Impact of Biological Soil Crust on Soil Physical Properties in the Hilly Loess Plateau Region,China

Biological soil crusts(biocrusts) are ubiquitous living surface covers in many arid and semi-arid regions.It has been demonstrated that the coverage of biocrusts was over 70% in the hilly Loess Plateau region of China and it played many important roles,such as exerting observably impact on soil properties and improving soil antierodibility.But the response of soil physical properties to the development of biocrusts has been unclear so far.The objective of the study was to determine the impact of development of biocrusts(i.e.with variable biomass) on soil physical properties in hilly Loess Plateau region.In this study,soil samples were collected after biocrusts and vegetation coverage survey,and the soil physical properties including soil bulk density,soil porosity,field water holding capacity,cohesion and hardness of biocrusts in different developmental stages were determined.The results showed: 1) Fine particles content increased due to the development of biocrusts.The content of coarse sand decreased by 86% while fine sand increased by 45% with biocrusts developing from cyanobacteria dominated to moss dominated(biomass of moss was 4.31±0.12 g/dm2).2) With the development of biocrusts,soil bulk density and hardness were reduced while field water holding capacity,soil porosity and cohesion were increased significantly.Along with the development of biocrusts,soil bulk density was dropped by 15%.Soil hardness of biocrusts in later development stage was reduced by 68% compared with the early stage.Field water holding capacity was increased to 57%,adding about 36% compared with the early stage,while soil porosity gone up to 58%,increasing by about 14%.Cohesion of biocrusts was 6 or 7 times as much as that of subsurface soil(0-2 cm).3) Impact of biocrusts on soil physical properties was closely related to biocrusts'biomass.When biomass of moss in biocrusts was to 2.91±0.12 g/dm2,soil physical properties changed no longer significantly.4) Soil physical properties not only in the layer of biocrusts,but also in the subsurface soil under the biocrusts were affected by the development of biocrusts.In conclusion,the results of our study suggested that soil physical properties were influenced by the development of biocrusts significantly.The study would likely provide scientific basis for the mechanism of soil antierodibility improvement by biocrusts.