Aluminum toxicity in forests exposed to acidic deposition: The ALBIOS results     

Christopher S. Cronan  Richard April  Richmond J. Bartlett  Paul R. Bloom  Charles T. Driscoll  Steven A. Gherini  Gray S. Henderson  J. D. Joslin  J. M. Kelly  Roderic A. Parnell  Howard H. Patterson  Dudley J. Raynal  Michail Schaedle  Carl L. Schofield  Edward I. Sucoff  Herbert B. Tepper  Frank C. Thornton 《Water, air, and soil pollution》1989,48(1-2):181-192

The ALBIOS project was conducted to examine the influence of acidic deposition on aluminum transport and toxicity in forested ecosystems of eastern North America and northern Europe. Patterns of aluminum chemistry were evaluated in 14 representative watersheds exposed to different levels of sulfur deposition. Controlled studies with solution and soil culture methods were used to test interspecific differences in aluminum sensitivity for one indicator species (honeylocust - Gleditsia triacanthos L. ) and six commercial tree species (red spruce - Picea rubens Sarg., red oak - Quercus rubra L., sugar maple - Acer saccharum Marsh., American beech - Fagus grandifolia Ehrh., European beech - Fagus sylvatica, and loblolly pine - Pinus Taeda L. ). Overall, red spruce was the tree species whose growth was most sensitive to soluble aluminum, with significant biomass reductions occurring at Al concentrations of approximately 200–250 umol/L. Analyses of soil solutions from the field sites indicated that the conditions for aluminum toxicity for some species exist at some of the study areas. At these watersheds, aluminum toxicity could act as a contributing stress factor affecting forest growth.  相似文献   

The role of dissolved organic carbon in the chemistry and bioavailability of mercury in remote Adirondack lakes   总被引：1，自引：0，他引：1  

C. T. Driscoll  V. Blette  C. Yan  C. L. Schofield  R. Munson  J. Holsapple 《Water, air, and soil pollution》1995,80(1-4):499-508

A number of recent studies have documented elevated concentrations of mercury (Hg) in fish caught in remote lakes and a pattern of increased concentrations of Hg in fish tissue with decreasing water column pH. Because of the potential linkage between fish Hg and surface water acidification, factors regulating water column concentrations and bioavailability of Hg were investigated in Adirondack lakes through a field study and application of the Mercury Cycling Model (MCM). Concentrations of total Hg and total MeHg were highly variable, with concentrations of total MeHg about 10% of total Hg in lakes which did not show anoxic conditions. In lakes exhibiting anoxic conditions in the hypolimnion during summer stratification, concentrations of total MeHg were elevated. Concentrations of total Hg and total MeHg increased with decreasing pH in remote Adirondack lakes. However, more importantly, concentrations of total Hg and total MeHg increased with increasing concentrations of dissolved organic carbon (DOC) and percent near-shore wetlands in the drainage basin. Mercury concentrations in muscle tissue of yellow perch from Adirondack lakes were elevated above the U.S. FDA action level (1 μg/g Hg) in 7% of the fish sampled or in one or more individual fish from 9 of the 16 lakes sampled. Fish Hg concentrations generally increased with increasing fish length, weight and age. Patterns of increasing Hg concentration with age likely reflect shifts in prey of yellow perch and the bioconcentration of Hg along the food chain. For age 3 to 5 perch, concentrations of Hg increased with increasing concentrations of DOC and percent near-shore wetlands in the drainage basin. However, for a lake with very high DOC concentrations, fish concentrations of Hg declined. Calculations with the MCM also show that concentrations of Hg species increase with increasing DOC due to complexation reactions. Increases in DOC result in increasing concentrations of Hg in biota but decreases in the bioconcentration factor of Hg in fish tissue. This research suggests that DOC is important in the transport of Hg to lake systems. High concentrations of DOC may complex MeHg, diminishing its bioavailability. At high concentrations of monomeric Al, the complexation of MeHg with DOC apparently decreases, enhancing the bioavailability of MeHg.  相似文献   

Infrared remote sounding of the middle atmosphere of venus from the pioneer orbiter     

Taylor FW  Diner DJ  Elson LS  Hanner MS  McCleese DJ  Martonchik JV  Reichley PE  Houghton JT  Delderfield J  Schofield JT  Bradley SE  Ingersoll AP 《Science (New York, N.Y.)》1979,203(4382):779-781

Orbiter infrared measurements of the Venus atmosphere in the 60- to 140-kilometer region show very small diurnal temperature differences near the cloud tops, increasing somewhat at higher levels. The seasonal (that is, equator to pole) contrasts are an order of magnitude larger, and the temperatures unexpectedly increase with increasing latitude below 80 kilometers. An isothermal layer at least two scale heights in vertical extent is found near the 100-kilometer altitude, where the temperature is about 175 K. Structure is present in the cloud temperature maps on a range of spatial scales. The most striking is at high latitude, where contrasts of nearly 50 K are observed between a cold circumpolar band and the region near the pole itself.  相似文献   

The evolution of modern eukaryotic phytoplankton   总被引：1，自引：0，他引：1  

Falkowski PG  Katz ME  Knoll AH  Quigg A  Raven JA  Schofield O  Taylor FJ 《Science (New York, N.Y.)》2004,305(5682):354-360

The community structure and ecological function of contemporary marine ecosystems are critically dependent on eukaryotic phytoplankton. Although numerically inferior to cyanobacteria, these organisms are responsible for the majority of the flux of organic matter to higher trophic levels and the ocean interior. Photosynthetic eukaryotes evolved more than 1.5 billion years ago in the Proterozoic oceans. However, it was not until the Mesozoic Era (251 to 65 million years ago) that the three principal phytoplankton clades that would come to dominate the modern seas rose to ecological prominence. In contrast to their pioneering predecessors, the dinoflagellates, coccolithophores, and diatoms all contain plastids derived from an ancestral red alga by secondary symbiosis. Here we examine the geological, geochemical, and biological processes that contributed to the rise of these three, distantly related, phytoplankton groups.  相似文献   

The effect of heat on wheat gluten and the involvement of sulphydryl-disulphide interchange reactions     

J.D. Schofield  R.C. Bottomley  M.F. Timms  M.R. Booth 《Journal of Cereal Science》1983,1(4):241-253

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Effects of Restricted Water Availability and Increased Temperature on the Grain Filling, Drying and Quality of Winter Wheat   总被引：1，自引：0，他引：1  

M. J. Gooding  R. H. Ellis  P. R. Shewry  J. D. Schofield 《Journal of Cereal Science》2003,37(3):295-309

Experiments in controlled environments examined the effects of the timing and severity of drought, and increased temperature, on grain development of Hereward winter wheat. Environmental effects on grain specific weight, protein content, Hagberg Falling Number, SDS-sedimentation volume, and sulphur content were also studied. Drought and increased temperature applied before the end of grain filling shortened the grain filling period and reduced grain yield, mean grain weight and specific weight. Grain filling was most severely affected by drought between days 1–14 after anthesis. Protein content was increased by stresses before the end of grain growth, because nitrogen harvest index was less severely affected than was dry matter harvest index. Hagberg Falling Number was increased to the greatest extent by stresses applied 15–28 days after anthesis. Treatment effects on grain sulphur content were similar to those on protein content, such that N:S ratio was not significantly affected by drought nor temperature stresses. The effects of restricted water on grain yield and quality were linearly related to soil moisture between 44 and about 73% field capacity (FC) from days 15–28. Drought stress (but not temperature stress) before the end of grain filling decreased SDS-sedimentation volume relative to drought applied later.  相似文献   

A unified capture-recapture framework     

Matthew R. Schofield  Richard J. Barker 《Journal of Agricultural, Biological & Environmental Statistics》2008,13(4):458-477

This article develops a hierarchical framework for capture-recapture data that separates the capture process from the demographic processes of interest, such as birth and survival. This allows users to parameterize in terms of meaningful demographic parameters. The framework is very flexible with many of the current capture-recapture models included as special cases. The hierarchical nature of the model allows natural expression of relationships, both between parameters and between parameters and the realization of random variables, such as population size. Previously, many of these relationships, such as density dependence have been unable to be explored using capture-recapture data. Density dependence, where survival and birth rates depend on the population size, is an interesting special case. We fit a density-dependent model to male Gonodontis bidentata data and report evidence of negative density dependence in percapita birth rates and weak evidence of negative density dependence in survival.  相似文献   

Dynamic Viscoelastic Behavior of High-Pressure-Treated Wheat Gluten     

A. Apichartsrangkoon  A. E. Bell  D. A. Ledward  J. D. Schofield 《Cereal Chemistry》1999,76(5):777-782

The effects on the viscoelastic behavior of hydrated wheat gluten after treatment at different pressures (200–800 MPa), temperatures (20, 40, and 60°C), and holding times (20 and 50 min) were investigated by controlled stress rheometry. Because of the wide range of properties, four different torque amplitudes were used (0.5, 1.00, 3.00, and 6.00 mNm). Significant effects on rheological properties were observed, except when samples were analyzed at 0.5 mNm (limited heat and pressure treatments). Both storage modulus (G′) and loss modulus (G″) were more affected by temperature than pressure. The holding time had substantial effect on the slopes of both moduli at mild treatments; for the more severe treatments, the intercepts of the storage moduli in particular were extensively affected.  相似文献   

Isolation of Polar Lipid Classes from Wheat Flour Extracts by Preparative High‐Performance Liquid Chromatography     

Eleni Papantoniou  Eugene W. Hammond  Fiona Scriven  Michael H. Gordon  J. David Schofield 《Cereal Chemistry》2001,78(6):663-665

A preparative high‐performance liquid chromatographic method was developed for the isolation of polar lipid classes of mono‐ and digalactosyldiacylglycerols (MGDG and DGDG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylcholine (PC) from wheat flour lipid extracts in relatively large quantities. The method allowed the separation of ≤100 mg/injection of lipid mixture. MGDG, DGDG, and PC were isolated as pure lipid classes, whereas PE was isolated in a mixture with PG, PC, and lysophosphatidylcholine (LPC). The availability of this methodology will facilitate research aimed at investigating the functional role of such lipids in foods.  相似文献   

Stress Relaxation Behavior of Wheat Dough,Gluten, and Gluten Protein Fractions     

W. Li  B. J. Dobraszczyk  J. D. Schofield 《Cereal Chemistry》2003,80(3):333-338

Relaxation behavior was measured for dough, gluten and gluten protein fractions obtained from the U.K. biscuitmaking flour, Riband, and the U.K. breadmaking flour, Hereward. The relaxation spectrum, in which relaxation times (τ) are related to polymer molecular size, for dough showed a broad molecular size distribution, with two relaxation processes: a major peak at short times and a second peak at times longer than 10 sec, which is thought to correspond to network structure, and which may be attributed to entanglements and physical cross‐links of polymers. Relaxation spectra of glutens were similar to those for the corresponding doughs from both flours. Hereward gluten clearly showed a much more pronounced second peak in relaxation spectrum and higher relaxation modulus than Riband gluten at the same water content. In the gluten protein fractions, gliadin and acetic acid soluble glutenin only showed the first relaxation process, but gel protein clearly showed both the first and second relaxation processes. The results show that the relaxation properties of dough depend on its gluten protein and that gel protein is responsible for the network structure for dough and gluten.  相似文献