Shifts in Soil Bacterial Diversity and Abundance at Various Taxonomic Levels in Tropical Peatlands Under Land-Use Change.

Tropical peatlands are among the largest global carbon sinks and face increasing impacts from drainage, fire, and land-use change. These disturbances modify soil physicochemical characteristics and influence bacterial community structure. However, the response of bacterial communities to these changes is incompletely understood. This study examined bacterial community composition at six peatland sites in the Giam Siak Kecil-Bukit Batu Biosphere Reserve, Riau, Indonesia. The sites represent various land-use types: secondary forest, restored peat, burned peat, oil palm, rubber, and acacia plantations. The analysis employed 16S rRNA gene sequencing combined with measurements of soil physicochemical properties. Results showed that key bacterial phyla, such as Acidobacteriota, Pseudomonadota, and Actinomycetota, were consistently found across sites, though their relative abundances varied. Burned sites had increased abundances of Bacillota and other copiotrophic groups and decreased abundances of several oligotrophic taxa. Beta diversity analysis showed differences in community patterns among sites, but multivariate analysis did not show significant differences between land-use types. Variation in bacterial community composition is associated with soil pH and nutrient availability, including available phosphorus, exchangeable potassium, and exchangeable magnesium, although these relationships are not always statistically supported. A small number of ASVs were detected across all sites, suggesting overlapping community members amid high spatial heterogeneity. Overall, tropical peatland bacterial communities form within a narrow environmental framework in which distinctive physicochemical properties constrain which microbes can survive. Land-use changes are primarily associated with shifts in the relative abundance of bacterial taxa rather than complete community turnover. Given the limited number of samples and single time-point observations, these findings are exploratory and provide a basis for further research.