Plant and soil microbiomes are key drivers of agroecosystem function, especially the retention and cycling of nutrients. Individual plant species will uniquely shape soil microbiomes based on their life-history traits and environmental conditions, but what is the impact of growing plants in combination? In this study, we assessed soil microbial trajectories when three common cover crops (CCs) with distinct life-history traits were grown in monocultures or in mixtures across different nitrogen (N) amendment concentrations. CC mixtures were expected to generate soil microbiomes that reflect antagonistic and/or synergistic relationships among plants rather than simply additive based on the relative influence of each plant species. Canola, clover, and triticale were grown in monoculture, biculture, and triculture, and analysed across two N fertilization levels for soil microbial biomass and composition, plant growth, and nutrient concentrations of plants and soil. Bicultures containing triticale had higher soil microbial biomass than other bicultures. These patterns were nutrient-dependent; for example, triticale monoculture averaged higher microbial biomass in moderate N (21 μg PLFA g soil -1 g biomass -1 ) than in high N conditions (14 μg PLFA g soil -1 g biomass -1 ). The CC treatments significantly shifted fungal composition where canola-containing pots differed significantly from other pots in the high and moderate N treatments, indicating that canola had a disproportionate influence on soil fungal microbiome modification. Our results suggest that differences in plant life-history traits within cover crop mixtures may influence shifts in the belowground recruitment of soil microbes, which further varies with nutrient changes.
Isbell et al. (Mon,) studied this question.