Underground ecosystems — and the fungi they contain — have been overlooked in climate solutions, biodiversity assessments, and conservation targets for too long. Fungal communities play a key role in regulating biodiversity, climate, and global nutrient cycles. Mycorrhizal fungi move carbon and nutrients across ecosystems, drawing down ~13 billion tons of CO2 per year. And yet an overwhelming majority of mycorrhizal biodiversity hotspots — and the vast carbon sinks they safeguard — remain unprotected.