微生物絮凝剂絮凝机理的研究概况及例证

微生物絮凝剂是一类由微生物产生并分泌到细胞外具有絮凝活性的代谢产物。微生物絮凝剂的絮凝机理比传统絮凝理论更复杂,国内外学者对此进行了大量研究。总结近年来国内外研究的相关文献,归纳了关于微生物絮凝剂絮凝理论的各种学说及其例证,指出了现在研究中存在的问题,并对今后的研究方向进行了展望。     

活性黑对黄孢原毛平革菌锰过氧化物酶的影响

观察了活性黑KN-B(Reactive Rlack KN-B,RB KN-B)对黄孢原毛平革菌(Phanerochaete chrysosporium)锰过氧化物酶(MnP)酶活力和菌丝超微结构的影响以及黄孢原毛平革菌对RB KN-B的降解.于P.chrysosporium培养液MnP酶活达最高前,分别加入质量浓度为50 mg/L,200 mg/L,350 mg/L和500 mg/L的RB KN-B.分光光度法检测培养液MnP酶活,电镜观察菌丝超微结构的影响,紫外-可见光谱法检测培养液中RB KN-B的降解.结果显示,1)与对照组相比,50 mg/L RBKN-B组的MnP酶活力增强,200 mg/L、350 mg/L和500 mg/L组的MnP酶活力均显著低于对照组;2)电镜观察显示,经RB KN-B作用后,菌丝细胞膜受损,细胞内含物减少,胞质浓缩,出现质壁分离现象,500mg/L组有大量细胞解体;3)紫外-可见光谱扫描显示,RB KN-B经黄孢原毛平革菌降解,可见光波段最大吸收峰由598 nm移至525 nm和556 nm,峰值减小,紫外波段的吸收峰由315 nm移至352 nm.结果显示,黄孢原毛平革菌对RB KN-B的反应类似机体对不良环境因子的应激反应,经历了诱导、抑制及衰退的过程;RB KN-B对黄孢原毛平革菌菌丝细胞超微结构的损伤随RB KN-B浓度增高而增强,表明RBKN-B对MnP酶活的抑制与黄孢原毛平革菌结构受损密切相关;黄孢原毛平革菌对RB KN-B具有一定的降解能力,其中MnP作为关键酶起了重要的作用.     

Soils and geomedicine

Geomedicine is the science dealing with the influence of natural factors on the geographical distribution of problems in human and veterinary medicine. Discussions on potential harmful impacts on human and animal health related to soil chemistry are frequently focused on soil pollution. However, problems related to natural excess or deficiency of chemical substances may be even more important in a global perspective. Particularly problems related to trace element deficiencies in soils have been frequently reported in agricultural crops as well as in livestock. Deficiencies in plants are often observed for boron, copper, manganese, molybdenum, and zinc. In animals deficiency problems related to cobalt, copper, iodine, manganese, and selenium are well known. Toxicity problems in animals exposed to excess intake have also been reported, e.g., for copper, fluorine, and selenium. Humans are similar to mammals in their relations to trace elements and thus likely to develop corresponding problems as observed in domestic animals if their supply of food is local and dependent on soils providing trace element imbalances in food crops. In large parts of Africa, Asia, and Latin America, people depend on locally grown food, and geomedical problems are common in these parts of the world. Well-known examples are Keshan disease in China associated with selenium deficiency, large-scale arsenic poisoning in Bangladesh and adjacent parts of India, and iodine deficiency disorders in many countries. Not all essential elements are derived only from the soil minerals. Some trace elements such as boron, iodine, and selenium are supplied in significant amounts to soils by atmospheric transport from the marine environment, and deficiency problems associated with these elements are therefore generally less common in coastal areas than farther inland. For example, iodine deficiency disorders in humans are most common in areas situated far from the ocean. There is still a great need for further research on geomedical problems.     

Size fractionation and characterization of nanocolloidal particles in soils

A protocol was developed to fractionate soil particles down to the nanocolloid scale by combining sieving, sedimentation, centrifugation, and cross-flow filtration (CFF). The validity of the method and the performance of the CFF system were tested by characterizing fractions using laser granulometry, electron microscopy, and chemical analysis. The 0.1-μm-pore-size membrane CFF system effectively retained nanocolloids (<0.1 μm) as shown by laser granulometry and observed directly by transmission electron microscopy. However, environmental scanning electron microscopy images of freeze-dried colloids were very different from their TEM counterparts, suggesting that sample preparation influenced microscopy imaging. Chemical analysis of Cu, Cd, and organic carbon in each fraction showed that the concentrations of these components increased as particle size decreased, indicating colloids and nanocolloids play an important role in retaining trace metals. Particle-size fractionation combined with chemical analysis and electron microscopy can provide insight into the nature and properties of nanocolloids in soil.     

Modelling of spatio-temporal population dynamics of earthworms under wetland conditions—An integrated approach

Both the effects of earthworms on soils and the effects of soil conditions on earthworms have been studied with the help of experiments and modelling. This paper provides a model architecture allowing coupling both effects to a dynamic interaction in changing environmental conditions. We chose for a spatio-temporally explicit model and focussed on wetland conditions. Soil temperature and humidity have been modelled by means of finite volumes and were used to determine the spatial habitat suitability. The life cycles of earthworms have been modelled by Leslie matrices where soil humidity, soil temperature and population densities have been used to parametrize survival and transition probabilities. Earthworm dispersion has been described by a cellular automaton of the domain providing spatial population densities for both the life cycle submodel and the soil conditions submodel.     

气候变化对亚高山暗针叶林土壤温室气体排放的影响

利用生物地球化学模犁Forest-DNDC模拟气候变化对贡嘎山亚高山暗针叶林土壤温室气体的释放的影响.以位于贡嘎山东坡海拔3 000 m的峨眉冷杉(Abies fabri)中龄林为研究对象,以1999-2006年8年的日气候数据进行平均得到的日平均最高温度、日平均最低温度和日平均降水总最作为基线(Base)气候情景,另外设置了温度+2℃(升)、温度.2℃(T-)、降水量+20%(P+)、降水量-20%(P-)、温度十2℃同时降水量+20%(T+P+)、温度-2℃同时降水量-20%(T-P-)、温度+2℃同时降水量-20%(T+P-)、温度-2℃同时降水量+20%(T-P+)8种气候变化情景.结果显示:贡嘎山峨眉冷杉林土壤CO_2释放随着温度增加而增加,土壤N_2O释放对降水量改变敏感,而土壤NO的释放对温度和降水的改变均比较敏感,二者表现为协同作用.温度+2℃同时降水量+20%(升P+)情景下土壤CO_2释放最高,高于基线情景的36.08%;温度-2℃同时降水量+20%(T-P+)情景下土壤CO_2释放最低,低于基线情景的36.89%.土壤N_2O释放随着降水量的增加而升高,随着降水量减少而降低;温度和降水最同时增加时土壤NO释放均高于单一增加温度或降水量情景,而温度和降水量同时降低时土壤NO释放均低于单一降低温度或降水量情景.     

衡阳紫色土丘陵坡地土壤酶活性对植被恢复的响应

以典型的衡阳紫色土丘陵坡地植被不同恢复阶段为研究对象。采用空间代替时间序列的方法,选用立地条件基本相似的裸荒地、草本群落、灌木群落和乔木群落4种类型表示恢复的4个阶段,通过调查取样和实验分析,探索不同恢复条件下0-10、10-20、20-40 cm土层酶活性的分布特征,以及土壤酶活性对植被恢复的响应。结果表明：1）随着恢复的进行,脲酶、蔗糖酶与碱性磷酸酶活性显著增加（P＜0.05）,过氧化氢酶活性显著减小（P＜0.05）。2）随着土层的加深,脲酶、蔗糖酶与碱性磷酸酶活性显著减小（P＜0.05）,过氧化氢酶活性显著增加（P＜0.05）。3）脲酶、蔗糖酶与碱性磷酸酶之间呈极显著正相关（P＜0.01）,且均与土壤含水量、物理性黏粒、土壤有机碳、全氮、全磷、碱解氮、速效钾、阳离子交换量呈极显著正相关（P＜0.01）,与容重及pH值呈显著或极显著负相关（P＜0.05或P＜0.01）。4）过氧化氢酶与脲酶呈极显著负相关（P＜0.01）,与蔗糖酶与碱性磷酸酶相关性不显著（P＞0.05）,与土壤有机碳、全氮、碱解氮、速效钾及阳离子交换量呈显著或极显著负相关（P＜0.05或P＜0.01）,与 pH 值呈显著正相关（P＜0.05）。5）土壤脲酶、蔗糖酶与碱性磷酸酶可敏感地反映植被过程中土壤质量的变化,植被恢复可改善表层与深层土壤的生物学性质。     

甲醇提取-吹扫捕集-气质联用法快速测定土壤中8种苯系物

采用甲醇提取-吹扫捕集的前处理方法并结合气相色谱-质谱仪来测定土壤样品中的8种苯系物。实验结果表明,8种苯系物在前处理过程中被有效提取出来并被准确定性和定量,对于低浓度样品也具有良好的实验效果。此方法的检出限为0.3～0.8μg/kg,测定下限为1.2～3.2μg/kg。加标低、中、高3种不同质量比的标准物质,经实验分析土壤中8种苯系物相对标准偏差(RSD)为2.1%～6.8%,加标回收率为91.0%～105%,与相关行业标准相比具有一定的优势。     

Effects of different types of biochar on the properties and reactivity of nano zero-valent iron in soil remediation

• Biochar enhanced the mobility and stability of zero-valent iron nanoparticles. • Particle performance was best when the BC:nZVI mass ratio was 1:1. • Bagasse-BC@nZVI removed 66.8% of BDE209. The addition of nano zero-valent iron (nZVI) is a promising technology for the in situ remediation of soil. Unfortunately, the mobility and, consequently, the reactivity of nZVI particles in contaminated areas decrease due to their rapid aggregation. In this study, we determined how nZVI particles can be stabilized using different types of biochar (BC) as a support (BC@nZVI). In addition, we investigated the transport behavior of the synthesized BC@nZVI particles in a column filled with porous media and their effectiveness in the removal of BDE209 (decabromodiphenyl ether) from soil. The characterization results of N₂ Brunauer–Emmett–Teller (BET) surface area analyses, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) indicated that nZVI was successfully loaded into the BC. The sedimentation test results and the experimental breakthrough curves indicated that all of the BC@nZVI composites manifested better stability and mobility than did the bare-nZVI particles, and the transport capacity of the particles increased with increasing flow velocity and porous medium size. Furthermore, the maximum concentrations of the column effluent for bagasse–BC@nZVI (B–BC@nZVI) were 19%, 37% and 48% higher than those for rice straw–BC@nZVI (R–BC@nZVI), wood chips–BC@nZVI (W–BC@nZVI) and corn stalks–BC@nZVI (C–BC@nZVI), respectively. A similar order was found for the removal and debromination efficiency of decabromodiphenyl ether (BDE209) by the aforementioned particles. Overall, the attachment of nZVI particles to BC significantly increased the reactivity, stability and mobility of B–BC@nZVI yielded, and nZVI the best performance.     

Assessment of future climate change impacts on water-heat-salt migration in unsaturated frozen soil using CoupModel

• A model coupling water-heat-salt of unsaturated frozen soil was established. • Future temperature, precipitation, and evaporation increase in freeze–thaw period. • Soil water, heat, and salt transport are closely coupled during freeze–thaw period. • Freeze–thaw cycles and future climate change can exacerbate salinization. The transport mechanisms of water, heat, and salt in unsaturated frozen soil, as well as its response to future climate change are in urgent need of study. In this study, western Jilin Province in north-eastern China was studied to produce a model of coupled water-heat-salt in unsaturated frozen soil using CoupModel. The water, heat, and salt dynamics of unsaturated frozen soil under three representative concentration pathway (RCP) scenarios were simulated to analyze the effects of future climate change on unsaturated frozen soil. The results show that water, heat, and salt migration are tightly coupled, and the soil salt concentration in the surface layer (10 cm) exhibits explosive growth after freezing and thawing. The future (2020–2099) meteorological factors in the study area were predicted using the Statistical Downscaling Model (SDSM). For RCP2.6, RCP4.5, and RCP8.5 scenarios, future temperatures during the freeze–thaw period increased by 2.68°C, 3.18°C, and 4.28°C, respectively; precipitation increased by 30.28 mm, 28.41 mm, and 32.17 mm, respectively; and evaporation increased by 93.57 mm, 106.95 mm, and 130.57 mm, respectively. Climate change will shorten the freeze–thaw period, advance the soil melting time from April to March, and enhance water and salt transport. Compared to the baseline period (1961–2005), future soil salt concentrations at 10 cm increased by 1547.54 mg/L, 1762.86 mg/L, and 1713.66 mg/L under RCP2.6, RCP4.5, and RCP8.5, respectively. The explosive salt accumulation is more obvious. Effective measures should be taken to prevent the salinization of unsaturated frozen soils and address climate change.