Plant diversity is key for microbial necromass carbon accrual in alpine grasslands

The positive effect of plant diversity on soil carbon (C) stocks is well documented, yet its role in shaping persistent C components essential for long-term soil C stability remains unclear. Using a 3,000-km transect survey of natural grasslands, we found that both bacterial and fungal necromass C increased with plant species richness, with more pronounced effects in the topsoil than in the subsoil and a steeper increase in fungal-derived necromass. Plant C inputs emerged as the primary driver of this response, exerting a stronger influence than soil nitrogen, pH, microbial attributes or mineral properties. These findings indicate that plant diversity promotes persistent soil C accumulation primarily through substrate supply that enhances microbial residue production. Our study underscores the importance of maintaining and restoring plant diversity in grasslands as a nature-based strategy to enhance stable soil C storage, thereby facilitating soil C sink capacity and contributing to climate change mitigation. Soil bacterial and fungal necromass carbon is linked with plant species richness with a stronger positive correlation in the topsoil than in the subsoil, according to observations along a 3,000 km transect in grasslands on the Tibetan plateau.