Long-term protection in grasslands enhances soil carbon storage via reduced disturbance and community trait diversity-environment adaptations

Understanding how ecological disturbance and plant community traits regulate soil carbon storage is critical for predicting ecosystem feedbacks to global change and designing sustainable land-use strategies. However, the processes by which disturbance regimes mediate the trade-offs between species preservation and soil carbon storage are difficult to predict due to their complexity and remain debated, particularly in comparison to protected systems. We employed a paired-site design, sampling 30 long-term managed grasslands and their paired nature reserve counterparts across a gradient of three grassland types (wet, mesic, and dry) in Central Europe (Czechia). At each site, we quantified soil carbon stocks, characterized soil chemical properties, measured aboveground biomass production, and assessed plant community composition through species diversity and functional trait analyses. We found that protected grasslands store significantly more carbon than their conventionally managed counterparts, driven by reduced anthropogenic disturbances, which promote ecosystem stability and enhance nutrient retention, coupled with plant community traits that favour carbon storage. Our results show that dry grasslands accumulated more carbon than mesic or wet types, likely due to trait-mediated stabilization and constrained microbial activity under aridity. Despite higher biodiversity in protected areas, soil carbon stocks were uncorrelated with species richness, revealing a potential indirect decoupling of species richness and carbon sequestration. Notably, biomass-carbon correlations persisted in managed grasslands but vanished in protected systems, indicating divergent dynamics of productivity from storage under undisturbed conditions. The environmental indicators predicted carbon stocks in protected grasslands, whereas managed systems relied on community characteristics and acquisitive traits. This study demonstrates that protected grasslands support both richer biodiversity and larger soil carbon stocks compared to commercially managed sites. The findings that underscore the ecological benefits of sustained protection and limited disturbance, providing valuable insights for land management and restoration strategies within existing conservation programs that integrate biodiversity protection with carbon sequestration, such as the Natura 2000 Network.