[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.