Distribution characteristics and influencing factors of soil organic carbon in alpine ecosystems on the Tibetan Plateau transect, China

The undisturbed regions along the Qinghai-Tibet Highway crossing the natural zones of montane desert, alpine meadow-steppe, and montane shrub-coniferous forest were chosen as the study areas. Soil samples were collected at 23 sites and the relations between the influencing factors and distribution of soil organic carbon (SOC) content were studied. The results indicated that the order of SOC content for the whole soil profile with different vegetations and in the horizontal direction was shown as below: forest>shrub>meadow>steppe>desert. All the SOC contents of the top 10 cm soil layers of forest, shrub and meadow vegetations, as well as that of the top 20 cm soil layers in steppe, in the vertical direction, were higher than those of corresponding lower soil layers. However, the SOC content in the desert soil was in accordance. The grey correlative analysis between the climatic factors and SOC content in the top soil show that precipitation was the dominant climatic factor affecting the distribution of SOC in the Tibetan Plateau transect. The influence of precipitation on the horizontal distribution of SOC decreased with the increase of precipitation in the horizontal direction. The vertical distribution of SOC along the soil profile was greatly affected by precipitation or the soil clay content in top soil layers, and was clearly influenced by soil silt content or sand content in lower soil layers, as well. The influences of both soil bulk density and soil pH on the vertical distribution of SOC along the soil profile gradually declined. The plant biomass was the most important biotic factors affecting the distribution of the SOC. __________ Translated from Journal of Zhejiang University (Agriculture & Life Sciences), 2007, 33(4): 443–449 [译自: 浙江大学学报(农业与生命科学版)]     

Long-term cultivation impact on the heavy metal behavior in a reclaimed wetland,Northeast China

Purpose

Heavy metal fractionation varies according to land uses. To understand the behavior of heavy metals in wetland soils under long-term agricultural cultivation, we examined the distribution, source, and associated environmental risk of heavy metals in different types of wetland soils.

Materials and methods

Soils were collected in cultivated lands, artificial ditches, and riparian zones from a reclaimed wetland in the Sanjiang Plain, Northeast China. They were analyzed for total concentrations and chemical fractions of Pb, Cd, Cu, Zn, Cr, and Ni, as well as pH, soil organic matter, total phosphorus, and particle size distribution.

Results and discussion

Heavy metal concentrations were significantly lower in cultivated wetland than in ditch and riparian wetlands. Riparian wetland was found to exhibit the highest metal concentrations. When compared with other two wetland types, the cultivated wetland showed much higher partitioning levels of heavy metals in the acid-soluble fraction and lower partitioning levels in the oxidizable fraction. Although Cr, Cu, and Ni in ditch and riparian wetlands were identified as the metal pollutants of primary concern, they had a low or no risk of further dispersion to other environmental components. Weathering of parent materials was the main source of Cr and Cu, Pb, Cd, and Zn originated mainly from agricultural practices, and Ni emanated from a mixture of sources.

Conclusions

Long-term agricultural cultivation can lead to significant heavy metal loss in cultivated wetland but enrich heavy metal concentrations in ditch and riparian wetlands. Periodic ditch dredging is considered an effective measure for decreasing heavy metal input into the fluvial system and thereby reducing the dispersion to the regional water environment.     

不同种植间距对香根草植物边坡优先流发育特征的影响

[目的]分析优先流在香根草边坡中的发育特征,研究植物根系与优先流之间的关系,为进一步研究降雨条件下植物根系对边坡土体稳定性的影响提供理论依据。[方法]以种植间距为50 cm和10 cm的香根草为研究对象,模拟30 mm和50 mm两种不同的降雨量,采用示踪剂试验研究了香根草边坡土壤的优先流发育特征。[结果]香根草种植间距从50 cm减少到10 cm会增大边坡的水力响应。在50 mm的降雨量作用下,10 cm种植间距的香根草边坡土壤的染色面积比率和优先流比分别是50 cm的1.55,1.76倍。表层土0—10 cm土层深度范围内染色路径数量变化不明显,在10—35 cm深度土层范围,10 cm种植间距的染色路径数量多于50 cm种植间距的香根草边坡土壤。当降雨量由30 mm增加至50 mm时,水流会通过优势通道更迅速迁移到边坡土壤中。降雨量为30 mm土壤的染色面积比率(36.11%)和优先流比(67.25%)小于50 mm土壤的染色面积比率(49.68%)和优先流比(79.96%),并且染色路径数量随着降雨量的增加而增多。[结论]香根草根系特征与优先流关系密切。选择植物护坡时,应合理选...     

GC-MS鉴定叶绿素皂化母液提取物

本文报道GC-MS鉴定莫合烟叶叶绿素皂化母液提取物。分离出75个组份,鉴定其中主要组份为叶绿醇,含量13.18％;十六碳醛,含量11.52％;6,10,14-三甲基-2-十五酮,含量6.24％;3-甲基戊酸乙酯,含量5.05％;1-甲基戊苯,含量2.96％;9,12,15-十八碳三烯酸乙酯,磷量2.03％,叶绿醇、十六碳醛,6,10,14-三甲基-2-十五酮和十八碳三烯酸乙酯均有利用价值。     

Atomically resolved single-walled carbon nanotube intramolecular junctions

Intramolecular junctions in single-walled carbon nanotubes are potentially ideal structures for building robust, molecular-scale electronics but have only been studied theoretically at the atomic level. Scanning tunneling microscopy was used to determine the atomic structure and electronic properties of such junctions in single-walled nanotube samples. Metal-semiconductor junctions are found to exhibit an electronically sharp interface without localized junction states, whereas a more diffuse interface and low-energy states are found in metal-metal junctions. Tight-binding calculations for models based on observed atomic structures show good agreement with spectroscopy and provide insight into the topological defects forming intramolecular junctions. These studies have important implications for applications of present materials and provide a means for assessing efforts designed to tailor intramolecular junctions for nanoelectronics.     

红鳞蒲桃苗木生长和生理生化特征对不同盐分和干旱胁迫的响应

以1年生红鳞蒲桃盆栽苗木为研究对象,设置不同盐胁迫浓度及干旱程度,研究盐旱交互作用对红鳞蒲桃苗木的高、地径生长和各项生理指标的影响。结果表明：干旱和盐胁迫都抑制了红鳞蒲桃的生长,盐胁迫的影响要大于干旱胁迫,高生长受到的限制大于地径生长,2 g/kg盐分浓度在水分充足条件下促进了地径生长。相对电导率和丙二醛含量均随着干旱和盐胁迫的增强而增大。不同盐分浓度下,干旱胁迫对相对电导率的影响趋势一致,不同盐分胁迫的影响差异不显著。高盐浓度下丙二醛含量的增加显著大于低盐浓度,表明盐胁迫对红鳞蒲桃的伤害更大;红鳞蒲桃的渗透调节物质在干旱和盐交互胁迫下有一定程度的提高。水分充足时,盐分浓度的变化没有对红鳞蒲桃的游离脯氨酸含量产生影响。随着胁迫的增加,渗透调节能力显著提高。低盐浓度下,抗氧化酶活性在水分充足时没有受到显著影响,高盐浓度下,随着干旱胁迫的加剧则显著提高。     

镁基碱金属二元合金热力学性质的理论计算

本文运用Ｍｉｅｄｅｍａ理论，系统地计算了镁与碱金属组成的二元合金系统的液态混和焓和固态合金形成焓。根据理想溶液理论，还计算了Ｌｉ－Ｍｇ系统在１０００Ｋ时的熵、以及自由能－成分曲线，所得的结果同已有的实验结果和第一原理赝势方法计算的结果符合得比较好。     

A STELLA model for the estimation of atrazine runoff,leaching, adsorption,and degradation from an agricultural land

Background, aim, and scope  

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is one of the most widely used herbicides for broadleaf weed and certain annual grass controls and is popular because of its effectiveness and low cost. Losses of atrazine from agricultural lands into adjacent surface water and underlying groundwater have raised public concerns. Several computer models have been developed for atrazine runoff in watersheds. One limitation for most of these models, however, is that vast amounts of input parameters are required for simulations. These input parameters are sometimes difficult to obtain through the experimental measurements for model calibrations, validations, and applications. Therefore, a need exists to develop a simple and yet a realistic modeling tool that can be used for effectively investigating atrazine dynamics in agricultural soils. This study was designed to meet this need.     

强非线性水平混沌振动台

该文研究了一种水平混沌振动台,机构的运动微分方程是强非线性的,数值仿真和实验结果表明,该振动台的动态响应是混沌的,且敏感依赖于初始条件。     

How different reforestation approaches affect red soil properties in southern China

Significant differences were found in soil physicochemical and biological effects between various forest restoration approaches of a hilly red‐soil region, southern China. Soil quality was the highest in natural secondary forest (0·95), while in sites revegetated with tea‐oil camellia (Camellia oleifera), Chinese fir (Cunninghamia lanceolata) and slash pine (Pinus elliottii) and control sites, integrated soil quality indices were 0·68, 0·55, 0·36 and 0·04 respectively. The lower soil quality of plantations and controls resulted from increased disruption of soil physical structure, lower quality litter fall, lower litter fall production, reduction in microbial biomass, decline of microbial function and loss of soil nutrients due to periodically artificial tending and accelerated soil erosion. Improvement in soil physicochemical properties and enhanced soil microbial function at a natural secondary forest site demonstrated the inherent restoration of these soils. Hence, natural restoration, as well as reducing human disturbance, is a better approach to improving soil properties than returning farmland to planted woodlands. Copyright © 2005 John Wiley & Sons, Ltd.