Effect of crevice density on biological soil crust development on rock cut slope in mountainous regions, Sichuan, China

Background The rock cut slope（RCS） could cause damage to regional ecological functions and landscapes and requires recovery. Biological soil crusts（BSCs） are pioneer and dominant colonizers during the initial recovery stage. To accelerate the natural recovery of RCS, the development process and influencing agents of BSC should be revealed.Thus, the area index of crevices（IR）, BSC coverage（COV） and biomass（BM）, soil weight（SW）, and major soil nutrients [organic carbon（OC）, total nitrogen（TN） and total phosphorus（TP）] content, collected from 164 quadrats on 13 RCSs in the mountainous area of west Sichuan Province, China, were measured, to explore the effect of crevice of RCS on BSC development.Results Soil OC, TN and TP on RCSs ranged from 18.61 to 123.03 g kg-1, 0.96 to 6.02 g kg-1 and 0.52 to 2.46 g kg-1,respectively, and were approximately to or higher than those on natural slopes. The OC, TN and TP contents in soils elevated unsystematically with recovery time of RCSs. BSCs on RCS distributed along crevices generally and firstly.During the first 13 years of natural recovery, COV, BM and SW ranged from 6.5 to 28.2%, 14.43 to 67.25 g m-2, and 127.69 to 1277.74 g m-2, respectively. COV, BM and SW increased linearly with IR on RCSs. The positive correlation between COV and BM and IR was insignificantly impacted by bedrock, slope aspect and altitude within the recovery time less than 13 years. COV and BM on RCSs increased significantly when the recovery time is more than 27 years.Conclusions Crevice on RCSs could be a major environmental factor which is conducive to BSC development and soil accumulation through creating a space for water and soil particle. Furthermore, with the increase of recovery time of RCSs, BSCs may grow and reach a stable state with the promotion of soil nutrients, plant growth and microbial activity. These results provide a development process of BSC that from inside to outside the crevices on RCSs. In the areas with stable rock strata and a low risk of geological disasters, purposeful improvement in crevice density on RCS may effectively accelerate BSC development.