祁连山东麓高寒草甸不同退化程度草地土壤种子库特征研究

通过野外调查和种子萌发法对东祁连山高寒草甸4种不同退化程度草地(未退化,ND;轻度退化,LD;中度退化,MD;重度退化,HD)土壤种子库进行了比较研究。结果表明:4种退化程度草地种子密度大小为:轻度退化草地>未退化草地>中度退化草地>重度退化草地;未退化草地共发现了6种植物,主要为十字花科(Cruciferae)和毛茛科(Ranunculaceae)植物;轻度退化草地共发现了9种植物,主要为禾本科(Gramineae)、菊科(Compositae)和豆科(Leguminosae)植物;中度退化草地共发现了5种植物,主要为车前科(Plantaginaceae)植物;重度退化草地共发现了5种植物,主要为禾本科(Gramineae)植物;对于土壤种子库的物种多样性,轻度退化草地最有利于维持和保护该地区物种多样性,未退化草地和轻度退化草地显著优于中度退化草地和重度退化草地;总体来看,4种退化程度草地种子库种子与地面植被物种相似性均较低。     

草地退化演替过程及诊断研究进展

随着人口的不断增加和现代工农业文明的冲击,草地生态系统出现不同程度的退化,导致草地生态系统组成、结构、过程和功能等方面发生量和质的变化;对草地退化的系统理解是进行草地恢复与重建的基础与前提。本文综述了草地退化的内涵、驱动力、退化过程与特点,以及草地生态系统退化程度诊断等一系列问题,绘制了描述草地退化程度的概念模型;建议从生态学角度研究草地退化程度诊断时选择相应的气候顶级系统或受干扰程度较轻的"自然生态系统";从草地经营学角度研究草地退化程度诊断时选择适度放牧草地作为参照系统。归纳了退化草地生态系统诊断的生物途径、生境途径和功能服务途径;分析了草地退化程度诊断的方法与可选择的指标体系,并对草地退化程度诊断及草地恢复中应注意的事项进行了讨论。     

不同利用程度高寒干旱草地碳储量的变化特征分析

本研究对处于青海湖北部不同退化梯度草地的土壤碳储量以及植被的根系生物碳储量变化进行了研究。调查草地样本包括7个样地和4个土层,样地依次分别为严重退化草场、重度退化草场、中度退化草场、轻度退化草场、正常草场、封育3年草场和人工草场,土层分别为0～10,10～20,20～30与30～40 cm 4个土层。结果表明,在不同退化梯度上,土壤碳储量随着退化程度的减轻依次增大,总体上各样地之间的变化趋势为,在5-7月为轻度退化草地＞无退化草地＞中度退化草地＞重度退化草地＞人工草地草地＞封育草地＞严重退化草地;在8-10月为无退化草地＞轻度退化草地＞中度退化草地＞重度退化草地＞封育草地＞人工草地＞严重退化草地,严重退化草地土壤碳储量最低,其次为封育草地;封育草地和人工草地的碳储量显著的低于轻度退化和无退化草地(P<0.05),但在封育草地和人工草地之间无显著差异(P>0.05)。在不同的土层,土壤碳储量从上至下依次降低,且各层之间表现出显著差异(P<0.05)。在不同的月份,各土层深度的土壤碳储量,总体上均表现为5-6月份降低,6-10月份呈递增的变化趋势,而且不同退化草地都表现出了较为一致的变化趋势。     

西部草地退化的原因分析与生态恢复措施探讨

通过分析西部草地退化的原因,提出了退化草地的生态恢复方略。研究表明:脆弱的生态环境是西部草地退化的自然内营力,人为干扰和不合理利用是西部草地退化的主要驱动力,气候变暖变干是加速西部草地退化的辅助外营力;草地改良是轻度退化草地生态恢复的主要途径,草地封育是中度退化草地生态恢复的主要措施,人工草地建植是重度和极度退化草地生态恢复的主要手段。     

新疆天山北坡荒漠草地退化现状及展望

草地退化是当今世界面临的极为严峻的生态问题之一,特别是新疆天山北坡地区的荒漠草原,由于其独特的地理环境所导致的荒漠草地退化越来越受到人们的关注。分析了新疆天山北坡荒漠草地退化的现状,在总结了国内外荒漠草地研究概况的基础上,重点综述了对新疆天山北坡地区荒漠草地退化的研究进展;在新疆天山北坡地区的荒漠草地退化研究,近年来主要集中在荒漠草地退化多样性演替、荒漠草地退化特征、荒漠草地退化遥感监测和重牧下抗牧策略等方面;通过以上综述,提出了荒漠草地退化中需要进一步深入研究的4个问题,包括荒漠草地生态系统退化机理、荒漠草地退化评价体系、荒漠草地退化监测体系和生态恢复研究,并对今后该领域的研究做出了进一步的展望和分析。     

内蒙古草地退化与治理对策

内蒙古是以牧为主,农牧林结合多种经营的一个自治区.广阔天然草地是发展畜牧业的物质基础.但是随着人类生产生活日益增长的物质需求,对草地采取掠夺经营,导致草地退化、沙化问题严重.本文阐述了草地退化的概念、特征及内蒙古草地退化现状,分析了草地退化发生的原因,提出了治理草地退化的对策.     

称多县清水河乡典型退化草地调查研究

对玉树州称多县清水河乡典型退化草地不同退化梯度高寒草甸的群落结构持征、土壤养分和退化成因等进行了调查研究。结果表明,4种不同退化梯度的草地中,植物的物种多样性、土壤养分和含水量等均随退化程度的加剧而降低;原生植被和轻度退化草地是受害轻微的退化草地生态系统;重度退化草地和极度（“黑土型”）退化草地是受害程度极大的退化草地生态系统。     

祁连山黑河上游不同退化草地有机碳和酶活性分布特征

为揭示草地退化过程中土壤有机碳和酶活性的分布特征及相关性,在祁连山黑河上游俄博岭区域的高山灌丛草甸土上,根据草地退化程度,划分了未退化草地、轻度退化草地、中度退化草地、重度退化草地,采用野外采样室内分析方法,研究了不同退化草地土壤有机碳和酶活性的分布特征。结果表明：4种退化草地0～60 cm土层有机碳的含量、密度、储量,以及土壤酶活性变化顺序为：未退化草地>轻度退化草地>中度退化草地>重度退化草地;4种退化草地（从轻到重）0～10 cm土层有机碳密度是50～60 cm土层有机碳密度的1.78倍、1.98倍、1.87倍和2.00倍,说明土壤有机碳密度在表层具有很强的表聚性;4种退化草地不同土层有机碳的含量、密度和储量,以及土壤酶活性均随着土壤剖面垂直深度的增加而递减;4种退化草地土壤有机碳含量与有机碳密度、土壤酶活性成显著正相关关系。     

草地退化相关概念辨析

草地退化是草地生态学和草地经营学中倍受关注的问题。在已有研究成果和笔者的研究体会的基础上总结了草地退化中的几组重要概念,包括生态退化与草场退化、植被退化与土壤退化、结构退化与功能退化、绝对退化与相对退化、参照系统与退化程度以及草地退化小尺度定位研究与大尺度空间格局研究,对其进行辨析,同时指出这些概念的划分在草地退化理论与实践研究中的重要意义。     

退化草地土壤理化性质的研究简述

草地退化是整个草地生态系统的退化,土壤退化是草地退化的具体体现,是比植被退化更严重的退化,土壤严重退化后整个草地生态系统的功能会遗失殆尽。本文在阐述退化草地土壤理化性质相关概念的基础上,重点综述了退化草地土壤物理、化学性质方面的研究,提出退化草地理化性质方面存在的问题。认为在改良退化草地时,应考虑土壤退化程度,导致退化的主导因子及土壤性状等因素,并且对研究退化草地土壤的理化性质需长期持续研究。     

Phase I evaluation of CCNU (lomustine) in tumor-bearing cats

1-(2-Chloroethyl)3-cyclohexyl-1-nitrosourea (CCNU) is an alkylating agent in the nitrosourea subclass. A prospective evaluation of CCNU was done to determine the maximally tolerated dosage of CCNU in tumor-bearing cats. Response data were obtained when available. Twenty-five cats were treated with CCNU at a dosage of 50-60 mg/m3 body surface area. Complete hematologic data were available for 13 cats. Neutropenia was the acute dose-limiting toxicity. The median neutrophil count at the nadir was 1,000 cells/microL (mean, 2,433 cells/microL; range, 0-9,694 cells/microL). The time of neutrophil nadir was variable, occurring 7-28 days after treatment, and counts sometimes did not return to normal for up to 14 days after the nadir. Based on these findings, a 6-week dosing interval and weekly hematologic monitoring after the 1st treatment with CCNU are recommended. The nadir of the platelet count may occur 14-21 days after treatment. The median platelet count at the nadir was 43,500 cells/microL. No gastrointestinal, renal, or hepatic toxicities were observed after a single CCNU treatment, and additional studies to evaluate the potential for cumulative toxicity should be performed. Five cats with lymphoma and 1 cat with mast cell tumor had measurable responses to CCNU. Phase II studies to evaluate antitumor activity should be completed with a dosing regimen of 50-60 mg/m3 every 6 weeks.     

Production and characterization of rabbit anti-idiotypic antibodies directed against a murine monoclonal anti-B. abortus antibody

The protective anti-B. abortus monoclonal antibody ISS/32 (Ab1) was used as an immunogen to induce anti-idiotypic antibodies (Ab2) in rabbits. The purpose was to produce and characterize anti-idiotypic antibodies that share conformational similarity with the corresponding bacterial epitope recognized by Ab1. The rabbit anti-IdAb so induced was isolated and affinity-purified. Its specificity for the paratope of Ab1 was determined by evaluating its ability to compete withB. abortus for binding to Ab1 in a competitive ELISA assay. The anti-idiotypic ISS/32 antibodies were able to compete withB. abortus for binding to Ab1 in a dose-dependent manner. Hence, the data indicated that the rabbit anti-Id ISS/32 antibodies reacted with or near the antigen-binding site of Ab1.Abbreviations Ab antibody - anti-Id anti-idiotypic - ELISA enzyme linked immunosorbent assay - IgG immunoglobulin - i.p. intraperitoneal - mAb monoclonal antibody - PBS phosphate-buffered saline - s.c. subcutaneously - TD PBS + 0.05% Tween 20% + 1% yeast extract     

Investigations of Outbreaks of Contagious Caprine Pleuropneumonia in Eritrea

Mycoplasmas were isolated from freeze-dried lung samples from goats from the western lowlands of Eritrea suspected of being affected by contagious caprine pleuropneumonia. The goats belonged to two herds in which mortality and morbidity rates were high. Mycoplasma capricolum subsp. capripneumoniae was identified in most samples by the polymerase chain reaction and by conventional serological tests. The latex agglutination test detected more positive serum samples in both herds than did the complement fixation test. Following cloning, the isolates of M. capricolum subsp. capripneumoniae were analysed biochemically and shown to be metabolically similar. They oxidized glucose, N-acetylglucosamine, pyruvate and L-lactate with high affinity and mannose, glucosamine and 2-oxobutyrate with low affinity; they were unable to utilize maltose, trehalose, fructose or ethanol. Major improvements were seen in the growth yield of the Eritrean strains with the addition of pyruvate to the medium. Thus, it may be that organic acids are important energy sources for these strains and may be used in addition to or in place of glucose. In contrast to most other strains of the M. mycoides cluster, the Eritrean strains produced large amounts of hydrogen peroxide during the oxidation of NADH by lysed cells. This characteristic had previously been reported for strain M. F38, the type strain of M. capricolum subsp. capripneumoniae, although strain F38 did not metabolize sugars. Hydrogen peroxide has long been considered a pathogenicity factor in mycoplasma infections. This is the first isolation of M. capricolum subsp. capripneumoniae from Eritrea.     

The Epidemiology of Gastrointestinal Nematodes of Dairy Cattle in Central Kenya

The epidemiology of H. placei and of other gastrointestinal nematodes in yearling dairy cattle was examined on two farms in Kiambu District, central Kenya during each of 13 one-month periods from April 1993 to April 1994. On each farm, 32 newly weaned dairy calves were given a single dose of albendazole and then placed on experimental pastures. Twelve of the animals were designated for bi-monthly slaughter (n = 2) and analysis of worm population characteristics and 20 were designated for blood and faecal collection and for weighing. Two parasite-free tracer calves were grazed alongside the weaner calves each month throughout the study period and were also slaughtered for analysis of worm populations. Faecal egg counts, haematological and serum pepsinogen determinations, herbage larval counts, and animal live weight changes were recorded monthly. The study revealed that Haemonchus placei, Trichostrongylus axei, Cooperia spp. and Oesophagostomum radiatum were responsible for parasitic gastroenteritis and that H. placei was the predominant nematode present in the young cattle on both farms. Faecal egg counts from resident cattle and necropsy worm counts revealed that pasture larval levels were directly related to the amount of rainfall. The total worm burdens in the animals were highest during the rainy season (March–June and October–December) and lowest during the dry seasons (July–September and January–February). The very low recovery of immature larvae of H. placei from the tracer calves indicated that arrested development is not a feature of the life cycle of this parasite in central Kenya. The maintenance of the parasite population depended on continuous cycling of infection between the host and the pasture. The agroclimatic conditions of the study area were such that, in general, favourable weather conditions for the development and survival of the free-living stages of gastrointestinal nematodes existed all year round.     

Antibody responses to Toxoplasma gondii antigens in aqueous and cerebrospinal fluids of cats infected with T. gondii and FIV.

Antibodies to antigens of Toxoplasma gondii were measured in the aqueous and cerebrospinal fluid (CSF) of 16 specific-pathogen free kittens experimentally infected with feline immunodeficiency virus (FIV), T. gondii, or both pathogens. The results indicated that all cats infected with T. gondii had antibody responses to antigens of T. gondii in both aqueous fluids and CSF. Co-infection with FIV did not affect antibody levels. Aqueous fluids from eyes of cats with toxoplasmic retinochoroiditis did not necessarily have higher antibody levels than those from eyes without lesions. Antibodies to T. gondii were also detected in the CSF of two cats from whose brains no parasites were isolated by in vivo mouse inoculation. Total IgG did not increase significantly in the aqueous fluids and CSF of cats infected with T. gondii whether or not they were also infected with FIV.     

Bovine Mastitis due to Prototheca zopfii: Clinical,Epidemiological and Pathological Aspects in a Brazilian Dairy Herd

The clinical, epidemiological and pathological aspects of protothecal mastitis in a Brazilian dairy herd are described. Prototheca zopfii infection was diagnosed in 11 of 121 milking cows. Clinical mastitis refractory to usual therapy was observed in 7 cows. Several environmental conditions conducive to the growth of Prototheca spp., such as wetness, muddiness and the presence of organic material, were present in the dairy. Improper milking practices and insanitary infusion of the intramammary antibiotics were also observed. Six cows with protothecal mastitis were slaughtered and the affected quarters of each cow were examined by histology and immunohistochemical staining for bovine keratin and P. zopfii. The histological lesions were characterized by interstitial infiltrates of macrophages, plasma cells and lymphocytes; algae were seen in the alveolar lumen and interstitium. The lack of a positive reaction with an antiserum against bovine keratin in the mammary alveolar epithelial layer in some affected areas suggests destruction of milk-producing tissues, which may be related to the low milk production observed. The algal organisms stained positively with a polyclonal antibody against P. zopfii.     

Evaluation of biohydrogenation rate of canola vs. soya bean seeds as unsaturated fatty acids sources for ruminants in situ

An experiment was conducted to study disappearance of C14 to C18 fatty acids, lag times and biohydrogenation (BH) rates of C18 fatty acids of ground soya bean and canola seeds in situ. Three ruminally fistulated Dallagh sheep were used to determine ruminal BH of unsaturated fatty acids (UFAs). Differences in the disappearance of fatty acids through the bags and lag times were observed between the oilseeds. We saw that the longer the incubation time of the oilseeds in the rumen, the lower the content of C18:2 and C18:3. Significantly higher lag times for both C18:2 and C18:3 were observed in ground canola compared to ground soya bean. BH rates of C18:2 and C18:3 fatty acids in soya bean were three times higher than those of canola. These results suggest that the fatty acid profile of fat source can affect the BH of UFAs by rumen micro‐organisms. So that UFAs of canola had higher ability to escape from ruminal BH. It seems that fatty acid profile of ruminant products is more affected by canola seed compared to soya bean seed.     

Fungi onNarthecium ossifragum leaves and their possible involvement in alveld disease of Norwegian lambs

Spores ofPithomyces chartarum (Berk. & Curt.) M.B. Ellis were only rarely seen on leaves ofNarthecium ossifragum (L.) Hudson collected in summer from five areas in western Norway in which alveld, a photosensitization disease of lambs, is endemic.Cladosporium magnusianum (Jaap) M.B. Ellis was found on all 118 leaf samples collected in the summers of 1990 and 1991. The hypothesis thatP. chartarum contributes to the aetiology of alveld could not be supported, but it is possible thatC. magnusianum may have a role in the causation of the disease.     

Sensitivity of Certain Porcine and Bovine Mycoplasmas to Antimicrobial Agents in a Liquid Medium Test Compared to a Disc Assay

The sensitivity of some porcine and bovine mycoplasmas to potent antimicrobial agents was examined. Minimal inhibitory concentration (MIC) values were estimated for M. hyosynoviae, M. hyopneumoniae, M. dispar and M. bovis against enrofloxacin, lincomycin, tetracycline, tiamulin and tylosin, in a liquid medium test and in a disc assay. All 6 examined strains of each species and the respective type strains were significantly inhibited. The greatest sensitivity was noted for tiamulin against strains of M. hyosynoviae with a final MIC₅₀ broth value of 0.025 µg ml⁻¹ and disc value of 0.03 µg per disc. Enrofloxacin was found very potent against M. hyopneumoniae with a final MIC₅₀ of 0.025 µg ml⁻¹ and 0.1 µg per disc, and for M. dispar with 0.05 µg ml⁻¹ and 0.03 µg per disc.Most disc assay estimates in ug per disc were similar to or moderately greater than corresponding final broth figures in µg ml⁻¹. It may be possible to convert observed disc assay values into representative final broth MIC values for use in the clinic.