Temperature, water content and wet-dry cycle effects on DOC production and carbon mineralization in agricultural peat soils     

Alex T. Chow  Kenneth K. Tanji  Randy A. Dahlgren 《Soil biology & biochemistry》2006,38(3):477-488

Agricultural peat soils in the Sacramento-San Joaquin Delta, California have been identified as an important source of dissolved organic carbon (DOC) and trihalomethane precursors in waters exported for drinking. The objectives of this study were to examine the primary sources of DOC from soil profiles (surface vs. subsurface), factors (temperature, soil water content and wet-dry cycles) controlling DOC production, and the relationship between C mineralization and DOC concentration in cultivated peat soils. Surface and subsurface peat soils were incubated for 60 d under a range of temperature (10, 20, and 30 °C) and soil water contents (0.3-10.0 g-water g-soil⁻¹). Both CO₂-C and DOC were monitored during the incubation period. Results showed that significant amount of DOC was produced only in the surface soil under constantly flooded conditions or flooding/non-flooding cycles. The DOC production was independent of temperature and soil water content under non-flooded condition, although CO₂ evolution was highly correlated with these parameters. Aromatic carbon and hydrophobic acid contents in surface DOC were increased with wetter incubation treatments. In addition, positive linear correlations (r²=0.87) between CO₂-C mineralization rate and DOC concentration were observed in the surface soil, but negative linear correlations (r²=0.70) were observed in the subsurface soil. Results imply that mineralization of soil organic carbon by microbes prevailed in the subsurface soil. A conceptual model using a kinetic approach is proposed to describe the relationships between CO₂-C mineralization rate and DOC concentration in these soils.  相似文献   

Pharmacokinetics of intravenous tramadol in dogs          下载免费PDF全文

Chantal J McMillan  Alex Livingston  Chris R Clark  Patricia M Dowling  Susan M Taylor  Tanya Duke  Rolf Terlinden 《Canadian journal of veterinary research》2008,72(4):325-331

The purpose of this study was to determine the pharmacokinetics of tramadol and the active metabolite mono-O-desmethyltramadol (M1) in 6 healthy male mixed breed dogs following intravenous injection of tramadol at 3 different dose levels. Verification of the metabolism to the active metabolite M1, to which most of the analgesic activity of this agent is attributed to, was a primary goal. Quantification of the parent compound and the M1 metabolite was performed using gas chromatography. Pharmacodynamic evaluations were performed at the time of patient sampling and included assessment of sedation, and evaluation for depression of heart and respiratory rates. This study confirmed that while these dogs were able to produce the active M1 metabolite following intravenous administration of tramadol, the M1 concentrations were lower than previously reported in research beagles. Adverse effects were minimal, with mild dose-related sedation in all dogs and nausea in 1 dog. Analgesia was not documented with the method of assessment used in this study. Tramadol may be useful in canine patients, but additional studies in the canine population are required to more accurately determine the effective clinical use of the drug in dogs and quantification of M1 concentrations in a wider population of patients.  相似文献   

副猪嗜血杆菌感染诊断方法和最新基因分型方法的研究进展   总被引：1，自引：0，他引：1  

Alex Olvera  Joaquim Segales  李艳  刘静  吴移鼎 《国外畜牧学(猪与禽)》2008,28(5)

副猪嗜血杆菌可引起猪格拉塞病和其它许多疾病,对与该茵有关的疾病进行诊断通常依赖于临床症状、病理变化和细菌分离,但由于有无毒菌株(nonvirulent strain)的存在及其在健康仔猪上呼吸道上的早期定殖,使得对该菌的诊断变得较为复杂.而且,在同一猪场甚至是同一只猪体内可能存在多种不同的菌株,因此确定可导致临床发病的特定菌株显得尤为重要.最近,科研人员开发了一些针对副猪嗜血杆菌的基因分型方法,目的是确定该茵的基因型与其毒力强度之间的关系.由于缺乏副猪嗜血杆菌完整基因组序列及其致病因子(virulence factor)的知识,因此将副猪嗜血杆菌的基因型与其毒力联系起来极富挑战性.  相似文献   

Eisbruchschaden,speziell in der Oberförsterei Buchsweiler     

Bargmann 《European Journal of Forest Research》1906,28(4):198-206

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Effects of Cylindrospermopsin Producing Cyanobacterium and Its Crude Extracts on a Benthic Green Alga—Competition or Allelopathy?     

Viktória B-Béres  Gábor Vasas  Dalma Dobronoki  Sándor Gonda  Sándor Alex Nagy  István Bácsi 《Marine drugs》2015,13(11):6703-6722

Cylindrospermopsin (CYN) is a toxic secondary metabolite produced by filamentous cyanobacteria which could work as an allelopathic substance, although its ecological role in cyanobacterial-algal assemblages is mostly unclear. The competition between the CYN-producing cyanobacterium Chrysosporum (Aphanizomenon) ovalisporum, and the benthic green alga Chlorococcum sp. was investigated in mixed cultures, and the effects of CYN-containing cyanobacterial crude extract on Chlorococcum sp. were tested by treatments with crude extracts containing total cell debris, and with cell debris free crude extracts, modelling the collapse of a cyanobacterial water bloom. The growth inhibition of Chlorococcum sp. increased with the increasing ratio of the cyanobacterium in mixed cultures (inhibition ranged from 26% to 87% compared to control). Interestingly, inhibition of the cyanobacterium growth also occurred in mixed cultures, and it was more pronounced than it was expected. The inhibitory effects of cyanobacterial crude extracts on Chlorococcum cultures were concentration-dependent. The presence of C. ovalisporum in mixed cultures did not cause significant differences in nutrient content compared to Chlorococcum control culture, so the growth inhibition of the green alga could be linked to the presence of CYN and/or other bioactive compounds.  相似文献   

Genetic variability of pure <Emphasis Type="Italic">Pseudoplatystoma corruscans</Emphasis> and <Emphasis Type="Italic">Pseudoplatystoma reticulatum</Emphasis> individuals in the Paraná and Paraguay River basins     

Jussara Oliveira Vaini  Bruno do Amaral Crispim  Danielly Beraldo dos Santos Silva  Celso Benites  Marcia Regina Russo  Alexéia Barufatti Grisolia 《Fisheries Science》2016,82(4):605-611

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Community Changes and Growth in Small Cities: Resident Perceptions of Growth in Brandon,Manitoba, Canada          下载免费PDF全文

Doug Ramsey  Alex Michalos  Derrek Eberts 《Growth and change》2016,47(4):682-699

While research on rural depopulation and urbanization to large cities has dominated the literature for decades, small city growth has been largely ignored. Yet, small cities are important to the regional systems in which they are located, including serving as centres to their rural surround. This paper is concerned about growth and change in small cities. Using Brandon, Manitoba as an example, citizen perceptions of a range of specific aspects of city growth are analyzed. The study is based on a household postal survey conducted in May and June 2010 in which 2,500 randomly selected households in Brandon, Manitoba received questionnaires. The results are based on the 518 useable, completed questionnaires that were returned. Differences in perceptions of the pace of change in a range of aspects of development were found based on income, age, educational attainment, employment status, and home ownership. No differences were found based on gender. The paper concludes with comments about how city governments need to be aware of citizen perceptions when pursuing and managing development. The paper also illustrated the importance of citizen perceptions in understanding the pace and direction of change in small cities.  相似文献   

Attempts to determine the effects of forest cover on stream flow by direct hydrological measurements in Los Negros,Bolivia     

Valentin Le Tellier  Alex Carrasco  Nigel Asquith 《Forest Ecology and Management》2009

Underlying many payments for watershed services (PWS) schemes in tropical montane forest contexts is the assumption of a direct positive relationship between forest cover and dry season stream flow. We developed a low cost research program to assess the forest cover-stream flow relationship in the Los Negros watershed in eastern Bolivia. We asked three questions: (1) can watersheds that are similar enough to undertake paired catchment studies be identified using only simple parameters such as size, aspect and geographic proximity; (2) can a functioning locally based hydrological monitoring system be set up for less than $10 000 by training local farmers to collect hydrological data, and (3) can such data be used to improve the functioning of a PWS initiative? A land use map of the upper Los Negros valley was created from a 2005 Landsat image and a digital elevation model used to calculate physical and hydrological properties of 10 sub-watersheds. Farmers measured stream flow rates in these sub-watersheds from 2005 to 2008 and maintained 10 automatic rain gauges. We found no relationship between forest cover and stream flow. This may indicate that no such relationship exists, but could also reflect the short period of the study, the low quality of the data, and the fact that the sub-watersheds had relatively similar forest coverage (54–76%). We conclude that (1) watersheds can be identified as “similar-enough-for-analysis” using the criteria of size, aspect and proximity without undertaking further research, (2) a useful hydrological monitoring system can be developed for <$10,000 and (3) although our local farmers did not collect sufficiently high quality data to fully explore the forest/water relationship in Los Negros, with improvements in methodologies, low cost, locally based monitoring has the potential to be an important component of future PWS initiatives. We recommend that stream discharge should be calculated directly; only the most locally relevant hydrological criteria, rather than scientifically complete criteria, should be monitored; locally based monitoring must be institutionalized to reduce staff turnover and hydrological monitoring must be embedded within a context that makes it socially acceptable.  相似文献   

Spatial variation of fiber quality and associated loan rate in a dryland cotton field     

Yufeng Ge  J. Alex Thomasson  Ruixiu Sui  Cristine L. Morgan  Stephen W. Searcy  Calvin B. Parnell 《Precision Agriculture》2008,9(4):181-194

A field study was conducted in 2006 in a dryland cotton field in Texas, USA, to explore the spatial variation of cotton fiber quality and the loan rate associated with it. A total of 66 cotton samples were hand-harvested, and the fiber quality properties investigated included the High Volume Instrument measurements of micronaire, length, uniformity, strength, elongation, reflectance (Rd) and yellowness (+b). Conventional statistics showed a generally low level of variation in fiber quality with coefficients of variation <10%. Variogram analysis showed that all fiber quality properties were spatially correlated. Contour maps of individual fiber quality properties were produced from block kriged estimates. Fiber length, uniformity, strength and Rd were positively correlated, and all of these were negatively correlated with +b. The spatial distribution of most fiber quality properties was similar to that of soil apparent electrical conductivity, suggesting that water holding capacity could be a limiting factor for cotton fiber quality. Maps of individual fiber quality properties were combined with the United State Department of Agriculture—Commodity Credit Corporation Loan Schedule for Upland Cotton to create a loan rate map that is associated with fiber quality. A loan rate difference of 20 cents kg^–1 was observed within the field. This level of difference indicated that fiber quality at the field level can have a large impact on producers’ revenue. A site-specific management system encompassing both lint yields and fiber quality is strongly recommended for cotton production.  相似文献   

Soil condition classification using infrared spectroscopy: A proposition for assessment of soil condition along a tropical forest-cropland chronosequence     

Alex O. Awiti  Markus G. Walsh  Keith D. Shepherd  Jenesio Kinyamario 《Geoderma》2008,143(1-2):73-84

Soil fertility depletion in smallholder agricultural systems in sub-Saharan Africa presents a formidable challenge both for food production and environmental sustainability. A critical constraint to managing soils in sub-Saharan Africa is poor targeting of soil management interventions. This is partly due to lack of diagnostic tools for screening soil condition that would lead to a robust and repeatable spatially explicit case definition of poor soil condition. The objectives of this study were to: (i) evaluate the ability of near infrared spectroscopy to detect changes in soil properties across a forest-cropland chronosequence; and (ii) develop a heuristic scheme for the application of infrared spectroscopy as a tool for case definition and diagnostic screening of soil condition for agricultural and environmental management. Soil reflectance was measured for 582 topsoil samples collected from forest-cropland chronosequence age classes namely; forest, recently converted, RC (17 years) and historically converted, HC (ca.70 years). 130 randomly selected samples were used to calibrate soil properties to soil reflectance using partial least-squares regression (PLSR). 64 randomly selected samples were withheld for validation. A proportional odds logistic model was applied to chronosequence age classes and 10 principal components of spectral reflectance to determine three soil condition classes namely; “good”, “average” and “poor” for 194 samples. Discriminant analysis was applied to classify the remaining 388 “unknown” samples into soil condition classes using the 194 samples as a training set. Validation r² values were: total C, 0.91; total N, 0.90; effective cation exchange capacity (ECEC), 0.90; exchangeable Ca, 0.85; clay content, 0.77; silt content, 0.77 exchangeable Mg, 0.76; soil pH, 0.72; and K, 0.64. A spectral based definition of “good”, “average” and “poor” soil condition classes provided a basis for an explicitly quantitative case definition of poor or degraded soils. Estimates of probabilities of membership of a sample in a spectral soil condition class presents an approach for probabilistic risk-based assessments of soil condition over large spatial scales. The study concludes that reflectance spectroscopy is rapid and offers the possibility for major efficiency and cost saving, permitting spectral case definition to define poor or degraded soils, leading to better targeting of management interventions.  相似文献