Impacts of rising atmospheric carbon dioxide on model terrestrial ecosystems

In model terrestrial ecosystems maintained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations.

Long-term study of litter decomposition on a Pennine peat bog: which regression?

It is estimated that in the northern hemisphere one-third of the world pool of soil carbon is contained in peat resulting from an incomplete decomposition of plant remains. The time course for the decomposition of the predominant plant litters on a Pennine moorland in northern England is reported for a study extending over 23 years. Spatial variation of the weight remaining of decomposing litters increased with time. This experimental study gave an age for the upper layers of the bog and a curve for long-term decay based on direct observation rather than inferred from profile samples or from short-term observations. It showed that short-term observations can give misleading results in the long term, with a variety of litters with differing early decay rates ultimately making a similar contribution to accumulation. Spatial variation of the weight remaining of the decomposing litters increased with time, so that variation within micro-environments, or within apparantly uniform substrates, may contribute significantly to organic matter accumulation. An asymptotic curve best described the long-term course of decomposition leading to the accumulation of peat. The use of the model for the three litter types, Calluna vulgaris, Eriophorum vaginatum and Rubus chamaemorus, is described and the implication of the results for modelling of organic matter accumulation are then discussed.

Bactericidal effects of norfloxacin towards bacteria in urine.

Norfloxacin produced a reliably bactericidal effect at concentrations from 3 to 90 mg/l against urine pathogens suspended in human urine. These included Enterobacteriaceae, Pseudomonas aeruginosa, Streptococcus faecalis and Staphylococci. Resistant mutants of Staphylococcus aureus were isolated on two occasions (out of 33 experiments). At high concentrations (c. 90 mg/l) the activity was less but this was probably due to the need for a low pH to dissolve the antibiotic. The pH for optimum activity of norfloxacin in urine was 7.5 to 8.0. Human blood had little effect on the bactericidal activity. Compared to other antibiotics, the rate of killing of cultures in urine was second only to gentamicin.

In-vitro evaluation of miokamycin: bactericidal activity against streptococci.

Miokamycin is a diacetyl derivative of the macrolide antibiotic, midecamycin. In vitro, it has an unusual spectrum, inhibiting the growth of Gram-positive cocci and anaerobes, but few Haemophilus spp; enterobacteria are highly resistant. Most erythromycin-resistant Staphylococcus aureus were sensitive (MIC approximately 0.8 mg/l). Resistance to miokamycin in Staph. aureus and streptococci was difficult to select, unless the staphylococci were already resistant to erythromycin. Both miokamycin and erythromycin were bactericidal towards groups A,B,C and G streptococci. Clinical trials of the drug in pelvic, upper respiratory, skin and soft tissue and other staphylococcal infections may be worthwhile.

Double-blind study to compare the selection of antibiotic resistance by amoxycillin or cephradine in the commensal flora.

Elderly patients with acute urinary infections were treated in a double-blind study with either amoxycillin or cephradine. In 52 patients who had received amoxycillin for one week about a third of all intestinal Escherichia coli were highly resistant to amoxycillin, and many were resistant to tetracycline, trimethoprim, or chloramphenicol. Cephradine selected less resistance. At a week after completion of chemotherapy, cephradine-resistant E coli were replaced by sensitive cultures at a greater frequency than were amoxycillin-resistant E coli. Neither antibiotic altered the skin flora. Amoxycillin, but not cephradine, selected for Enterobacteriaceae in the saliva. The propensity of amoxycillin to select resistance in E coli will limit its usefulness in treating urinary infections.

Bactericidal effects of cefotetan and other antibiotics in human fluids.

Antibiotics were added at final concentrations of 0.5 to 10 mg/l to either human blood, serum, urine, bile or ascitic fluid inoculated with sensitive cultures. Bactericidal effects were monitored by estimation of viable counts over 24 h at 37 degrees C. Cefotetan was reliably bactericidal to bacteria suspended in human urine over a wide range of conditions. Gentamicin, cefotaxime, cefotetan and azthreonam were predominantly bactericidal against Enterobacteriaceae in serum and blood; gentamicin, cefotetan and cefotaxime were bactericidal in bile, and cefotetan bactericidal in ascitic fluid. The above antibiotics all also produced a bactericidal effect against Haemophilus influenzae in serum, and the macrolides erythromycin and rosaramicin destroyed haemophilus in serum more rapidly than did ampicillin or amoxycillin. In most of these fluids, destruction (reduction in viable counts by greater than 10-fold) of the inoculum occurred within 2 to 4 h for gentamicin and 4 to 6 h for similar concentrations of beta-lactam agents.