Bacterial and Archaeal Communities in Bleached Mottles of Tropical Podzols

Podzols frequently show bleached mottles depleted in organic matter, most readily visible in the Bh horizons. Even though the process of bleached mottles development is not understood, it has been suggested that the selective degradation of organic matter by soil microorganisms has a major contribution. In this study, we examined the bacterial and archaeal communities along three Brazilian coastal podzol profiles, as well as in bleached mottles and their immediate vicinity, using 16S rRNA gene profiling. Our results showed that the bacterial and archaeal community structures in the studied podzols varied with depth and that the bacterial communities in the bleached mottles were significantly different from that in their immediate vicinity. In contrast, the archaeal communities in bleached mottles were significantly different from their vicinity only in the Bertioga (BT) profile, based on sequencing of amplicons of the 16S rRNA gene. Redundancy analyses showed that the bacterial community structures in the bleached mottles of BT were negatively associated mostly with the levels of organic carbon, exchangeable-aluminum (Al), exchangeable potassium, and Al-saturation, whereas in the surrounding soil, the opposite was observed. In the Ilha Comprida (IC) profiles, no such relationships were observed, suggesting distinct drivers of the bacterial community structures in bleached mottles of different podzols. In the bleached mottles of the BT profile, operational taxonomic units (OTUs) phylogenetically related to Pseudomonas were the most abundant Bacteria, whereas in the IC profiles, OTUs related to Acidobacteria were predominant. Thermoprotei (Crenarchaeota) were the most abundant Archaea in the bleached mottles and in their immediate vicinity. Based on the diverse metabolic capabilities of Pseudomonas and Acidobacteria, our data suggest that these groups of bacteria may be involved in the development of bleached mottles in the podzols studied and that the selection of specific bacterial populations in the bleached mottles may depend on the local edaphic conditions.