| Biological soil crust(biocrusts)extensively developed in the Hilly Loess Plateau region after the“Grain for Green” eco-project was implemented in the region,with an average coverage of 60%-70%.Biocrusts played an important role in the soil hydrological cycle,affecting the process of water infiltration.Disturbance was a common natural phenomenon,and biocrusts were very sensitive to the varieties of natural and human disturbance.In this paper,aimed to determination of different disturbance intensities on the biocrusts community composition,soil physical and chemical properties and soil infiltration,simulated rainfall trails,linear run-on method and infiltration test and natural rainfall monitoring test were used in the typical Hilly Loess Plateau,combined with indoor analysis.The influence of the disturbance on the biocrustal soil infiltration was revealed by the mathematical statistics analysis,which provided the scientific basis for the ecological restoration construction and the scientific management of the cultivated land in the Hilly Loess Plateau.The results are as follows:(1)Disturbance could significantly affect the coverage and composition of biocrusts.The degree of impact was related to the disturbance intensities.Disturbance significantly reduced the coverage of biocrusts,increased the coverage of the bare soil,which was related to the disturbance intensities.The disturbance significantly reduced the biomass of cyanobacteria and moss,which was related to the intensities of disturbance.The biomass of cyanobacteria and moss decreased linearly with the increase of disturbance intensities.In the biocrustal soil box,compared with the undisturbed treament,20%-50% disturbance decreased by 7.7%,15.0%,14.8% and 32.8%,respectively.The reduction of moss coverage was 5.2%,7.2%,11.7% and 8.3%.The increase of bare soil coverage was 8.7%,17.4%,30.9% and 35.8% respectively.In the field scale,the biocrusts coverage of 9%-30% disturbance decreased by 7.7%,14.2%,23.4%,18.5% and 5.7% than that of the background.The cyanobacteria coverage of undisturbed reduced by 1.6% that of background.And the cyanobacteria coverage of 9%-20% disturbance decreased respectively 2.5%,9.6%,13.7%,5.5% than the background.The cyanobacteria coverage at 30% disturbance was increased by 0.7% than that of the background.And the moss coverage of 9%-30% disturbance decreased respectively 13.9%,6.8%,5.5%,7.4%,12.1% and 5.6% than the background.Coverage of cyanobacteria and bare soil under 9% and 14% disturbance increased by 3.5% and 9.4%,respectively,compared with the background.The difference was not significant.The coverage of disturbed and bare soil coverage at 17% and 30% disturbance increased significantly by 12.1%,14.3% and 23.3%,respectively than that of the background..The cyanobacteria biomass at 9%-30% disturbance decreased by 8.1%,21.1,28.4 %,37.8% and 38.3%,respectively than that of the background.And the moss biomass decreased by 67.1%,55.1%,55.1%,65.7% and 92.7% respectively than that of the background.(2)Disturbance significantly affected the biocrustal soil physical and chemical properties,and the degree of influence was related to the disturbance intensities and soil depth.Disturbance reduced the content of soil organic matter in the biocrusts and increased the surface roughness of the biocrusts.Disturbance had no significant effect on the physical and chemical properties in 0-2 cm soil layer.The content of soil organic matter in the biocrustal soil was decreased by 5.5%,24.6%,3.6%,4.4% and 3.3%,respectively than that of background.The change of organic matter in the biocrustal layer at the treatment of 14% disturbance was significantly lower than that of the background.The change of organic matter of other treatments decreased than that undisturbed treatment,but the difference was not significant.After one year,the content of organic matter in 0-2cm soil layer decreased with the disturbance of different intensities,and the changes of different treatments were not significant.Compared with the background,the bulk density at 9%-30% disturbance was increased by 6.6%,6.2%,5.7%,8.3% and 8.7%,respectively.The porosity of biocrustal soil was lower than that background.Compared with the background,the porosity at 9%-30% disturbance was decreased by 4.2%,4.1%,3.8%,5.0% and 5.3% respectively.The changes of bulk density and porosity amoung different disturbance treatments were not significant.The roughness values of the 20%-50% interference treatment were significantly increased by 48%,63%,62%,91% and 46%,respectively than the undisturbed in the biocrustal soil box.In the field scale,the roughness values at 9% disturbance were increased by 5.7%,and there was an increasing trend compared with the undisturbed treatment.But it did not reach the significance level.The roughness values under 14%-30% disturbance were significantly higher than that of the undisturbed treatment,the increase rate was 21.9%,34.5%,31.3% and 36.0% respectively.The total content of aggregates in 0-2 cm soil layer at 9%-30% disturbance decreased by 33.3%,30.6%,27.8%,25.8% and 26.6% than that of the background.Compared with the undisturbed treatment,the changes of total content of aggregates in 0-2 cm soil layer were not significantly different amoung different disturbance treatments.The mean weight diameter of the aggregates were decreased by 72.4%,72.3%,62.2%,63.4% and 64.6%,respectively than the background.There were no significant difference in the changes of mean weight diameter of the aggregates among the different disturbance intensities.(3)Disturbance affected the infiltration of biocrustal soil,and the infiltration was increased first and then decreased with the disturbance intensity.The level of influence was related to the disturbance intensity and the determination method.Under the condition of linear run-on method,in the biocrustal soil box,the difference of the steady infiltration rate of 20%-40% disturbance was not significant than the undisturbed treatment.The stable infiltration rate at 50% disturbance(1.93 mm·min-1)was significantly increased by 56.5% than the undisturbed treatment.At the field sacle,the stable infiltration rate(0.72 mm·min-1)at 28% disturbance was not significantly different from that undisturbed treatment.Compared with the undisturbed treatment,the stable infiltration rate of 35%,43% and 57% disturbance significantly increased by 46.4%,61.9%,and 57.1% respectively.There was an increasing trend in the steady infiltration rate(0.97 mm·min-1)of the 48% disturbance than the undisturbed treatement,but the difference was not significant.Under the condition of simulated rainfall,the disturbance significantly increased the infiltration rate.Comapared with the undisturbed treatment,the steady infiltration rate at 20%,30%,40% disturbance increased by 7.5%,10.1%,3.8%,but did not reach a significant level.The steady infiltration rate(0.97 mm·min-1)at 50% disturbance significantly increased by 22.6% compared with the undistuebed treatment.The stable infiltration rate(0.60 mm·min-1)of the removal of the biocrusts was significantly lower than that of other treatments,decreasing by 23.4% compared with the undisturbed treatment.Under the condition of natural rainfall,compared with the undisturbed treatment,the water depth under 9%-30% disturbance were decreased 21.5%,17.0%,5.6%,3.3% and 24.4%,respectively,but did not reach the significant level.Under the condition of linear run-on method,the stable infiltration rate was reached the maximum at 46% and 56% disturbance,respectively in biocrustal soil box at the field scale.Under simulated rainfall conditions,the stable infiltration rate reached the maximum at 44% disturbance.Under simulated rainfall conditions,the water depth was the lowest at 27% disturbance.(4)Disturbance increased soil infiltration through breaking the integrity of the biocrusts,reducing cyanobacteria coverage,increasing the coverage of disturbed cyanobacteria and bare soil.The dominant factor affecting the stable infiltration rate in biocrustal soil was disturbance intensity.The influencing factors of water depth of biocrustal soil were mainly disturbance intensity,disturbed cyanobacteria coverage,and cyanobacteria coverage.The contribution rate of the three factors to the water depth was 53.4%,among which the contribution rate of disturbance intensity and disturbed cyanobacteria coverage were 33.9%,and the contribution rate of cyanobacteria coverage was 19.6%. |
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