| Biological soil crusts widely distributed on the Loess Plateau since the “Grain forGreen” ecological restoration project implemented in the region, which significantlyimproved the soil physical and chemical properties, promote soil development, improve theerosion resistance and stability of soil. In this paper, biological soil crusts in their differentdeveloping stages in the hilly Loess Plateau region was studied in oreder to explore its effectson soil physical and chemical properties and on soil structure and the influence mechanism.The study will provide effective theoretical support for the ecological restoration andconstruction on the Loess Plateau. The main results are as follows:1Biological soil crusts were a layer structure which has a strong stability in horizontaldirection. After390shakings, the losses in thickness and mass of the moss dominated crustwere47.3%and40.1%of the cyanobacteria dominated crusts. Stability of moss dominatedcrusts was the highest when moss coverage was up to60%, with the loss in mass andthickness being28.6%and22.7%of the cyanobacteria dominated crust (no moss).2Biological soil crusts can increase water-stable aggregates content covered by crustsunder0-2cm soil layer, but did not significantly improve the soil water stable aggregatecontent in sublayers. MWD value of0-2cm layer in cropland soil was only0.21mm, and thehighest biomass of moss crust MWD value was2.25mm. In the early development stage,MWD of0-2cm layer were different with that of sublayer. While the biological crustdevelopment to the climax community, the MWD value of0-2cm,2-5cm,5-10cm these3layers in moss crust sample had no significant difference.3Microaggregate contents mainly in the0.05-0.25mm and0.02-0.05mm. The content of0.02-0.05mm microaggregate in0-2cm layer, cultivated land>80%moss crust>20%mosscrust> algae crust. The content of0.05-0.25mm microaggregate, algae crust>20%mosscrust>80%moss crust> cultivated land. Various types of biological crusts has nosignificant effect on the micro-aggregate content in sublayer.4biological soil crust can protect the aggregate in subleyer, the protective effect of mosscrust better than others. after the rain the content of0.05-0.25mm aggregates covered by algal crust and mixed crust decreased significantly, while the moss crust had no significantchange.5Biological crusts significantly improved soil polysaccharide content in biologicallayer, polysaccharide content of moss crusts was the highest, up to6.69mg/g, polysaccharidecontent of the cultivated land was the lowest, only1.10mg/g. Biological crusts have noobvious effect on the content of polysaccharide in the sublayer.6The plant content of moss crusts, mixed crust, algae crusts in sublayer before the rainyseason, was only39.59%,19.47%and18.50%respectively, but the plant content of mosscrusts, mixed, algae crusts in sublayer after the rainy season was significantly higher thanthat before the rainy season, reached78.96%,42.76%and31.48%. Plant content in sublayerwas effected by the rainy season, the plant content after rainy season was significantly higherthan that before the rainy season. In addition, the plant content of moss crusts wassignificantly higher than that of algal crusts, the plant of content algal crusts in rainy seasonwas only35.73%, while the moss crust reached66.29%.7Biological soil crusts mainly increased soil structure stability by increasing the contentof organic matter, total nitrogen content, polysaccharides and other soil physical andchemical content. Factors which have significant correlation with the stability of crust soilwere the organic content, total nitrogen content, soil aggregate content, the polysaccharidecontent and biological crusts biomass. Among them, there was a significantly positivecorrelation between organic matter and MWD value(P<0.01); polysaccharide, total nitrogencontent had significant positive correlation with MWD value; silt, clay, sand had nosignificant correlation with MWD value. |
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