Effects of bio-based residue amendments on greenhouse gas emission from agricultural soil are stronger than effects of soil type with different microbial community composition

With the projected rise in the global human population, agriculture intensification and land-use conversion to arable fields is anticipated to meet the food and bio-energy demand to sustain a growing population. Moving towards a circular economy, agricultural intensification results in the increased re-investment of bio-based residues in agricultural soils, with consequences for microbially mediated greenhouse gas (GHG) emission, as well as other aspects of soil functioning. To date, systematic studies to address the impact of bio-based residue amendment on the GHG balance, including the soil microorganisms, and nutrient transformation in agricultural soils are scarce. Here, we assess the global warming potential (GWP) of in situ GHG (i.e., CO₂, CH₄, and N₂O) fluxes after application of six bio-based residues with broad C : N ratios (5–521) in two agricultural soils (sandy loam and clay; representative of vast production areas in north-western Europe). We relate the GHG emission to the decomposability of the residues in a litter bag assay and determined the effects of residue input on crop (common wheat) growth after incubation. The shift in the bacterial community composition and abundance was monitored using IonTorrent^TM sequencing and qPCR, respectively, by targeting the 16S rRNA gene. The decomposability of the residues, independent of C : N ratio, was proportional to the GWP derived from the GHG emitted. The soils harbored distinct bacterial communities, but responded similarly to the residue amendments, because both soils exhibited the highest mean GWP after addition of the same residues (sewage sludge, aquatic plant material, and compressed beet leaves). Our results question the extent of using the C : N ratio alone to predict residue-induced response in GHG emission. Taken together, we show that although soil properties strongly affect the bacterial community composition, microbially mediated GHG emission is residue dependent.