Combining diversified prairies with wheat to promote beneficial plant-soil ecological interactions and the coupling of carbon and nitrogen biogeochemical cycles in agroecosystems

Mobilizing plant functional diversity appears as a promising avenue to promote agroecosystems multifunctionality and stability in order to face agriculture challenges in terms of production, limitation of inputs, conservation of soils, and mitigation of greenhouse gases emissions. In natural or semi-natural ecosystems, a high level of plant functional diversity might trigger beneficial plant-soil ecological interactions, leading to several mechanisms of coordination over time between plant nutrient demand and soil offer (i.e., “synchrony”). As perennial prairies can reach a considerable degree of functional diversity within a small area, their implementation with crops can be a precious lever to promote such mechanisms. Among those, a seasonal scale coordination between plants nutrient demand and the relative balance between microbial construction and microbial decomposition of Soil Organic Matter (SOM) was associated with prairies encompassing fast-growing species. This leads to improved plant primary productivity combined with reduced nutrient losses, and increased microbial originated carbon (C) storage in the soil. Moreover, the modulation of nitrogen (N) symbiotic fixation depending on photosynthesis activity by legumes within the prairies allows N enrichment of the agroecosystem.

We conceived an experimental design with new agroecosystems called “agroprairies” which gather perennial diversified prairies and winter wheat (Triticum aestivum) cultivated in alternating bands. Four functionally different prairies were designed to vary across nutrient acquisition strategies and proportion of legumes. The experiment also included plots with each cover grown alone, as well as a perennial crop (Thinopyrum intermedium). We explored the effects of plant functional diversity on soil biogeochemical C and N cycles and soil microbial communities and activities. We conducted measurements of plant production, soil microbial C dynamics (microbial C use efficiency, soil microbial respiration, microbial biomass, microbial growth), five hydrolytic or oxidative exoenzyme activities related to C, N and phosphorus (P) cycles and abundances of the soil microbial communities (bacteria, archaea and fungi). These measurements were performed in January 2024 during winter at a time where plant nutrient demand is low, and in May 2024 at the maximum plant biomass production. We found that soil biogeochemical C and N cycles and abundances and activities of microbial communities strongly varied between January and May, and that some of these variables, as well as the production of wheat differed depending on the functional characteristics of the prairies.