Changes in weathering effectiveness and community of culturable mineral-weathering bacteria along a soil profile

Bacteria play important roles in mineral weathering, element mobilization, and soil formation. However, little is known about the mineral-weathering bacteria in subsurface soil environments. In this study, a total of 360 bacterial isolates were isolated from the different horizons of a soil profile and characterized for their mineral-weathering abilities and diversity along the soil profile. Among the 360 isolates, 226 isolates were found to have the ability to weather biotite. The average of released Fe, Si, and Al were significantly higher by the isolates from deeper horizons than from upper horizons. Although the proportion of the highly effective Fe solubilizers was not significantly different among the different horizons, the proportion of the highly effective Si and Al solubilizers was significantly higher in the deeper horizons than in the upper horizons. Furthermore, the element-releasing patterns of the mineral-weathering bacteria were different among the different horizons. Most of mineral-weathering bacteria from the soil profile could significantly lower the culture medium pH in the mineral-weathering process. The diversity of the mineral-weathering bacteria was higher in the upper horizons than in the deeper horizons. The weathering bacteria belonged to 12 bacterial genera, among which Burkholderia, Bacillus, and Lysinibacillus were the dominant and high-efficient weathering bacteria. The results showed the depth-related changes in the weathering capacity and community structures of the culturable mineral-weathering bacteria and suggested the possible roles of the bacteria in the mineral-weathering and element mobilization along the soil profile.