Urban green spaces such as parks, gardens, and residential lawns play an essential role in supporting biodiversity, storing carbon, and improving human well-being. However, rapid urbanization is degrading these soils, reducing their fertility and disrupting natural nutrient cycles. A new study reveals that combining biochar and compost can restore soil health, but only under the right conditions, and fungi play a decisive role in determining success.
In a field experiment across three urban green spaces in Beijing, researchers investigated how biochar and compost amendments influence soil carbon storage and fertility. The study found that these treatments significantly improved soil carbon and nitrogen levels, but the benefits varied widely depending on the initial nutrient status of the soil.
"We found that fungi are the hidden drivers of soil recovery in urban environments," said the study's lead author. "By enhancing fungal communities, especially in nutrient-poor soils, we can greatly improve carbon storage and soil fertility."
The researchers observed that the positive effects of biochar and compost were up to 14 times stronger in nutrient-poor soils compared to nutrient-rich ones. In these poorer soils, the amendments increased fungal diversity and strengthened microbial networks, which helped stabilize carbon and retain nutrients. Fungi, known for their ability to break down complex organic matter and support long-term carbon storage, became more dominant relative to bacteria.
In contrast, nutrient-rich soils responded very differently. Instead of improving soil health, the amendments reduced fungal diversity and weakened microbial network stability. At the same time, bacterial growth increased, accelerating the breakdown of carbon and leading to carbon loss. This shift from fungal to bacterial dominance ultimately destabilized soil carbon pools.
"These results show that more nutrients do not always mean better outcomes," the researchers explained. "In nutrient-rich soils, added organic amendments can actually trigger faster carbon consumption rather than storage."
The study also found that combining biochar and compost did not always produce stronger results than using them separately. In some cases, especially in nutrient-rich soils, the combined treatment even reduced soil carbon and nitrogen levels. This suggests that simply adding more amendments is not enough, and that soil conditions must be carefully considered.
Urban soils are highly variable, and this research highlights the importance of tailoring restoration strategies to local conditions. The findings suggest that nutrient-poor green spaces should be prioritized for biochar and compost applications, where the ecological benefits are greatest.
Beyond practical implications, the study provides new insight into the microbial mechanisms that govern soil restoration. Fungal communities emerged as the central regulators of soil carbon storage, fertility, and ecosystem stability. Their diversity, functional traits, and network structure were closely linked to improvements in soil health.
Urban planners and land managers are increasingly looking for sustainable ways to enhance green infrastructure and combat climate change. This research suggests that managing soil microbiomes, especially by promoting fungi, could be a powerful tool for improving urban ecosystems.
By aligning soil treatments with microbial processes, cities can better restore degraded soils, increase carbon sequestration, and support healthier urban environments.
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Journal Reference: Deng, S., Gao, Q., Han, L. et al. Fungi enhance biochar and compost effects on carbon accrual in nutrient-deficient urban greenspace soils. Biochar 8, 85 (2026).
https://doi.org/10.1007/s42773-026-00599-8
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
