Analysis and assessment of heavy metals pollution in soils around a Pb and Zn smelter in Baoji City,Northwest China

Soil heavy metal pollution from mining activities is potentially harmful to human health through the food chain. In this study, a total of 43 soil samples were collected from a depth of 0–20 cm from fields close to a Pb and Zn smelter. The samples were used to: 1) analyze the pollution level of heavy metals (Pb, Zn, Cr, and Cu) and spatial distribution pattern; 2) evaluate the degree of accumulation and enrichment, potential ecological risk, and human health risk; and 3) perform source apportionment in Fengxiang County, Shaanxi Province of China. The results showed that the concentration ranged from 43.67 to 189.55, 131.43 to 239.53, 74.77 to 112.25, and 24.69 to 37.71 mg·kg^?1 for Pb, Zn, Cr, and Cu, respectively, and the mean concentration for Pb, Zn, Cr, and Cu was 129.46, 192.85, 91.98 and 31.67 mg·kg^?1, respectively. The concentrations were greater than the Shaanxi Province background values, while they were lower than the second-level limits of Environmental Quality Standard for Soils of China (EQSS). The spatial distribution of heavy metal contents showed a banded in soil except Cu. The spatial distribution pattern and pollution assessment indexes (I_geo, EF) indicated that the investigated metals had been accumulated in the study areas, and implied significant influences from anthropogenic activities, local meteorological situation, and soil properties. The ecological risk assessment showed that the risks were relatively low (RI<150). Compared with the exposure risk for adults, that for children was significantly greater. The ingestion of heavy metals in the soils by humans was the main exposure pathway compared with the dermal exposure. There may be a risk of noncarcinogenic adverse health effects (HQ < 1, 0.377 ≤ HI≤1.553) on children, but the adults were unlikely to experience obvious adverse health effects (HQ < 1, HI < 1). The carcinogenic risk of Cr for adults and children was at an unacceptable level. The carcinogenic and noncarcinogenic risks were in the order of children > adults. The correlation analysis showed that Pb, Cr, and Cu have identical anthropogenic and natural sources, while Zn has another identical source. This study could provide a basis for the sustainable management of this region by reducing metal inputs and to protect soils from long-term heavy metal accumulation.     

围封与放牧管理对高寒草甸植物功能性状和功能多样性的影响

植物功能性状能够响应生存环境的变化并直接决定着生态系统功能。为了揭示围封与放牧管理对物种共存和驱动群落构建的影响机理,该研究以青藏高原东缘高寒草甸为对象,分析了围封与放牧处理对植物功能性状和功能多样性的影响。结果显示:(1)在群落水平,放牧显著降低了比叶面积和植物高度;在物种水平,放牧群落中多数杂类草比叶面积减小,而莎草类和禾草类的比叶面积在处理间无显著差异。(2)叶干物质含量与比叶面积在围封和放牧处理中均呈显著负相关关系,在放牧处理中,叶干物质含量与植物高度呈显著的二次函数关系,即随着叶干物质含量的增大,植物高度先减小后增大;在同等比叶面积的情况下,与围封相比,放牧降低了叶干物质含量;在相同叶干物质含量的情况下,与围封相比,放牧降低了植物高度。(3)放牧在总体上降低了种间性状的平均差异,植物性状表现出趋同响应,具体表现为放牧减小了叶干物质含量和植物高度的种间差异;与围封相比,放牧显著提高了功能均匀度,减小了功能分离度。研究表明,不同植物种对放牧的响应模式存在差异,放牧降低了种间对光资源的竞争,可能增加了对土壤养分的竞争,放牧驱动群落构建的过程中,土壤养分是非常重要的作用因子,说明放牧影响物种共存依赖于对多种资源的竞争。     

Chitin binding by Thermobifida fusca cellulase catalytic domains

Cellulose is a linear homopolymer of beta 1-4 linked glucose residues. Chitin is similar to cellulose in structure, and can be described as cellulose with the hydroxyl group on the C2 carbon replaced by an acetylamine group. Both cellulose and chitin form tightly packed, extensively hydrogen-bonded micro-fibrils. Up to now, binding of cellulase catalytic domains (CDs) to chitin has not been reported. In this article, binding of the CDs of Thermobifida fusca Cel6A, Cel6B, Cel48A, Cel5A, and Cel9A to alpha-chitin was investigated. The CDs of endocellulases, Cel6A and Cel5A did not bind to alpha-chitin; one exocellulase, Cel48A CD bound alpha-chitin moderately well; and the exocellulase Cel6B CD and the processive endocellulase Cel9A CD bound extremely tightly to alpha-chitin. Only mutations of Cel6B W329C, W332A and G234S and Cel9A Y206F, Y206S and D261A/R378K caused weaker binding to alpha-chitin than wild-type, and all these mutations were of residues near the catalytic center. One mutant enzyme, Cel9A D261A/R378K had weak chitinase activity, but no soluble products were detected. Chitotriose and chitotetraose were docked successfully to the catalytic cleft of Cel9A. In general, the positioning of the sugar residues in the model structures matched the cellooligosaccharides in the X-ray structure. Our results show that the binding of chitin by a cellulase can provide additional information about its binding to cellulose.     

Magnetic susceptibilities of lake sediment and soils on the shoreline of Lake Naivasha,Kenya

On steep, unvegetated slopes, sands (particle sizes 0.063 to 2 mm) and gravels (2–64 mm) erode from the shoreline of Lake Naivasha (Kenya) and enter the lake basin. This occurred freely where fringing papyrus (Cyperus papyrus) swamp had been cleared in favour of landing jetties or agriculture. Gravel-sized particles have been recovered up to 60 m offshore and sands to 80 m. In an area where papyrus was undisturbed and the swamp margin was 52 m wide, gravel did not enter the lake and sands penetrated to around 35 m. Large particles are much easier to trace to source and to manage than the finer silts and clays (<0.63 m) that form the bulk of Lake Naivasha's sediment. The pattern of mass specific magnetic susceptibilities for the <63 m fraction of lake sediment around the southern shoreline of the lake suggests that fine particles enter open water directly from the shoreline and are not transported from the lake's only perennial inflow, the River Malewa in the north. Such particles originate from a hinterland that supports high intensity horticulture and are therefore a potential source of contamination. Mean ± SD susceptibility (_If) immediately offshore papyrus fringe was 0.49 ± 0.08 × 10^-6 m³ kg^-1 compared with higher values of 1.33 ± 0.14 × 10^-6 m³ kg^-1 where there was no papyrus barrier (P<0.0001). The value for five sites in the middle parts of the lake was 0.45 ± 0.02 × 10^-6 m³ kg^-1 with 1.38 ± 0.10 × 10^-6 m³ kg^-1 near the mouth of the River Malewa. The results of this study are evidence, therefore, that conservation of a continuous papyrus margin of about 50 m width is a priority for intercepting particulate material.     

云南热带地区土壤中的暗色丝孢菌初查

从云南西双版纳及河口热带雨林、植物园、荒坡和农田中采集混合土壤样品30余份,采用稀释平板法和土壤颗粒法从中分离获得暗色丝孢菌分离物53个,经形态鉴定分属于29属37种。其中4个为中国新记录种：尼尔布洛孢Bloxamia nilagirica、不规头梗孢Cephaliophora irregularis、单梗粘孢Haplographium delicatum和不列颠黑团孢Periconia britannica,对它们进行了描述和必要的讨论。研究过的标本（干制培养物）及活菌种保存在山东农业大学植物病理学标本室（HSAUP）。     

哀牢山常绿阔叶林水源涵养功能及其在应对西南干旱中的作用

为了解云南哀牢山中山湿性常绿阔叶林在2010年初西南地区特大干旱中是否遭遇水分胁迫,及其水源涵养功能在应对干旱中的作用,测定了该森林土壤和主要树种在2010年旱季的水分状况,并对比研究了原生林和森林经砍伐烧垦后形成的毛蕨菜-玉山竹群丛的土壤持水、凋落物持水、水面蒸发和土壤水分季节动态。结果表明:常绿阔叶林主要树种在2010年初西南特大干旱中并未遭受水分胁迫(最旱月叶片凌晨水势高于-0.4 MPa)。虽然常绿阔叶林土壤含水量和地下水位在最旱月都达到了有观测以来的最低点,但主要根系分布区的土壤水势仍不低于-0.5 MPa,并高于毛蕨菜-玉山竹群丛。森林较好的水分状况和原生常绿阔叶林较好的水源涵养功能有关。常绿阔叶林的土壤总持水量尤其是非毛管持水量要显著大于毛蕨菜-玉山竹群丛,同时也大于云南地区的一些次生林和人工林。常绿阔叶林地表丰富的凋落物通过持水和抑制土壤蒸发也对水源涵养有一定作用。哀牢山常绿阔叶林良好的水源涵养功能,充足的土壤地下水储存弥补了旱季和特大干旱中降水的不足。结果指示原生林在水源涵养中不可替代的作用,以及加强原生林保护在提高区域抗干旱能力中的重要意义。     

Tree diversity,tree height and environmental harshness in eastern and western North America

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co‐varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.     

Genetic diversity and structure among natural populations of Sindora glabra in Hainan Island,China as revealed by ISSR markers

Sindora glabra, one of the second-class national protective plants in China, has important ecological and commercial values. To understand the genetic diversity and structure of S. glabra, eleven natural populations from four areas of Hainan Island in China were analyzed by inter-simple sequence repeat (ISSR) markers. Thirteen primers were screened out and used to amplify 157 DNA samples. A total of 122 bands were obtained, among which 114 (93.4%) bands were polymorphic. Genetic parameters including average number of effective alleles (1.547), Nei's gene diversity (0.321), Shannon's information index (0.482), and gene differentiation coefficient (0.1944) revealed a high level of genetic diversity maintained in S. glabra populations. The variation within populations accounted for 85.6% of total variation based on analysis of molecular variance. Genetic distance analysis showed that 11 populations could be divided into three groups and populations from the same areas were classified as one group, suggesting that high genetic diversity of S. glabra was attributable to geographic isolation. Together, introduction of germplasm from distant natural distribution areas would be a sound strategy for germplasm resource conservation of S. glabra and selection of elite individuals from populations of far relationship for hybridization is of great importance for breeding improvement programs in future.     

Soil carbon dynamics in a Pinus massoniana plantation following clear-cutting and slash removal

Aims Slash removal is a common practice to prepare recently harvested sites for replanting. However, little is known about its impact on soil carbon (C) dynamics in subtropical plantations. This study evaluates the effects of burning versus manual slash removal site preparation treatments on soil organic carbon (SOC), soil respiration and soil microbial community structure in a Pinus massoniana plantation in southern China.Methods Three areas within a mature P. massoniana plantation were clearcut. Two months following harvesting, slash on one-half of each area was burned (BURN), whereas slash was manually removed (MANR) on the other portion. Slash removal treatments were also compared with adjacent uncut plantation areas (UNCUT). Soil samples, and soil respiration measurements were used to characterize soil properties and microbial communities following slash removal treatments. Important findings Mean soil respiration rates from the MANR and BURN treatments were 26% and 17% lower, respectively, than the UNCUT treatment over 1 year. The MANR and BURN treatment resulted in soils with 27% and 9% reduction in total phospholipid fatty acids (PLFAs) and 18% and 10% reduction in bacterial PLFAs, respectively, compared with the UNCUT treatment. However, no significant differences existed between slash removal treatments with respect to soil chemical properties, SOC chemical compositions, soil respiration and microbial communities; although PLFA patterns were notably different for the burned plots. Most factors affecting C dynamics and microbial communities were not sensitive to the differences imparted to the ecosystem due to manual slash removal or burning. Our results suggested that low-intensity burning after clear-cutting might have no significant effect on soil C pool and its dynamics compared with manual slash removal in subtropical plantations.