| Biological soil crusts are widely developed in loess area in China and has a very important ecological effects. To understand the features of formation and distribution of biological soil crusts further, this paper did the research from the physical and chemical properties of biological soil crusts to environmental factors affecting the distribution and formation to the natural recovery and artificial cultivation to how to affect vegetation seed germination and emergence, with biological soil crust as the research object based on a large number of field investigations and laboratory experimentsBased on the field investigation in Wuqi county, Shaanxi Province in July 2008 and laboratory analysis to understand the physicochemical properties changes of biological soil crusts in the course of their development in hilly-gully regions of the loess plateau, soil mechanical composition, soil nutrients and chemical elements with different biological soil crusts coverage-the relevance between soil factors and biological soil crusts coverage, and the interrelation among soil factors during development of biological soil crusts were studied. With the development of biological soil crusts organic matter, total nitrogen, total potassium, available nitrogen, available phosphorus, available potassium increased, but pH value decreased. The biological soil crusts were mainly constituted by the fine sand (0.25-0.05mm) and coarse silt (0.05-0.01mm) soil particles. With the biological soil crusts coverage increased, the chemical elements content in soil including K, Na, Ca, Mg, Fe, Mn, Cu, Zn, Cr, Ni, Co also showed increase trend, in which Ca, Fe, K, Mg and Na content was higher. Soil organic matter, total nitrogen, total phosphorus, pH, fine sand, coarse silt, Ca, Mg, Na, and Fe content were closely related to the formation of biological soil crusts(P<0.01). In addition, during the process of biological soil crusts formation there were interrelations among soil factors. Especially coarse silt content and pH value that had significant interaction with other factors(P<0.01).Through the correlation analysis and path analysis of topography (slope, aspect, topography position), vegetation (vegetation cover, vegetation height, vegetation species number, litter cover) and interference factor with biological soil crusts cover, we found that the slope and interference factor were most closely related to biological soil crusts cover and their direct effect was the strongest. The indirect effect of the slope position, vegetation height, plant species number and litter coverage through other factors on the biological crust cover was large. As the slope increases, the biological crust cover tended to increase. The biological soil crusts cover of north slope was bigger than that of south slope. Biological soil crusts cover had reduced trends from mountain ridge from the gully to the top of slope. There was competition relationship between distribution of biological soil crusts and vegetation (including vegetation cover and height). The vegetation species number and litter had little effect on biological soil crusts. As interference level increases, biological crust cover continued small rapidly.In order to understand the effect of biological soil crusts(BSCs) on seed emergence and growth in loess region, we conducted field surveys and studied the impact of intact crusts, broken crusts and soil on the four seeds emergence including Pinus tabulaeformis, Caragana korshinskii, Hippophae rhamnoides and Pyrus betulifolia, based on the field emergence experiment from July to August in 2009 in Wuqi county, Shaanxi Province. The results revealed that with the BSCs cover and thickness increased the vegetation coverage reduced significantly (P<0.01) and vegetation types had a increasing trend(P> 0.05). Plant types and crust types (intact crusts, broken crusts and soil) affected seed emergence rate and emergence process(P<0.01), and the interaction between the two had little effect on seedling emergence (P>0.05), but had significant effect on the emergence process(P<0.01). The seed emergence rate of broken BSCs was higher than intact BSCs showed no significant difference with soil, and broken BSCs influenced seed emergence rate by the seed types. Broken BSCs could increased plant biomass and the shoot ratio of plants under soil is the maximum, but intact BSCs affected the plant biomass and shoot ratio depending on the types of seed.This study showed the biological soil crusts continued bigger as the increased formation time of the exposed slope that was excavated through field research on natural recovery of biological soil crusts. The recovery speed and moss ratio of biological soil crusts on north slope was bigger than that on south slope. After 2 years when the biological soil crusts formed on north slope, the biological soil crusts appeared and grew into the stable phase after 10 years. The biological soil crusts took large area after 20 years when the south slope formed. With the the artificial propagation of biological soil crusts that treated as inoculation method (discrete fragments, slurry), inoculation volume (200g,400g,600g,800g, 1000g), fertilization (with fertilizer, no fertilizer), This study found the interaction of inoculation volume and fertilization was more significant, in which the the recovery of biological crust was best under the condition of inoculation method (discrete fragments)×inoculation volume (1000g)×fertilization (with fertilizer). In addition, the growth of biological soil crusts was not controlled by water and heat, and the growth speed of which was the most fast in rainy season but slower than the vascular plants.
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