Regulating soil bacterial diversity, community structure and enzyme activity using residues from golden apple snails

It has been shown that the golden apple snail (GAS, Pomacea canaliculata), which is a serious agricultural pest in Southeast Asia, can provide a soil amendment for the reversal of soil acidification and degradation. However, the impact of GAS residue (i.e., crushed, whole GAS) on soil bacterial diversity and community structure remains largely unknown. Here, a greenhouse pot experiment was conducted and 16S rRNA gene sequencing was used to measure bacterial abundance and community structure in soils amended with GAS residue and lime. The results suggest that adding GAS residue resulted in a significant variation in soil pH and nutrients (all P < 0.05), and resulted in a slightly alkaline (pH = 7.28-7.75) and nutrient-enriched soil, with amendment of 2.5-100 g kg^-1 GAS residue. Soil nutrients (i.e., NO₃-N and TN) and TOC contents were increased (by 132-912%), and some soil exocellular enzyme activities were enhanced (by 2-98%) in GAS residue amended soil, with amendment of 1.0-100 g kg^-1 GAS residue. Bacterial OTU richness was 19% greater at the 2.5 g kg^-1 GAS residue treatment than the control, while it was 40% and 53% lower at 100 g kg^-1 of GAS residue and 50 g kg^-1 of lime amended soils, respectively. Firmicutes (15-35%) was the most abundant phylum while Bacterioidetes (1-6%) was the lowest abundant one in GAS residue amended soils. RDA results suggest that the contents of soil nutrients (i.e., NO₃-N and TN) and soil TOC explained much more of the variations of bacterial community than pH in GAS residue amended soil. Overuse of GAS residue would induce an anaerobic soil environment and reduce bacterial OTU richness. Soil nutrients and TOC rather than pH might be the main factors that are responsible for the changes of bacterial OTU richness and bacterial community structure in GAS residue amended soil.