Effects of elevated CO2, nitrogen supply and tropospheric ozone on spring wheat-II. Nutrients (N, P, K, S, Ca, Mg, Fe, Mn, Zn)

CO(2) enrichment is expected to alter leaf demand for nitrogen and phosphorus in plant species with C(3) carbon dioxide fixation pathway, thus possibly causing nutrient imbalances in the tissues and disturbance of distribution and redistribution patterns within the plants. To test the influence of CO(2) enrichment and elevated tropospheric ozone in combination with different nitrogen supply, spring wheat (Tritium aestivum L. cv. Minaret) was exposed to three levels of CO(2) (361, 523, and 639 microl litre(-1), 24 h mean from sowing to final harvest), two levels of ozone (28.4 and 51.3 nl litre(-1)) and two levels of nitrogen supply (150 and 270 kg ha(-1)) in a full-factorial design in open-top field chambers. Additional fertilization experiments (120, 210, and 330 kg N ha(-1)) were carried out at low and high CO(2) levels. Macronutrients (N, P, K, S, Ca, Mg) and three micronutrients (Mn, Fe, Zn) were analysed in samples obtained at three different developmental stages: beginning of shoot elongation, anthesis, and ripening. At each harvest, plant samples were separated into different organs (green and senescent leaves, stem sections, ears, grains). According to analyses of tissue concentrations at the beginning of shoot elongation, the plants were sufficiently equipped with nutrients. Elevated ozone levels neither affected tissue concentrations nor shoot uptake of the nutrients. CO(2) and nitrogen treatments affected nutrient uptake, distribution and redistribution in a complex manner. CO(2) enrichment increased nitrogen-use efficiency and caused a lower demand for nitrogen in green tissues which was reflected in a decrease of critical nitrogen concentrations, lower leaf nitrogen concentrations and lower nitrogen pools in the leaves. Since grain nitrogen uptake during grain filling depended completely on redistribution from vegetative pools in green tissues, grain nitrogen concentrations fell considerably with severe implications for grain quality. Ca, S, Mg and Zn in green tissues were influenced by CO(2) enrichment in a similar manner to nitrogen. Phosphorus concentrations in green tissues, on the other hand, were not, or only slightly, affected by elevated CO(2). In stems, 'dilution' of all nutrients except manganese was observed, caused by the huge accumulation of water soluble carbohydrates, mainly fructans, in these tissues under CO(2) enrichment. Whole shoot uptake was either remarkably increased (K, Mn, P, Mg), nearly unaffected (N, S, Fe, Zn) or decreased (Ca) under CO(2) enrichment. Thus, nutrient cycling in plant-soil systems is expected to be altered under CO(2) enrichment.     

Assessment of trace metal distribution and contamination in surface soils of Hong Kong

An intensive investigation was conducted to study the distribution of trace metals in surface soils of Hong Kong and to assess the soil environmental quality. From results of cluster analysis, and comparisons among soil types and areas, it is clearly shown that increases in trace metal concentrations in the soils were generally extensive and obvious in urban and orchard soils, less so in vegetable soils, whilst rural and forest soils were subjected to the least impact of anthropogenic sources of trace metals. However, some of the forest soils also contained elevated levels of As, Cu, and Pb. Urban soils in Hong Kong were heavily polluted by Pb from gasoline combustion. Agricultural soils, both orchard and vegetable soils, usually accumulated As, Cd, Cu, and Zn originating from applications of pesticides, animal manures, and fertilizers. In general, trace metal pollution in soils of the industrial areas and Pb pollution in the soils of the commercial and residential areas were obvious.     

Three-fluid retention in porous media involving water, PCE and air

A classical way to obtain three-fluid retention curves in porous media from measured two-fluid retention curves is based on the Leverett concept, which states that the total volumetric liquid content in a water-wet porous medium, containing water, a nonaqueous-phase liquid (NAPL) and air, is a function of the capillary pressure across the interface between the continuous NAPL and air. This functional relationship results from the assumed condition that in a three-fluid porous medium, the intermediate wetting fluid spreads over the water-air interface. Application of Leverett's concept may not be valid, however, for nonspreading NAPLs like perchloroethylene (PCE). This paper discusses measurements of both PCE-air and water-PCE-air retention curves using a long vertical column in conjunction with a dual-energy gamma radiation system. The data indicate that the Leverett concept was applicable only until a critical PCE saturation had been reached.     

A laboratory exposure procedure for screening pulp and paper mill effluents for the potential of causing increased mixed function oxidase activity in fish

To better understand the relationships between pulp manufacturing processes and mixed function oxidase (MFO) enzyme induction in fish, a practical and standardized exposure procedure is required. This study was undertaken to develop a laboratory-based exposure procedure to quantify the relative MFO induction potencies of different types of pulp and paper mill effluents. One major consideration in developing the procedure was to ensure that the protocol was practical so that tests could be performed in a short time, with small volumes of effluents and using simple experimental conditions. A series of concentration-response and time-course experiments were conducted to find the minimum time and effluent concentration which could distinguish the ability of different effluents to cause significant MFO induction in rainbow trout in the laboratory. Experiments were also conducted to determine the effects of biotic and abiotic factors such as loading density, fish size and feeding regime. This study showed that the exposure of rainbow trout in the laboratory to 10% concentration of secondary-treated effluent for 96 h caused significant increases in hepatic MFO activity. The magnitude of MFO induction was comparable to other field and laboratory observations. While fish size, loading density and feeding regime were found to affect the test results, consistent responses within a laboratory using this protocol are possible, provided that these factors are standardized. Therefore, the short-term exposure approach described in this paper could be a relevant tool for assessing the ability of different types of pulp and paper mill effluents to cause MFO induction in fish.     

多配位基螯合离子交换纤维的研究及其进展

离子交换纤锥作为具有高吸附佐的吸附材料，在金属离子的分离、富集、回收等方面，以及在水净处理净化处理领域得到了迅速的发展及应用，引起了人们的极大兴趣。本文对近十几年来离子交换纤维的合成方法路线、性能研究以及在痕量元素的分离、富集和水处理方面的应用进行了综述，并对目前离子交换纤维的研究中存在的问题提出了一些看法。     

Organic carbon concentration profiles in recent cave sediments: records of agricultural pollution or diagenesis?

Recent (<7 years old) cave sediments in Speedwell Cavern, Derbyshire, show an approximately exponential decay of organic carbon with depth. This phenomenon was thought to be due to one of two causes: (i) changing agricultural practice within the catchment feeding the cave, especially the increased use of sewage sludge and animal slurry as fertilizer; (ii) a relatively constant organic carbon concentration over time in the input sediment, with subsequent carbon mineralization during diagenesis. Carbon isotope composition of the organic material and the evolution of H/C ratio with depth indicate that the latter hypothesis is correct and that the profiles result from microbial diagenesis, not increased organic carbon inputs. By comparison with sediment of known (7 years) age, temporal decay constants for organic matter can be derived; these lie between rates previously determined for organic matter decomposition in marine sediments and soils. The H/C ratio of organic matter can be modelled as a function of time and proceeds in a similar fashion to soil organic material.     

Effect of ozone on net photosynthesis in oat (Avena sativa) and duckweed (Lemna gibba)

Short exposure to ozone depressed photosynthesis in both oat and duckweed at concentrations above 140 microg m(-3) and 300 microg m(-3), respectively. The effect on exposed oat flag leaves was age-dependent, with maximum susceptibility to ozone 10-20 days after emergence of the panicle. In duckweed, photosynthesis was more sensitive to differences in ozone concentration than to differences in duration of exposure.