Legume and Non-legume Cover Crops Shape Distinct Soil Microbial Communities and C-cycling Functional Traits

Winter cover crops are commonly used as a source of nutrients in organic production. However, the impact of these crops on soil microbial functional traits at the genomic level is poorly understood.Here, we investigated the impacts of three-year inclusion of cereal rye (Secale cereale L), hairy vetch (Vicia villosa), and their mixture on soil microbial diversity and residue decomposition functional traits using 16 S rRNA gene and internal transcribed spacer (ITS) sequencing data and functional prediction tools. Integrating a mixture of rye and vetch increased bacterial richness and alpha diversity but had no impact on fungal diversity when compared to the control. The fungal community structure of the soils with either rye or vetch inclusion was significantly different from that of the mixture and the control. Compared to vetch, rye inclusion was predicted to have a significantly higher abundance of C1 compound utilization and assimilation pathways, but a lower abundance of amino acid degradation and carboxylic acid degradation pathways. Similarly, rye inclusion resulted in a significantly higher abundance of arbuscular mycorrhizae but a lower abundance of litter saprotrophs than vetch inclusion. Particularly, integrating vetch was predicted to have a significantly higher abundance of genes involved in cellulose and lignin decomposition than the rye inclusion. Five keystone cellulose and lignin bacterial decomposers were significantly more abundant with vetch inclusions than with rye inclusions. Nonlegume and legume winter cover crops imposed distinct effects on soil potential microbial C-cycling functional traits after three planting seasons. Legumes favored the growth of microbial decomposers compared to non-legumes.