A long-term hybrid poplar plantation on cropland reduces soil organic carbon mineralization and shifts microbial community abundance and composition

- Converting cropland to long-term hybrid poplar plantation reduced SOC mineralization.
- Long-term hybrid poplar plantation caused lower microbial biomass and enzyme activity.
- Long-term poplar plantation decreased bacterial but increased fungal abundance.
- Changes in microbial community abundance and composition were responsible for the SOC mineralization.

Poplar plantations have been established around the world to provide timber or fuelwood and to control erosion in degraded areas. The objective of this study was to investigate the effects of converting croplands to long-term hybrid poplar (Populus × euramericana cv. I-72) plantations for 10, 15 and 20 years on soil bacterial and fungal communities and on their relationships with soil organic carbon (SOC) mineralization. Overall, the results indicated that the long-term hybrid poplar plantations increased soil pH, SOC, total N and moisture contents and decreased dissolved organic carbon (DOC), NH4+ and NO3− contents compared to that on the cropland. There were lower cumulative amounts of CO2 respired and SOC mineralization rates in the hybrid poplar plantation soils compared to that of the cropland. The hybrid poplar plantation with 20 years caused a greater fungal internal transcribed spacer (ITS) gene copy number and a lower bacterial 16S rRNA gene copy number and dehydrogenase and β-glucosidase activities compared to that in the cropland soils. As indicated by Illumina MiSeq sequencing, the establishment of hybrid poplar plantations harbored distinct soil bacterial and fungal communities, which were strongly correlated with specific soil properties. We further found that the SOC mineralization rate was positively correlated to the bacterial abundance and the relative abundances of Actinobacteria and Bacteroidetes, whereas negatively correlated to the fungal abundance. This study suggested that the long-term hybrid poplar plantation reduced SOC mineralization, causing changes in habitats that favor fungal community growth and shifts in bacterial community composition to more facultative and/or obligate anaerobes and less microbes that are capable of decomposing recalcitrant carbon, which may help enhance SOC accumulation in soil and mitigate climate change.