Fungi boost carbon storage from biochar and compost in nutrient-poor urban soils, study finds

A new field study published in Biochar shows that fungi play a critical role in whether biochar and compost amendments build long-term soil carbon or accelerate its consumption in urban greenspaces. Researchers tested three Beijing sites and found that in nutrient-poor soils, biochar and compost increased carbon and nitrogen storage up to 14.4 times more than in nutrient-rich soils. The key was a shift in microbial balance: fungi thrived, strengthening carbon retention. In nutrient-rich soils, the same amendments reduced fungal diversity and boosted bacterial growth, leading to faster carbon turnover and even net carbon loss at one site. The study suggests city managers should prioritize nutrient-poor urban greenspaces for biochar and compost interventions to maximize carbon storage and soil fertility gains. This challenges the assumption that richer soils always benefit more from organic inputs.