Synchronization of mammalian cells with tritiated thymidine

Short exposures of mammalian cells to tritiated thymidine of high specific activity destroys the proliferative capacity of mammalian cells. Since the killing is limited to cells that have synthesized DNA in the presence of the labeled compound, an exposure duration of less than one generation can yield a synchronized population.     

Factors affecting N immobilisation/mineralisation kinetics for cellulose-, glucose- and straw-amended sandy soils

The kinetics of N immobilisation/mineralisation for cellulose-, glucose- and straw-amended sandy soils were investigated in a series of laboratory incubations. Three Scottish soils expected to exhibit a range of biological activity were used: a loamy sand, intensively cropped horticultural soil subject to large inputs of inorganic fertilisers and pesticides (Balmalcolm - pH 7.2, organic matter 3.3%); a sandy loam soil highly enriched with organic manures and used for organic vegetable production (Strathmiglo - pH 7.1, organic matter 7.3%); and a loamy sand soil of low fertility in a zero-grazing, low intensity organic ley-arable rotation (Aldrochty pH 6.0, organic matter 5.0%). Incubations of soils with 1,000 mg cellulose-C kg^-1 soil at 8°C, showed peak N immobilisation of 71Lj, 92Lj and 65ᆣ mg N g^-1 added C for the Balmalcolm (after 34 days), Strathmiglo (after 34 days) and Aldrochty soils (after 63 days). The N remineralisation by the end of the incubation (>300 days) was 0, 50 and 22 mg N g^-1 cellulose-C in the Balmalcolm, Strathmiglo soil and Aldrochty soils, respectively. Only about 30% of the N immobilisation could be explained by soil microbial biomass N accumulation (much less than expected from model simulations). The C/N ratio of the extra microbial biomass was quite wide (19). Bacterial, protozoan and nematode biomass accounted for only 18%, 0.1% and 0.5% of the extra C immobilisation, respectively. These data suggest that fungal biomass growth and deposition of recalcitrant fungal metabolites are the main sinks for the N immobilised. With 1,000 mg glucose-C kg ^-1 added to the Balmalcolm soil, about 75 mg N g^-1 added C were immobilised after 6 days. Under less well aerated conditions at 15°C, immobilisation of only 10-20 mg N g^-1 added cellulose C took place in 2-4 weeks, but soluble organic C increased greatly. The N remineralised after 4-6 weeks.     

Development and environment in Peninsular Malaysia: By Robert S. Aiken,C. H. Leigh,T. R. Leinbach and M. R. Moss. McGraw-Hill,Singapore. 1982. xx + 310 pp,numerous figures,plates and tables. 24·5 × 17·5 cm. ISBN 0 07099 204 5. Price: US$29·95

The accomplishments of the Government of India/UNDP/FAO Project in the conservation of three species of crocodiles during the period 1975 to 1982 are reviewed. Sixteen crocodile rehabilitation centres and eleven crocodile sanctuaries have been established. A total of 879 gharials, 190 estuarine crocodiles and 493 mugger have been released. A viable breeding population of gharials now exists in the National Ghambal Sanctuary. A Crocodile Breeding and Management Training Institute was established by the Government of India in 1980 and has trained 48 managers of crocodile stations. Improvements are required in the management of crocodile sanctuaries and the evaluation of crocodile habitat. Releases of crocodiles in the wild require monitoring of survival and movements. There is a need for educating the public about crocodile conservation.     

The Rothamsted soil and crop nitrogen service on Viewdata 1985–1989

Abstract. During the four consecutive winters between 1984 and 1989 a computer simulation model was used to estimate the amounts of nitrogen in a cereal crop and available from soil to the crop after winter. The model does this by taking account of daily weather and by making simple assumptions about the starting conditions each autumn after the harvest of the previous crop. Some of the information which was given to farmers on viewdata systems is displayed, together with maps showing the average amounts of nitrogen in soil and crop in spring over 10 years in eastern England. This 10-year average is used as a baseline against which to judge the simulations in each of the four winters of our viewdata service.     

Strategic use of crutching and dicyclanil to protect unmulesed sheep against breech strike

Objective   To test strategies for the application of dicyclanil and mid-season crutching to maximise protection of unmulesed sheep against breech strike.
Procedure   Three hundred and eighty unmulesed Merino weaners were randomly allocated to four groups either left untreated or treated by different strategies with 50 g/L dicyclanil. Treatments included breech treatment alone and breech plus body treatment, with two application times, immediately after shearing and 6 weeks after crutching or shearing. To assess protection, larval implants with newly hatched Lucilia cuprina larvae were applied to 10 different sheep from each group at 3, 4, 5 and 6 months after crutching and shearing and assessed for the development of strike at 48 hours. The concentration of dicyclanil was measured in wool samples clipped from the breeches of the test sheep.
Results   All dicyclanil treatments gave significant reduction in strike in comparison to controls up until 4 months after crutching but protection in the sheep treated immediately after shearing had waned at 5 months. Treating at 6 weeks after crutching provided significant reduction ( P < 0.05) in strike for 6 months. Results for strike incidence immediately after shearing and concentration of dicyclanil in the breech wool also suggested improvements in protection by delaying treatment for 6 weeks.
Conclusion   In most environments it should be possible to protect unmulesed sheep against breech strike with a carefully planned integrated control program incorporating strategically timed crutching, shearing and dicyclanil application. Delaying treatment with dicyclanil to at least 6 weeks after shearing or crutching increased the protection provided in comparison to treatment immediately after shearing.     

Functional resilience of soil microbial communities depends on both soil structure and microbial community composition

The effects of soil structure and microbial community composition on microbial resistance and resilience to stress were found to be interrelated in a series of experiments. The initial ability of Pseudomonas fluorescens to decompose added plant residues immediately after a copper or heat stress (resistance) depended significantly on which of 26 sterile soils it was inoculated into. Subsequent studies showed that both the resistance and subsequent recovery in the ability of P. fluorescens to decompose added plant residues over 28 days after stress (resilience) varied significantly between a sandy and a clay-loam soil. Sterile, sandy and clay-loam soil was then inoculated with a complex microbial community extracted from either of the soils. The resulting microbial community structure depended on soil type rather than the source of inoculum, whilst the resistance and resilience of decomposition was similarly governed by the soil and not the inoculum source. Resilience of the clay-loam soil to heat stress did not depend on the water content of the soil at the time of stress, although the physical condition of the soil when decomposition was measured did affect the outcome. We propose that soil functional resilience is governed by the physico-chemical structure of the soil through its effect on microbial community composition and microbial physiology.