Linking Soil Organic Carbon Dynamics and Selective Bacterial Carbon-Cycling Enzyme Functionality Across Ecosystems: High-Performing Bacillus Isolates Can Potentially Improve Soil Carbon Dynamics and Plant Growth

Soil organic carbon (SOC) dynamics are critical to ecosystem functioning and sustainable agriculture, yet the microbial mechanisms responsible for SOC turnover remain underexplored across diverse landscapes. This study investigates SOC distribution and microbial carbon (C)-cycling functionality across hill forest, piedmont, and coastal plain ecosystems along an elevation gradient in the Teknaf Peninsula, Bangladesh. Through ecosystem-scale soil analysis and isolation of 51 native bacterial strains, we evaluated C fractions, soil biochemical traits, and five selective C-cycling enzymatic activity profiles of key extracellular hydrolytic enzymes. Results revealed significantly higher SOC, acidity, nitrogen (N), carbohydrates, and recalcitrant C in hill forest soils, while coastal plains exhibited higher β-glucosidase activity and potassium (K) availability. The highest enzymatic potential for four of the five enzymes examined (amylase, cellulase, protease, and β-glucosidase) was exhibited by hill forest isolates, whereas the highest xylanase potential was observed in a piedmont isolate. Although 9 of the 17 coastal plain isolates exhibited multiple-enzymatic activities (tested positive for two enzymes or more), none showed the highest potential for any specific enzyme. Eight highest-performing, multifunctional isolates were selected for bioinoculant consortium development, and 16S rRNA gene sequencing identified all isolates as Bacillus spp. A consortium of these Bacillus isolates significantly enhanced jute (Corchorus olitorius) growth (21%–92% increase) in pot trials and helped maintain elevated SOC (13%–19% increase) and labile C levels (11%–176% increase) throughout the cropping period. These findings highlight the potential of native bacterial consortia to support plant productivity and C retention in soils. The integration of microbial functional traits with ecosystem-specific soil dynamics offers a promising pathway toward eco-friendly soil management strategies and sustainable agriculture.