Linking soil microbial carbon sequestration to cover crop diversification in agricultural soil systems across Europe

Sequestering atmospheric CO₂ into soil organic matter through changes in agricultural practices is an appealing idea to improve soil ecosystem services and to improve global change mitigations. The old view of carbon (C) stability in soil, based on the intrinsic properties of the organic matter inputs (e.g. lignin content), would lead policy towards greater percentages of recalcitrant organic matter content in crops. Recent research suggests otherwise and that managing how the soil microbiome process C inputs is a more fruitful approach (Sokol et al., 2019, Poeplau et al., 2019). It is therefore to decipher and evaluate the link between the aboveground plant community and the complex belowground diversity of the microbiome and their metabolic processes that mediate C sequestration. Lehmann et al. (2020) proposed a theoretical framework in which the persistence of C in soil can be understood as the outcome of interactions between the molecular variability of organic matter input and spatio-temporal microbial heterogeneities of the soil system.

Within the EnergyLink framework we therefore investigate various microbial markers to illuminate possible physiological changes across several European agricultural field sites with different cover crop management types. Specifically, for detecting shifts in microbial necromass composition and quantity we target amino-sugars (galactosamin, gluctosamine, mannosamine and muramic acid), for evaluating effects on growth rates we measure ¹⁴C incorporation into ergosterol for fungi and ¹⁴C-leucine incorporation for bacteria and to grasp changes in uptake strategies we test extra cellular enzyme activities for different nutrient classes. Additionally, we determine C:N:P ratio for bulk soil, microbial biomass and above ground plant biomass to estimate stoichiometric imbalances. Here we present results from our first sampling campaign and discuss implications of diversified cover crops on soil carbon properties on a European scale.