Cover crops influence aboveground and belowground invertebrates in farmlands

1. Maintaining vegetation diversity through cover crops could counteract the decreasing soil carbon and biodiversity in intensive monoculture farming, but its impacts on fauna have rarely been quantified. 2. To investigate how cover crops influence the abundance and trophic structure of invertebrates, or inorganic N (proxy of soil functioning), barley (Hordeum vulgare) was grown with up to eight undersown cover crops. Soil fauna (nematodes, enchytraeids and earthworms), slugs, and arthropods living on soil surface, vegetation, and barley were sampled, and soil inorganic N availability measured. 3. Cover crops increased the abundance of aboveground and belowground invertebrates compared to barley monoculture. The proportion of predatory arthropods increased, suggesting that cover crops improved the potential for biological control. 4. Cover crop functional traits (N2-fixation and deep roots) had selective effects. For example, legumes increased soil inorganic N availability and the abundance of aboveground herbivores, while deep-rooted species benefited earthworms. The species richness of cover crops did not affect invertebrates or soil N. 5. Synthesis and applications: Our results suggest that cover crops can improve agroecosystem diversity and functioning, and that significant effects on invertebrate-mediated ecosystem functions such as biological control can already be achieved at low levels of added vegetation diversity.