The impacts of soil properties and heavy metals on soil microbial communities in the artificial soils on railway rock-cut slopes

PurposeConstructions of roadways have created many rock-cut slopes, and artificial soils have been sprayed onto the rock-cut slopes to promote re-vegetation. The aims of the study were to (1) understand the physicochemical properties, heavy metal enrichment and microbial community conditions of the artificial soil on the rock-cut slopes re-vegetated for different years and (2) analyze the associations between environmental factors and microbial communities, identify main environmental factors and provide suggestions to promote slope ecosystem restoration.Materials and methodsNine rock-cut slopes located alongside railways constructed in different years (1996, 2003, 2007) were selected. Two natural slopes far away from the railways were selected as controls. At each rock slopes, five sampling transects with 1, 5, 15, 20, and 50 m from the track were created. At each transect, topsoil collected from 15 to 20 points along the transect comprised a soil sample. At the natural control slope, topsoil from more than 20 points scattered across the natural slope were collected and mixed together to obtain one soil sample. Total 47 soil samples were obtained. Soil physicochemical properties, microbial communities, accumulation of heavy metals and their relationships were investigated.Results and discussionsThe contents of clay and SOC, soil stability and erosion resistance ability increased with increasing re-vegetation time. However, there is a big gap that exists with natural slopes. The artificial soils were mainly polluted by Cd and Pb and tended to accumulate with increasing railway operation time. The dominant bacterial species of the study sites were similar but differed in abundance. Proteobacteria, Gemmatimonadetes, Bacteroidetes, and Actinobacteria at the phylum level and Sphingomonas, Haliangium, Bryobacter, and Gemmatimonas at the genus level dominated the soil microbial communities. The redundancy analysis results indicated that HCl-extractable Fe, AK and SOC were the most important factors affecting the microbial communities of the rock-cut slopes, and HCl-extractable Cd, HCl-extractable Cr, Cu and Cd also had some influence.ConclusionsMonitoring heavy metal enrichment and managing soil nutrients, especially AK, SOC and Fe, are important to the successful re-vegetation of the rock-cut slopes. Slow releasing fertilizers and organic fertilizers should be used to provide long-term nutrient supply for the vegetation.