Bacterial community structure and putative nitrogen-cycling functional traits along a charosphere gradient under waterlogged conditions

Unique spatial niches created by biochar form a dynamic biogeochemical soil zone, termed the charosphere. Charosphere soil has different properties from either soil or biochar, often acting as a hotspot for microbial activity. However, the direction and magnitude of charosphere effects on soil processes and microbial communities remain inconclusive. Herein, we designed a multi-sectional box to separate charosphere soils from biochar under waterlogged conditions, investigating millimeter-scale changes in bacterial communities and distributions of specific genera across the charosphere created by pristine biochar (produced from corn stover at 300 degrees C), acid-modified biochar and washed biochar. The pristine biochar did not increase bacterial alpha-diversity but altered bacterial composition by promoting the growth of specific bacterial taxa and suppressing other species. In comparison, washed and acid-modified biochar increased the bacterial alpha-diversity. The pristine biochar significantly decreased N2O emission and NO3- concentration owing to a lower soil nitrification potential. Abundances of N-cycling functional taxa were higher in the near-charosphere than outer-charosphere zone, especially for Bacillus (N-2-fixation), MND1 (ammonia oxidation) and Rhodopseudomonas (denitrification). The spatial distribution of functional genes and genera documents the importance of heterogeneity within the charosphere gradient, providing a novel perspective into functional geometry to understand how biochar reduces N losses from agroecosystems.

Automated summary

The unique spatial niches created by biochar form a dynamic biogeochemical soil zone known as the charosphere. This zone has different properties from regular soil or biochar, and can act as a hotspot for microbial activity. The effects of charosphere on soil processes and microbial communities are still unclear, but the study showed that different types of biochar can have varying impacts on bacterial diversity and composition. The spatial distribution of functional genes and genera within the charosphere gradient highlights the importance of heterogeneity in understanding how biochar can reduce nitrogen losses in agroecosystems.