Date Published: December 11, 2014
Publisher: Public Library of Science
Author(s): Yuanyuan Li, Hongyu Wen, Longqian Chen, Tingting Yin, Daniele Daffonchio.
The growing concern about the effectiveness of reclamation strategies has motivated the evaluation of soil properties following reclamation. Recovery of belowground microbial community is important for reclamation success, however, the response of soil bacterial communities to reclamation has not been well understood. In this study, PCR-based 454 pyrosequencing was applied to compare bacterial communities in undisturbed soils with those in reclaimed soils using chronosequences ranging in time following reclamation from 1 to 20 year. Bacteria from the Proteobacteria, Chloroflexi, Actinobacteria, Acidobacteria, Planctomycetes and Bacteroidetes were abundant in all soils, while the composition of predominant phyla differed greatly across all sites. Long-term reclamation strongly affected microbial community structure and diversity. Initial effects of reclamation resulted in significant declines in bacterial diversity indices in younger reclaimed sites (1, 8-year-old) compared to the undisturbed site. However, bacterial diversity indices tended to be higher in older reclaimed sites (15, 20-year-old) as recovery time increased, and were more similar to predisturbance levels nearly 20 years after reclamation. Bacterial communities are highly responsive to soil physicochemical properties (pH, soil organic matter, Total N and P), in terms of both their diversity and community composition. Our results suggest that the response of soil microorganisms to reclamation is likely governed by soil characteristics and, indirectly, by the effects of vegetation restoration. Mixture sowing of gramineae and leguminosae herbage largely promoted soil geochemical conditions and bacterial diversity that recovered to those of undisturbed soil, representing an adequate solution for soil remediation and sustainable utilization for agriculture. These results confirm the positive impacts of reclamation and vegetation restoration on soil microbial diversity and suggest that the most important phase of microbial community recovery occurs between 15 and 20 years after reclamation.
Mining activities result in extensive soil damage, causing drastic disturbances in landscape, altering the ecological environment of soil microorganisms, thereby disrupting the functional stability of the microbial community . The ultimate goal of mine land reclamation is the reestablishment of a productive, healthy and sustainable ecosystem suitable for post-mining land use , . Because of the important ecosystem functions mediated by microorganisms in the soil, recovery of the soil microbial community is a critical step in achieving the goal of soil restoration for its sustainable and beneficial use . Currently, criteria for successful restoration have largely been restricted to soil erosion, physicochemical status and vegetation characteristics –. Analysis of microbial ecological indicators such as microbial populations, microbial communities and function diversity in reclamation evaluation were relatively uncommon . Changes in microbial community can precede detectable changes in soil physicochemical properties, thereby providing early signs of environmental stress or ecological environment evolution in the mining area . Although microbial communities regulate important ecosystem processes, it is often unclear how the abundance and composition of microbial communities correlate with reclamation and interact to affect ecosystem processes. Previous studies on the effect of land reclamation have primarily focused on the physical properties, chemical characteristics, or heavy metal pollution of reclaimed mine soil –. There are few studies on general soil microbial community recovery and these studies have revolved around the effects of soil reclamation on microbial populations, microbial biomass and activity , , , . In case of mine soils, recovery of soil bacterial diversity and structure in disturbed and reclaimed lands is not well understood.
Through cultivation-independent molecular analyses, we provide an assessment of response and recovery of soil microbial communities to disturbance caused by mining reclamation. In the present work, we were able to classify 98,657(94.23%) of the 104,698 quality sequences below the domain level. The total number of analyzed sequences and the percentage of classified 16S rRNA gene sequences exceeded those of other pyrosequencing-based studies of soil bacterial community composition in restoration and mining sites -. Furthermore, at 3% distance (species level), the OTUs identified (ranged from 1136 to 2997) were greater than those reported in other 16S rRNA clone library-based studies -.
Reclamation and Re-vegetation produced a significant effect on soil bacterial diversity and community structures. In accordance with our initial hypothesis that bacterial community in older reclaimed soils would be more similar to those in natural soils, we found that bacterial richness and diversity increased significantly with increasing number of years since reclamation, recovering to pre-disturbance levels nearly 20 yrs after reclamation. There was a clear association between bacterial community and soil physicochemical properties such as SOM, TP, TN and pH. The increase of soil variables in reclaimed treatments can be attributed to the mixed-planting experiments on legumes with gramineous grass. We concluded that soil remediation and re-vegetation has indirect effects on soil microbial community diversity through their influence on soil physicochemical properties, especially nutrient elements. Our results also indicated that restoring the variability of soil physicochemical and microbial diversity level similar to the undisturbed soils requires a longer reclamation history.