[Development and succession of biological soil crusts and the changes of microbial biomasses].

Biological soil crusts (BSCs) play important ecological roles in vegetation and ecological restoration in desert regions, and different crust developmental and successional stages have different ecological functions. In this experiment, the BSCs in Shapotou region (at southeast edge of Tengger Desert) were investigated to study crust development and succession through field investigation, microscopic observation combined with quantitative analysis of microbial biomasses. The results showed that BSCs in this region generally developed and succeeded from algal crusts, lichen crusts to moss crusts. With the development and succession of BSCs, crust photosynthetic biomass gradually increased, while microalgal biomass showed a first increasing and then decreasing trend. Among the crust algae (cyanobacteia), Microcoleus vaginatus, as the first dominant species, occupied the most algal biomass and reached a maximum of 0.33 mm3 x g(-1) crusts in algal crusts; while Scytonema javanicum and Nostoc sp. have their maximal biomasses in the later lichen crusts. In addition, it was found that the heterotrophic microbial biomass began to increase in algal crusts, and then decreased in lichen crusts; followed by another increase and the increase achieved the maximum at last in moss crusts. Through the correlation analysis, it was found that bacterial biomass significantly positively correlated with crust organic carbon and Na+ content, while fungal biomass positively correlated with K+ and Na+ content (P < 0.05). In conclusion, this study investigated the developmental and successional patterns of BSCs in Shapotou region, and discussed the effects of crust development and succession on several microbial biomasses from the point of view of environmental adaptation and functional requirement, which may be helpful for us to understand crust development and succession, and provide theoretical and practical significances for crust maintenance and management in ecological restoration of desertification regions.

[Development and succession of artificial biological soil crusts and water holding characteristics of topsoil].

In order to understand the improving effects of cyanobacterial inoculation on water retention of topsoil in desert regions, this work focused on the development and succession of biological soil crusts and water holding characteristics of topsoil after cyanobacterial inoculation in Qubqi Desert. The results showed that after the artificial inoculation of desert cyanobacteria, algal crusts were quickly formed, and in some microenvironments direct succession of the algal crusts to moss crusts occurred after 2-3 years. With the development and succession of biological soil crusts, the topsoil biomass, polysaccharides content, crust thickness and porosity increased, while the soil bulk density decreased. At the same time, with crust development and succession, the topsoil texture became finer and the percents of fine soil particles including silt and clay contents increased, while the percents of coarse soil particles (sand content) decreased proportionately. In addition, it was found that with crust development and succession, the water holding capacity and water content of topsoil showed an increasing trend, namely: moss crust > algal crusts > shifting sand. The water content (or water holding capacity) in algal and moss crusts were 1.1-1.3 and 1.8-2.2 times of those in shifting sand, respectively. Correlation analysis showed that the water holding capacity and water content of topsoil were positively correlated with the crust biomass, polysaccharides content, thickness, bulk density, silt and clay content; while negatively correlated with the porosity and sand content. Furthermore, stepwise regression analysis showed that the main factor affecting water content was the clay content, while that affecting water holding capacity was the porosity.

[Response of the artificial cyanobacterial crusts to low temperature and light stress and the micro-structure changes under laboratory conditions].

Low temperature and light are noticeable environmental conditions commonly experienced by cyanobacterial crusts growing in desert areas. Here we reported the effects of low temperature and light on the morphology, physiological characteristics and ultrastructural changes of artificial cyanobacterial crust. Firstly artificial cyanobacterial crusts were formed by inoculating Microcoleus vaginatus Gom. and Scytonema javanicum (Kütz.) Born et Flah onto shifting sand in Petri dishes. Then, the artificial cyanobacterial crusts were selected as the experimental materials and subjected to the following treatments: 28 degrees C + 60 microE x (m2 x s)(-1) (control), 10 degrees C + 60 microE x (m2 x s)(-1), 2 degrees C +60 microE x (m2 x s)(-1) and 2 degrees C + dark. On the 0th, 5th and 12th days during the experimental period, biomass (expressed as Chl-a), photosynthetic activities (optimal quantum yield, Fv/Fm), exopolysaccharide (EPS), scytonemin, carotenoid and C-phycocyanin contents of the crusts in different treatments were determined. We also observed the ultrastructural changes of the cyanobacterial crusts in the control and 2 degrees C treatments by means of scan electron microscope (SEM). Moreover, the morphological properties such as crust color, crust thickness and crust dry weight etc. were also examined. The results indicated that the morphology of the treated crusts suffered unfavorable effect under light and low temperature stress, and Chl-a, Fv/Fm, EPS, scytonemin and carotenoid contents as well as C-phycocyanin content of the treated crusts were all significantly lower than those of the crusts under control conditions (P < 0.05). When the cyanobacterial crusts were treated for 12 days under 2 degrees C + 60 microE (m2 x s)(-1), Chl-a, Fv/Fm, EPS, scytonemin and carotenoid contents as well as C-phycocyanin content within the crusts decreased by 61.48%, 94.89%, 66.37%, 31.01%, 59.38%, and 65.91%, respectively. Obvious destruction in ultrastructure was observed in the cyanobacterial crust under cold stress, such as the presence of numerous honeycombs within the crusts and the sparse and loose appearance of the algal filaments, etc. The research verified that the acquired treatments had negative effects on the morphology, growth and microstructures of the cyanobacterial crusts, and the cooperation of low temperature and dark could provide effective protection for the morphological, physiological and microstructural features of the crust subjected to cold and light stress. The aim of this study was to primarily discuss the responses of cyanobacterial crusts to low temperature and light stress, and to offer a basic understanding of cyanobacterial crusts against extreme environments in fields, which may have certain academic significance for researches interested in cyanobactrial crusts.