Search

The optimum growth of soil crust-forming cyanobacterial species occurs between 21 and 30 °C. When the temperature decreases below -5 °C, the liquid water in the cyanobacterial cells may freeze. In the natural environment, the temperature gradually decreases from autumn to winter, and the diurnal temperatures fluctuate enormously. It was hypothesized that the physiology of cyanobacterial cells changes in later autumn to acclimatize the cells to the upcoming freezing temperatures. In the present study, an incubation experiment in growth chambers was designed to stimulate the responses of cyanobacterial cells to diurnal temperature variations before freezing in late autumn. The results showed that "light" cyanobacterial soil crusts are more tolerant to diurnal temperature fluctuations than "dark" cyanobacterial soil crusts. After the first diurnal temperature cycle between 24 and -4 °C, the malondialdehyde (MDA) contents increased and the photosynthetic activity decreased. The superoxide dismutase activity increased, more extracellular polysaccharides (EPS) were secreted and the ratios of the light-harvesting and light-screening pigments decreased. With increasing numbers of diurnal temperature cycles, the MDA contents and photosynthetic activity gradually returned to their initial levels. Our results suggest that there are at least three pathways by which crust-forming cyanobacteria acclimate to the diurnal temperature cycles in the late autumn in the Hopq Desert, Northwest China. These three pathways include increased secretion of EPS, regulation of the ratios of light-harvesting and light-screening pigments, and activation of the antioxidant system. The results also indicate that late autumn is a critical period for the protection and restoration of the cyanobacterial soil crusts in the Hopq Desert., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

For the purpose of elucidating the environmental characteristics of anion surfactants [linear alkylbenzene sulfonates (LAS)] in the water of Lake Dianchi, a sampling investigation in the field from October 2006 to July 2007 and a batch of biodegradation experiments in the laboratory were carried out. The results showed that concentrations of LAS ranged from 18.6 to 260.1 μg L(-1), and the average concentration was 52.6 μg L(-1) in Lake Dianchi. The highest concentrations of LAS were found in the Northwest region, and the distribution of LAS varied through seasons, with much lower concentrations in fall than in any other seasons. LAS can be primarily biodegraded by microorganisms in the lake water, and the percentage of degradation was >97% after 28 days. Biodegradation of LAS was well-fitted with the kinetic model presented in this paper, and the half-lives ranged from 3.2 to 16.3 days. Temperature, pH, and initial concentrations could affect the biodegradation of LAS, among which temperature was the major factor influencing on biodegradation of LAS in water of Lake Dianchi.