Soil properties influence bacterial abundance and diversity under different land-use regimes in semi-arid environments

Bacterial diversity is known to be a driver of soil ecosystem services and it is influenced by the natural integrity of the environments. Samples from garden soil, saline soil and sludge-impacted soil were studied to evaluate the influence of soil properties on bacterial abundance and diversity for improved management. Soil samples were collected from 0 to 15 cm depth and analyzed for selected physico-chemical properties using routine laboratory procedures. 16S rRNA gene-based metagenomics analysis was used to identify and quantify bacteria from the samples. Garden soil had pH (H₂O) of 5.8, electrical conductivity (EC) of 0.3 dS m⁻¹, organic matter (OM) content of 0.66%, total phosphorus (P) and cation exchange capacity (CEC) of 132 ppm and 2.40 Cmol kg⁻¹, respectively, and 8.39% clay; sludge impacted soil had a pH (H₂O) of 5.8, EC of 5.7 dS m⁻¹, OM content of 57.5%, 2641 ppm P, CEC content of 8.62 Cmol kg⁻¹ and 18.23% clay; while salt affected (saline) soil had a pH (H₂O) of 7.6, EC of 4.4 dS m⁻¹, OM of 0.5%, P content of 24.9 ppm, CEC of 4.05 Cmol kg⁻¹ and 13.07% of clay contents. The distribution of bacteria phyla identified in the soils is as follows: sludge-impacted soil (15), garden (13) and bare saline (10). Next generation sequencing shows that five of the phyla in the order Proteobacteria > Actinobacteria > Firmicutes > Bacteroidetes > Acidobacteria were present and dominant in all the soils. Soils under the different land uses significantly varied in their properties. It is concluded that bacterial diversity was influenced by the degree of habitat disturbance caused by variation in land-use management practices which affected properties of the soils. This study opens up new frontiers in expanding metagenomics studies in the semi-arid environments of Botswana and contributes to the identification of soil bacteria which are useful to ecosystem functions.