Diurnal and Seasonal Patterns in Ecosystem CO2 Fluxes and Their Controls in a Temperate Grassland

There is considerable interest in understanding processes of carbon dioxide (CO₂) uptake and release in grasslands and the factors that control them. Many studies have investigated how CO₂ fluxes vary over time (monthly, seasonally, annually). However, with the exception of net ecosystem CO₂ exchange (NEE) and ecosystem respiration (R_eco), little information is available on diurnal flux patterns, despite their importance in determining total ecosystem CO₂ gains and losses. To better understand these variations, we measured CO₂ fluxes (NEE, R_eco, soil respiration [R_soil], canopy respiration [R_canopy], plant assimilation [assimilation]) with a climate-controlled closed-chamber system over 24 h once a month from May to September during the 2005 growing season in a mesic grassland in Yellowstone National Park. We also assessed how environmental factors (photosynthetic active radiation [PAR], air temperature, soil temperature, soil moisture) were associated with these diurnal and seasonal flux patterns to identify the main drivers of the fluctuations in CO₂. Measurements were conducted simultaneously on two plots: one irrigated, the other unirrigated. Absolute values of all fluxes were greatest in midsummer (June–July), and lowest in spring and fall (May, September) at both plots. Variation in soil moisture as a result of irrigation did not lead to pronounced differences in seasonal CO₂ fluxes and did not influence the diurnal patterns of CO₂ uptake and release. Instead, the diurnal and seasonal variations of our ecosystem fluxes were related to PAR and temperature (air/soil) and soil moisture and temperature (air/soil), respectively, at both plots. Thus, continued anthropogenic increases in greenhouse gas emissions that are expected to change the intensity of radiation, temperature, and precipitation may strongly affect the diurnal and seasonal patterns in CO₂ uptake and release. Such chamber-based information combined with the measurement of environmental variables could be important for modeling CO₂ budgets when no continuous measurements are available or affordable.     

提高繁殖猪群效率纵横谈

繁殖猪群的目标是不断地以低成本生产计划数量的优质断奶仔猪。图 1显示了影响断奶仔猪产量的因素。断奶仔猪产量是繁殖群母猪存栏数 (能力 )与每头母猪年产断奶仔猪数 (效率 )的乘积。确定繁殖猪群的适当大小而使其适合于养猪设施的容量 ,同时确定后备母猪群的适当大小而使其适合于每周的配种计划 ,是为实现断奶仔猪产量计划和充分利用产仔栏所必需的。一般来说 ,是否适合于配种计划和分娩率 ,是影响每头存栏母猪年产断奶仔猪数量的最重要的因素(表 1 )。图 1　影响断奶仔猪产量的各种因素之间的相互关系　表 1　每周断奶仔猪产量影响因素…     

泌乳母猪的饲喂:科学和实践的结合

在星际旅行的时代 ,我们怎么能还在争辩怎样饲喂泌乳母猪的问题呢 ?如果我们能够破解动物的遗传编码 ,我们为什么不能理解采食量和泌乳母猪性能之间的相互关系呢 ?但是 ,也许我们确实理解了这些关系 ,不过我们不能将科学转化为良好的猪场实践。也许我们过分地试图将一般原则或指南应用于非常具有个性的具体场合之中 ,无论这些具体场合是指不同的猪种、不同的猪场或者不同的个体。每一头泌乳母猪都是独特的 ,将一般原则应用于独特的动物 ,一般来说结果都是不太令人满意的。但是 ,随着猪场规模的扩大 ,可能就越来越难以将每一头母猪都进行个别…     

Trends in antimicrobial susceptibility in relation to antimicrobial usage and presence of resistance genes in Staphylococcus hyicus isolated from exudative epidermitis in pigs

From 1996 to 2001 a total of 467 Staphylococcus hyicus isolates from exudative epidermitis (EE) in pigs in Denmark were examined for susceptibility to 13 different antimicrobial agents. The presence of selected genes encoding macrolide (erm(A), erm(B) and erm(C)), penicillin (blaZ), streptogramin (vat, vga, vga(B), vat(B), vat(D) and vat(E)), streptomycin (aadE) and tetracycline resistance (tet(K), tet(L), tet(M) and tet(O)) were determined in selected isolates.The occurrence of erythromycin resistance increased from 33% in 1996 to a maximum of 62% in 1997 and decreased to 26% in 2001. Resistance to sulphametazole increased from 17% in 1996 to 30% in 1998 but has since decreased to 4% in 2001. Resistance to trimethoprim increased to 51% in 1997 and decreased to 21% in 2001. Resistance to tetracycline (21-31%) remained relatively constant during 1996-2000, but increased to 47% in 2001. Resistance to penicillin (54-75%) streptomycin (33-53%) and tetracycline (21-47%) remained relatively constant over the time investigated.All 48 penicillin resistant isolates examined contained the blaZ gene and 40 (85%) of the streptomycin resistant isolates the aadE gene. It was not possible to detect any streptogramin resistance gene in four streptogramin resistant isolates. Of the 55 erythromycin resistant isolates examined, five contained erm(A), 13 erm(B), 35 erm(C) and two both erm(A) and erm(C). The presence of erm(B) was confirmed by hybridization to plasmid profiles in all 13 PCR-positive isolates. Of 52 tetracycline resistant isolates examined, two contained tet(L), 38 tet(K) and 12 both tet(K) and tet(L).     

Prospects for a novel vaccine against tuberculosis

The development of a new and improved vaccine against tuberculosis has in the last 10 years been accelerated tremendously from the completed Mycobacterium tuberculosis genome and the progress in molecular biology. This has resulted in the identification of a large number of antigens with potential in tuberculosis vaccines. The next phase of this work has now started--putting the most relevant molecules back together as fusion molecules and cocktails. This requires carefully monitoring of aspects as immunodominance, recognition in different populations as well as the influence of different adjuvants and delivery systems. The most advanced of these vaccines such as the fusion between ESAT6 and Ag85B have been evaluated in a range of animal models including non-human primates and are now entering into clinical trials. For these vaccines to be successfully implemented in future vaccination programmes it is necessary to understand the immunological background for the failure of BCG and optimize the vaccines for their ability to boost the immuno-response primed by BCG.     

Beef authentication and retrospective dietary verification using stable isotope ratio analysis of bovine muscle and tail hair

Stable isotope ratio analysis (SIRA) was used as an analytical tool to verify the preslaughter diet of beef cattle. Muscle and tail hair samples were collected from animals fed either pasture (P), a barley-based concentrate (C), silage followed by pasture (SiP), or silage followed by pasture with concentrate (SiPC) for 1 year (n = 25 animals per treatment). The (13)C/(12)C, (15)N/(14)N, (2)H/(1)H, and (34)S/(32)S isotope ratios in muscle clearly reflected those of the diets consumed by the animals. By applying a stepwise canonical discriminant analysis, a good discrimination of bovine meat according to dietary regimen was obtained. On the basis of the classification success rate, the (13)C/(12)C and (34)S/(32)S ratios in muscle were the best indicators for authentication of beef from animals consuming the different diets. Analysis of (13)C/(12)C and (15)N/(14)N in tail hair sections provided an archival record of changes to the diet of the cattle for periods of over 1 year preslaughter.     

Dissolved and colloidal phosphorus fluxes in forest ecosystems—an almost blind spot in ecosystem research

Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L^?1, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m^?2 a^?1, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.