Abstract
Positive relationships between plant diversity, microbial diversity, and ecosystem functioning have widely been observed in experimental grasslands. However, the impact of cover crop (CC) species diversification on soil microbial diversity and function in croplands remains underexplored. This study investigated how increasing the diversity of undersown CCs affected seasonal properties of soil microbiomes and whether these changes resulted in legacy effects on next-year crops. In barley fields undersown with functionally diverse CCs, soil samples were collected throughout the year to assess microbial properties. To evaluate legacy effects on the following year's barley, soil microorganisms were sequenced from spring samples collected before CC termination. Additionally, a pot experiment using flax was conducted to study how CC diversity influenced arbuscular mycorrhizal (AM) fungal colonization in roots. Results showed that vegetation presence and higher CC richness increased microbial biomass carbon and decreased the microbial metabolic quotient. Legumes' presence reduced microbial respiration. Fungal and AM fungal diversity also increased with CC richness, while legumes helped suppress fungal pathogens. In the pot experiment, presence of both vegetation and legumes positively influenced AM fungal root colonization. Overall, undersowing diverse CCs, particularly legumes, can increase soil microbial diversity and soil health, benefiting both the current and next-year crops.