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611.
Desertification and global change 总被引:2,自引:0,他引:2
Arid and semiarid regions cover one third of the continental areas on Earth. These regions are very sensitive to a variety of physical, chemical and biological degradation processes collectively called desertification. Although interest in desertification has varied widely in time, there is a renewed concern about the evolution of dryland ecosystems because (1) a significant fraction of existing drylands already suffers from miscellaneous degradation processes, (2) increasing populations will inevitably result in further over-utilization of the remaining productive areas, (3) climatic changes expected from the greenhouse warming might result in drier continental interiors, and (4) some of the desertification processes themselves may amplify local or regional climatic changes. This paper reviews some of the many aspects of this issue in the context of the Global Change research program. 相似文献
612.
The effect of inoculation and the type of carrier material used on the biofiltration of methyl sulphides 总被引:2,自引:0,他引:2
E. Smet G. Chasaya H. Van Langenhove W. Verstraete 《Applied microbiology and biotechnology》1996,45(1-2):293-298
Low elimination capacities (less than 10 g m-3 day-1) were observed for the odorant dimethyl sulphide (Me2S) when either wood bark or compost was used as the carrier material in a laboratory-scale biofilter. Enrichment experiments
were set up by incubation of garden soil samples during 4 weeks with 100 ppm (v/v) headspace concentrations of both Me2S and dimethyl disulphide (Me2S2). After transfer to a mineral medium, Me2S- and Me2S2-degrading enrichment cultures were obtained for all five soil samples tested, both compounds being converted stoichiometrically
to sulphuric acid. Upon inoculation of the laboratory-scale biofilter with one of these enrichment cultures (±120 g cell dry
weight m-3 reactor), the elimination capacity for Me2S increased in a 3-week period to 35 g m-3 day-1 and 680 g m-3 day-1 when wood bark and compost were used as the respective carrier materials. Both inoculated biofilters were able to degrade
Me2S2, however the elimination capacities obtained for Me2S2 were lower (e.g. 24 g m-3 day-1 for the wood bark filter) compared to those for Me2S. For both inoculated biofilters, a gradual decrease of the elimination capacity for the methyl sulphides was observed as
a result of acidification of the carrier material, suggesting that pH regulation is necessary if long-term biofiltration experiments
are to be performed.
Received: 6 June 1995/Received revision: 10 August 1995/Accepted: 22 August 1995 相似文献
613.
Comamonas testosteroni colony phenotype influences exopolysaccharide production and coaggregation with yeast cells. 下载免费PDF全文
A Comamonas testosteroni strain was isolated from activated sludge on the basis of its ability to coaggregate with yeast cells. On agar plates the following two types of colonies were formed: colonies with a mucoid appearance and colonies with a nonmucoid appearance. On plates this strain alternated between the two forms, making sectored colonies. In liquid medium with constant agitation no such change was observed. In the absence of agitation and in contact with a glass surface a culture with predominantly nonmucoid-colony-forming cells very rapidly shifted to a culture dominated by mucoid-colony-forming cells. In liquid medium the reverse was observed under stress conditions imposed by hydrogen peroxide, sodium dodecyl sulfate, or starvation. Nonmucoid cells formed very rapidly settling flocs with yeast cells, while coaggregation of mucoid cells with yeast cells did not occur. These findings may be relevant to the behavior of activated sludge microbial communities. 相似文献
614.