Both biotic and abiotic management strategies facilitate biomass recovery and CO2 absorption: evidence from three experiments in southern grasslands

Background The southern grasslands of China sustain substantial livestock but face functional degradation due to overuse. The carbon flux responses to restoration strategies remain unclear. Methods In this study, we implemented a three-year restoration experiment in artificial grasslands using three approaches: reseeding (D: Dactylis glomerata monoculture, T: Trifolium repens monoculture, DT: their mixture), chemical fertilization (NP _L /NP _M /NP _H : nitrogen 2/4/8 g m⁻² + phosphorus 0.7/1.4/2.8 g m⁻²), and biofertilization with Burkholderia sp.(B ₃₀ /B ₆₀ /B ₁₂₀ : 30/60/120 g m⁻²). Results All treatments increased grassland biomass. Specifically, NP _H significantly enhanced above-ground biomass, while D, B _30, and NP _L notably boosted below-ground biomass. D, NP _L , NP _H , and B ₃₀ significantly increased total biomass. Restoration treatments usually had a negative effect on NEE, with DT (β = -0.383, P  = 0.020), NP _L (β = -0.350, P  = 0.027), NP _M (β = -0.422, P  = 0.008), and B ₆₀ (β = -0.341, P  = 0.029) showing significant effects. However, they exhibited positive effects on both ER and GPP. Specifically, NP _L , NP _M , NP _H , B ₃₀ , B ₆₀ , and B ₁₂₀ significantly enhanced ER (β = 0.290 to 0.525, P  = 0.001 to 0.049), while all measures except T significantly increased GPP (β = 0.297 to 0.613, P  < 0.001 to 0.048). Dissolved organic carbon, available phosphorus, and biomass contributed to the changes in carbon sequestration. Conclusion Our results demonstrate that both traditional fertilization and alternative strategies like reseeding and biofertilization can effectively restore grassland productivity and carbon sequestration capacity, providing multiple pathways for sustainable grassland management.