Short-term effects of biochar amendment on root–microbe interactions in natural and peri-urban soils

Peri-urban areas are increasingly exposed to multiple environmental and anthropogenic threats that alter root-microbe interactions and compromise overall ecosystem stability. The short-term effect of biochar amendment on rhizoplane and rhizosphere interactions was investigated as an effective mitigation strategy, through rhizobox experiments. The higher pH, nutrient content, and metal(loid) concentrations in peri-urban soils compared to non-urban soils, lead roots to invest more in diameter and structural robustness rather than in exploratory growth, alongside a complex diversity in microbial communities. Biochar markedly affected the rhizosphere interactions in both non-urban and peri-urban soils by strengthening correlations among microbial taxa, soil nutrients, and root traits, while reinforcing pre-existing root development strategies. In the rhizoplane, biochar promoted new correlations between key microbial genera and soil/root features, likely creating microhabitats that support nitrogen cycling and plant growth-promoting interactions. Taken together, biochar appears to be an affordable mitigation strategy for improving root and microbial functional stability.