,截止2014年6月,SCI数据库中共检索到2468篇论文。其中,期刊论文2188篇、综述性论文93篇,其它类论文177篇。美国、加拿大、英国等欧美国家在该领域的研究中占有明显优势,而自2010年以来,中国已成为该领域全球第一的年发文大国。发文热点主要集中在生物炭对土壤N_2O排放和对氮肥利用率的影响2个方面,占总发文量的73.7%。从6个方面的分支技术主题来看,生物炭的影响作用争议性较大。大部分研究认为,生物炭能够抑制土壤N_2O排放、提高氮肥利用率、促进土壤硝化速率、提高土壤对NH_4~+/NH_3和NO_3~-的固持作用以及土壤微生物氮素固持作用等,但也有研究表明生物炭会促进土壤N_2O排放、抑制土壤硝化速率,且不具备NO_3~-固持能力。这主要与生物炭的类型、老化过程,以及土壤类型及其含水孔隙率等密切相关。总之,探讨了生物炭对土壤氮循环影响的研究动态、热点及主要结论,为深入了解生物炭对土壤理化特性影响的作用机制提供了一定研究思路,为生物炭的农业应用提供了一定借鉴和参考。     

Rapid degradation of pyrogenic carbon

Pyrogenic carbon (PC‐ charcoal, biochar or black carbon) represents a poorly understood component of the global carbon (C) cycle, but one that has considerable potential to mitigate climate change through provision of long‐term soil C sequestration. Mass balance calculations suggest global PC production and stocks are not in balance, indicating a major gap in our understanding of the processes by which PC is re‐mineralized. We collected PC samples derived from the same wood material and exposed to natural environmental conditions for 1 and 11 years. We subjected these materials to repeated laboratory incubation studies at temperatures of up to 60 °C, as ground surface temperatures above 30 °C and up to 60 °C occur regularly over a significant area of the tropics and sub‐tropics. Mineralization rates were not different for the two samples and followed an exponential Arrhenius function that suggest an average turnover time of 67 years for conditions typical of a tropical savannah environment. Microbial biomass as measured by chloroform fumigation and DNA extractions was the same for the two samples, but abiotic CO₂ production was lower for the fresh PC sample than that for the aged sample. Nuclear magnetic resonance spectroscopy, hydrogen pyrolysis and scanning electron microscopy demonstrate that the measured CO₂ production originates dominantly from polycyclic aromatic compounds rather than any minor labile components. Therefore, rapid, sub‐centennial rates of re‐mineralization of PC on the soil surface in tropical and sub‐tropical environments may represent a major and hitherto unidentified mechanism for balancing the PC production at the global scale.     

Impacts of ISCO Persulfate,Peroxide and Permanganate Oxidants on Soils: Soil Oxidant Demand and Soil Properties

The consumption of in-situ chemical oxidation (ISCO) oxidant by soil oxidizable matter (OM), termed the soil oxidant demand (SOD), is an essential factor when designing treatments for successful remediation at an ISCO site. This study aims to assess the impact of different oxidants on SOD and the soil itself, using the Taguchi experimental design. Five oxidation systems, including persulfate (PS), hydrogen peroxide (HP), permanganate (PM), Fe²⁺ activated PS and Fe²⁺ activated HP, and four factors including oxidant concentration, activator concentration, reaction time, and pH were investigated. The results of the Taguchi analysis in this study show that oxidant concentration had the greatest effect on the SOD. Other factors also affected the SOD and the optimum conditions for achieving a lower SOD were determined using the Taguchi design method. Additionally, original and oxidized soils were analyzed using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer to determine the surface morphology and chemical composition of the samples. Variations in soil organic carbon levels and total soil bacterial counts were recorded and the speciation of soil minerals (Fe, Mn, Cu, and Zn) was analyzed.