Organic amendment practices as possible drivers of biogenic Volatile Organic Compounds emitted by soils in agrosystems

We investigated whether perennial soil organic amendments of pig slurry (PS) and methanized pig slurry (MPS) affect active bacterial communities and change the diversity and the C-flux of Volatile Organic Compounds (VOCs) emitted by soils compared to control plots without any fertilization (C). The long term effects of the fertilization history of the amendments and the short term impact of the organic inputs were both investigated by measuring VOCs emissions using a Proton Transfer Reaction-Mass Spectrometer (PTR-MS) and by analyzing active bacterial diversity by MiSeq Illumina sequencing just before and up to 64 days following the inputs. Soil VOCs emissions (diversity and fluxes) naturally varied with temperature and rainfall variations, irrespective of manure inputs. No effect of the 5-yr fertilization history was observed on bacterial communities' composition and on soil VOCs emissions. However, both manure inputs (PS and MPS) were associated with an inoculation of gamma-Proteobacteria (Pseudomonas sp. and/or Marinospirinum sp.) to the soil on top of which PS inputs activated native soil Bacillus sp. (Firmicutes). VOCs spectra was mainly dominated by methanol and acetonitrile, the acetonitrile emissions not depending on the organic practices. C-VOCs fluxes from the soil to the atmosphere varied from 12 to 76 mu g of C-VOCs h(-1) m(-2) in the control plots. Pig slurry and methanized pig slurry differentially impacted soil VOCs emissions: PS inputs doubled the C-VOC fluxes due to high emission of methanol while MPS inputs reduced VOCs fluxes even less than the control unamended plots, which is of great interest in the context of mitigating greenhouse gases in agriculture. Our results suggest that soil fluxes could, under certain conditions, not be marginal compared to plant fluxes and be potentially driven by new land-uses in agriculture.