| Soil infiltration and runoff generation process are important research topics in the hilly Loess Plateau region. Biological soil crusts(biocrusts) were extensively developed on the surface of revegetated lands after the implementation of the “Grain for Green” Project and became the important influence factors on soil water infiltration and runoff process. The distribution pattern of vegetation and biocrusts patches were investigated in six successive rainfall zones ranging from 250 mm to 550 mm in the Loess Plateau region in the study. The effects of different type of biocrusts and plant species on soil infiltration were measured and the mechanism of infiltration differences was analyzed. Then, the effect of biocrusts and vegetation patches were implored by simulated rainfall experiment so as to clear the runoff source-sink relationship between biocrusts and vegetation patches. In addation, the effect of biocrusts types, plant species, biocrust and vegetation plaque area ratio, distribution patterns, and intensity of precipitation, slope gradient and length were also implored. The results were as follows.1) Biocrusts were developed in extensively in the revegetated lands in all of the rainfall zons investigated. The distribution pattern of vascular plants and biocrusts patches showed a mosaic pattern across the six rainfall gradients. Biocrusts were often distributed continuously within each site, while vascular plants often existed in patchys. Coverage of vascular plants and biocrusts has a significant negative correlation between the 250-550 mm rainfall zones. Total percentage cover of biocrusts of different the rainfall range investigated were significant varied, however, no significant difference was observed in the community composition of biocrust along this gradients.2) As respect to the influe nces on soil infiltratin, significant differences were found between biocrusts’ types as well as plants species. Generally, the soil under plants with tap roots exhibited higher stable infiltration rates than bare soil, while, the stable infiltration rates of soil under plants with fibrous roots did not showed significant difference compared with bare soil. O verall, infiltration potential of soils under varscular plants was higher than soils with biocrusts. Soil water content within the top 10 cm soil were siginificant influenced by the biocover after rain.3) A “source-sink” relationship of runoff between biolcrusts and vegetation patches was observed in the study. Runoff was increased for the present of biocrusts during a rainfall event, thus biocrusts worked as a "source" of runoff on the revegated slopes, while vegetation as "sinks", which slowing the runoff generation. Generally, the amount of runoff from the revegated slopes with biocrusts developed may increased along with the relative ratio between biocrusts and plant stem base. Biocrust played a positive role in the rainfall- runoff ecological processes, which can be regarded as the "source" landscape. However, the vegetation canopy interception rainfall and resulted in a reduced runoff amount, both the above and below ground parts of varscular plants played a negative role in the runoff processes, which can be considered as a "sink" landscape.4) Rain intensity significantly affected the source- sink relationship between biocrust- vegetation patches. In addition, the length of the slope was an impact factor during the process. The amount of runoff s howed increase trend whe n the length was bellow eight meters, however, the amount of runoff may be decreased when the length of the slope was longer than eight meters in the study. Vegetation patterns(random, striped, aggregation) and slope(16 °, 25 °) have no significant effect on biological crust-the vegetation runoff source- sink relationship, but the runoff volume exhibit aggregative pattern > random pattern > trend stripe pattern. |
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