Functional diversity and dominant populations of bacteria in banana plantation soils as influenced by long-term organic and conventional farming

•Soil pH, organic matter content and water content positively correlated with organic farming.•Organic farming soils harbored higher functional diversity of fast-growing heterotrophs.•Distinct carbon source utilization patterns between organic and conventional farming soils were demonstrated.•More diverse uncultured bacterial phyla were revealed by clone library-based method.•Associations between metabolic activity and distribution of copiotrophic or oligotrophic populations were addressed.

A three-year field study (2012-2014) of functional diversity and dominant populations of bacteria in banana plantation soils after long-term organic and conventional farming was conducted. The pH and water content were significantly higher in 17-year and 7-year organic farming soils than that in 39-year conventional farming soils, while organic matter content and viable numbers of four bacterial groups were also slightly higher. Both organic farming soils harbored diverse functional potential and metabolic activity of fast-growing heterotrophs, as can be seen from higher substrate richness, average well color development value and diversity index. Distinct carbon source utilization patterns between organic and conventional farming soils were demonstrated through principal component analysis. A limited number of heterotrophs were isolated during 2012-2013 sampling period to obtain culturable populations, and 16S rDNA sequence analyses assigned them mainly to the phylum Firmicutes. As for 2014-collected samples more diverse uncultured phyla were revealed by clone library-based method, and members belonging to the phylum Proteobacteria were more prevalent in banana plantation soils. The predominance of copiotrophic members affiliated with β-proteobacteria and fewer clones belonging to oligotrophic Acidobacteria and α-Proteobacteria especially in 7-year organic farming soils may contribute to higher functional diversity of fast-growing heterotrophs. The present study addressed functional diversity and dominant populations of bacteria in banana plantation soils and provided insight into the influences caused by long-term organic and conventional farming.