White clover promotes microbial necromass formation in grassland mixtures

Plant species mixtures are widely promoted to enhance soil carbon sequestration, yet their effects on microbial carbon stabilization remain poorly understood. We evaluated living microbial biomass using phospholipid fatty acids and microbial necromass using amino sugars in perennial grasslands differing in species richness and composition. Treatments included perennial ryegrass ( Lolium perenne L.) monocultures and mixtures containing white clover ( Trifolium repens L.) and additional grassland species. Living microbial biomass tended to increase with plant diversity, whereas microbial necromass showed contrasting patterns. The perennial ryegrass–white clover mixture accumulated the highest amino sugar content and bacterial necromass and exhibited the greatest relative microbial stabilization and necromass accumulation coefficient, indicating enhanced accumulation of microbial residues relative to living biomass. In contrast, 6‐ and 18‐species mixtures did not increase necromass accumulation. These findings suggest that species identity, particularly white clover, exerts stronger control over microbial residue formation than plant diversity per se, with potential implications for longer term soil carbon formation and persistence.