| Recently, biological soil crusts (BSCs) play more important role in arid and semi-arid ecosystem in the Loess Area of North Shaanxi Province. Few researches reported that population characteristics of lichen and moss plant of BSCs in this area. Systematic study was less about the effect of BSCs on topsoil biological activities in different habitat. Through field survey, collection and authenticate of specimen, determination of soil biological activities and artificial cultivated BSCs, population characteristics of lichen and moss plant of BSCs and soil biological activities were studied in response to BSCs in different habitat condition.(1)25species of lichens were found in BSCs derived from Loess Area of North Shaanxi Province, which belong to14genera and10families. Dominant family and genus were evident which were Verrucariaceae and Endocarpon, respectively.24species of mosses were found in BSCs, which belong to13genera and6families. Dominant family and genus were Pottiaceae and Barbula, respectively. In grazing banned watershed, Shannon-Weiner diversity index and species richness of lichens and mosses on the shady slopes were greater than that on the sunny slopes. At the same slope aspect, Shannon-Weiner diversity index gradually ascended from higher to lower slope positions. Results indicated that Shannon-Weiner diversity and Pielou evenness index of lichens and mosses have spatial heterogeneity due to the effect of slope position and aspect.(2) The relationships between crust type and topsoil enzyme activity, crust type and microbial quantity, crust type and microbial biomass were different. The soil enzyme activity under different crusts type is the algae-lichen-moss crust> algae-moss crust, algae-lichen crust> physical crust. In crust layer, the quantity of bacteria under algae-lichen-moss crust and fungi under algae-lichen crust were the most, but the quantity of actinomyces under algae-lichen crust has more accumulation. In soil layer under crust, the number of bacteria and fungi under algae-lichen crust were the most, but actinomyces under algae-lichen-moss crust has more accumulation. Compared with physical crust, three biological soil crusts can significantly improve the soil microbial biomass carbon and nitrogen contents, the order of improvement was algae-lichen-moss crust> algae-moss crust> algae-lichen crust> physical crust. There was extremely significant positive correlation between developmental stage of biological crust and soil microbial biomass carbon and nitrogen content (P<0.01).(3) Effects of different site types on topsoil biological activities under BSCs were different. In shady slope, the soil enzyme activity of BSCs was significantly higher than that in sunny slope (P<0.05), and soil enzyme activity of BSCs in steep slope was higher than that in gentle slope, but the difference was not significant. In different site types, soil microbial quantity under BSCs was the lowest in sunny steep slope. The number of fungi under BSCs was highly significant difference (P<0.01). Soil microbial biomass nitrogen content of BSCs in shady slope was significantly higher than that in sunny slope (P<0.05), but no significant difference existed in slope factor. The soil microbial biomass carbon of crust layer have the same change with soil microbial biomass nitrogen content in different site type. In soil layer under BSCs, however, soil microbial biomass nitrogen content in shady steep slope was lower than other site type (P<0.05). In different site types, aspect factor could significantly affect topsoil microbial activities of BSCs, and the effect of slope factor on soil microbial activity was weaker than aspect factor.(4) In steep slope, the effect of forest and grass on soil microbial activities under BSCs was different. In sunny and shady slope, soil urease under BSCs has higher activity in enclosure grassland, while soil alkaline phosphatase activity under BSCs in enclosure grassland and Populus simonii forest were higher than Armeniaca sibirica forest and physical crust. Soil invertase activity under BSCs in three forest and grass vegetation were higher than physical crust. In shady slope, soil microbial quantities under BSCs in enclosure grassland were the most in all vegetation types. In sunny slope, the quantity of bacteria and actinomyces under BSCs was the most in Armeniaca sibirica forest and enclosure grassland, and fungi quantity under BSCs in forestland was more than enclosure grassland and physical crust. In shady and sunny slope, soil microbial biomass carbon content under BSCs was higher in enclosure grassland than forestlands and physical crust, and soil microbial biomass nitrogen content also has the same change in shady slope. In sunny slope, however, soil microbial biomass nitrogen content in the three forests vegetation types was higher than that in physical crust. Results indicated that soil microbial activities under BSCs gradually decreased with increasing soil depth. Therefore, BSCs could improve soil microbial activities in topsoil.(5) The results indicated that the coverage of artificial cultivated BSCs was more than65%after72days of cultivation. Moss crust coverage reached to40%after35days of cultivation. Compared with the control, soil organic matter and available nitrogen contents in moss crust with the horizontal treatments increased by100.87%and48.23%, respectively; and increased by67.56%and52.17%in sloping treatments, respectively. Available phosphorus content in cultivated BSCs was decreased. Soil pH was lower and cationic exchange capacity was higher in cultivated BSCs than in the control. Alkaline phosphatase, urease and invertase activities were increased in artificially cultivated BSCs. Alkaline phosphatase activity in all tratments of cultivated BSCs were significantly higher than that in the control. Quantities of soil bacteria, fungi and actinomycetes were increased in the formation process of cultivated BSCs. These results indicate that BSCs can be cultivated rapidly after short-term cultivation and improve the micro-environment of soil surface. These results will provide scientific basis for vegetation restoration and ecological reconstruction in the Loess Plateau, China. |
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