Influence Of Biological Crust On Soil Detachment Processes And Mechanisms In Red Soil Hilly Areas

Soil erosion is one of the“top ten threats”to soils worldwide and is a serious constraint to sustainable social and economic development.Although the soil erosion modulus of the red soil hilly area is smaller than that of the Loess Plateau,the soil layer is shallow and the relative soil erosion modulus is larger,so the problem of soil erosion is not optimistic.It is worth noting that the understorey provides shade while providing adequate light dispersion and also avoids competition for water and nutrients from vascular plants,so that the biological crust can grow widely in sparsely vegetated areas of the understorey,which provides a new idea for the prevention of soil erosion in the understorey of southern red loam hilly areas.However,research on biocrusts in the domestic and international has focused on arid and semi-arid areas,but less on wet areas,moreover,there is a lack of dynamic analysis of soil properties and soil erosion resistance response of the"biological crust-soil interface".The mechanism of biological crust affecting soil erosion resistance is still controversial.In view of this,this paper takes as its object of study the bryophyte crusts beneath economic forests and orchards,from the temporal scale,spatial scale and microscopic scale,through outdoor scouring tests and indoor analysis,to investigate the seasonal variation in the near-surface characteristics,subsurface soil properties and soil separation capacity of biocrusts in warp forests,to investigate the effect of biocrusts on soil water erosion and its mechanism,to analyse the contribution of the vertical structure of the biocrusts to the inhibition of soil detachment.The results of the study are as follows:(1)Biocrust near-surface characteristics were significantly affected by seasonal variation(P<0.05)and significantly correlated with monthly rainfall(P<0.05);However,for the crust layer and the subsoil properties,only the crust layer trend is more consistent with the biological crust development trend,and the subsoil properties show irregular changes;Soil nutrients,microbial activity and agglomerate stability at different soil depths show that the crust layer>0～5 cm>5～10 cm,and soil nutrients,microbial activity and agglomerate stability are significantly higher in the crust layer than in the lower layer.(2)The trend in soil separation capacity on the time scale is consistent with the trend in the near-surface properties of the biocrust,which generally show a trend of increasing,then decreasing,then increasing;Multiple non-linear regression showed that seasonal variation in soil detachment capacity under biocrust development could be modelled using water flow shear,biocrust cover,and soil cohesion(R~2=0.728,NSE=0.728,n=420),and that the model overestimated soil detachment capacity by 2.22%,overall,the model can better explain the seasonal variation in soil detachment capacity caused by the development of biological crusts under the red soil hilly area.(3)The effects and mechanisms of the ideal developmental state of the biological crust on soil properties and soil detachment capacity were investigated on a spatial scale instead of a temporal scale.Biocrust near-surface properties and soil properties were significantly influenced by biocrust development(P<0.05),with biocrust thickness,biomass,plant height,soil cohesion,clay content,water-stable agglomerates and average agglomerate weight diameter all increasing with increasing biocrust cover;Soil depth,biological crust cover and the interaction between the two significantly affected soil nutrient content(P<0.05),with biological crust development significantly enhancing soil nutrients,and the nutrient phenoconcentration effect of high cover biological crust soils being more significant;Biocrust cover had a significant effect on soil separability(P<0.05),with soil detachmnet capacity reduced by 26.7%to 93.0%under biocrust cover compared to bare ground;soil detachment capacity was predicted using water flow shear,soil cohesion,and biocrust cover(R~2=0.835,NSE=0.835,n=180);partial least squares structural equation modelling indicated that biological crust development,in addition to directly affecting rill erodibility on its own(ground cover,mycelium and pseudorrhizal entanglement),also indirectly affects rill erodibility by influencing the properties of the underlying soil,but the direct effect of its own influence is greater than the indirect effect.(4)The dominant role of the biological crust in inhibiting soil detachment will change as the biological crust develops,with cover protection replacing anchor fixation in the dominant role of inhibiting soil detachment;During this process,the ability of nutrient phenology to inhibit soil detachment gradually increased and soil stability showed an optimizing trend,but the contribution of nutrient phenology was still the lowest among the three effects,indicating that the main mechanism of biological crust inhibition of soil detachment was still dominated by its own structure,which is consistent with the conclusion of the partial least squares structural equation model;The rill erodibility shows regular variation on all three scales,while the critical shear shows irregular variation.The results of the study are of great significance to the analysis of the mechanism of enhancing soil erosion resistance by biological crusts in red soil hilly areas,and can provide theoretical reference for the control of soil erosion in the forest undergrowth in the region.