Microbial Response to Soil Liming of Damaged Ecosystems Revealed by Pyrosequencing and Phospholipid Fatty Acid Analyses.

AIMS: To assess the effects of dolomitic limestone applications on soil microbial communities' dynamics and bacterial and fungal biomass, relative abundance, and diversity in metal reclaimed regions.

METHODS AND RESULTS: The study was conducted in reclaimed mining sites and metal uncontaminated areas. The limestone applications were performed over 35 years ago. Total microbial biomass was determined by Phospholipid fatty acids. Bacterial and fungal relative abundance and diversity were assessed using 454 pyrosequencing. There was a significant increase of total microbial biomass in limed sites (342 ng/g) compared to unlimed areas (149 ng/g). Chao1 estimates followed the same trend. But the total number of OTUs (Operational Taxonomic Units) in limed (463 OTUs) and unlimed (473 OTUs) soil samples for bacteria were similar. For fungi, OTUs were 96 and 81 for limed and unlimed soil samples, respectively. Likewise, Simpson and Shannon diversity indices revealed no significant differences between limed and unlimed sites. Bacterial and fungal groups specific to either limed or unlimed sites were identified. Five major bacterial phyla including Actinobacteria, Acidobacteria, Chloroflexi, Firmicutes, and Proteobacteria were found. The latter was the most prevalent phylum in all the samples with a relative abundance of 50%. Bradyrhizobiaceae family with 12 genera including the nitrogen fixing Bradirhizobium genus was more abundant in limed sites compared to unlimed areas. For fungi, Ascomycota was the most predominant phylum in unlimed soils (46%) while Basidiomycota phylum represented 86% of all fungi in the limed areas.

CONCLUSION: Detailed analysis of the data revealed that although soil liming increases significantly the amount of microbial biomass, the level of species diversity remain statistically unchanged even though the microbial compositions of the damaged and restored sites are different.

SIGNIFICANCE AND IMPACT OF THE STUDY: Soil liming still have a significant beneficial effects on soil microbial abundance and composition > 35 years after dolomitic limestone applications.