Purpose
Rhizosphere bacteria play critical roles in soil nutrient cycling and plant growth during land reclamation. However, the impact of the type of capping material, used to provide functions such as preventing salt migration from saline groundwater to the cover soil, on rhizosphere bacterial community is unknown.
Materials and methods
We examined the influence of two capping materials: overburden (OB), a material excavated from below the top soil from oil sand mines, and tailings sand (TS), in comparison to the no capping layer (NC) control, on the composition, structure, and function of bacterial communities in the Pinus banksiana rhizosphere and bulk soil in the peat-mineral mix (PMM, the cover soil) in a 2-year column study simulating soil reconstruction in land reclamation in the oil sands. The bacterial community was determined through high-throughput sequencing the 16S ribosomal RNA (rRNA) gene amplicons, and the potential functional profiles were predicted from the 16S rRNA gene using PICRUSt.
Results and discussion
Difference in the relative abundance of operational taxonomic units (OTUs) between the rhizosphere and the bulk soil was lower in the NC and OB than in the TS treatment. Rhizosphere bacterial community structure in the cover soil was different among the NC, OB, and TS treatments. Difference in bacterial community structure between the rhizosphere and bulk soil was driven by soil pH and electric conductivity changes in the OB treatment and by water-soluble organic carbon in the TS treatment. The relative abundance of functional genes for nutrient metabolism in the rhizosphere increased in the TS treatment, but those for environmental adaption increased in the NC and OB treatments.
Conclusions
We conclude that the type of capping material used affects the structure, composition, and function of rhizosphere bacterial communities in cover soils used in land reclamation, and this has implications for ecosystem re-establishment in the disturbed landscape in the oil sands.