Long-term impact of 19 years’ farmyard manure or sewage sludge application on the structure, diversity and density of the protocatechuate-degrading bacterial community

Impact of long-term biosolids application on soil-living micro-organisms key players of ecosystemic services is scarcely reported. Here, the impact of the 19 year-long application of farmyard manure (FM) and sewage sludge (SS) organic fertilisation regimes on the protocatechuate-degrading bacterial (pca) community was estimated by comparison to a mineral fertilisation regime (U). The structure, diversity and density of the pca community were determined using pcaH, a gene encoding the protocatechuate 3,4-dioxygenase. Ten years after the last application, the structure of the pca community in soils amended with SS100 (100 t/ha/2 years) and to a lesser extent with FM (10 t/ha/year) was still different from that in U treatment. pcaH amplicons from all treatments were cloned, screened by RFLP and sequenced. The diversity was studied by Shannon–Weiner and Simpson indexes and by rarefaction curves estimated from pcaH library analyses, showing that the pcaH community was impacted in SS10 and SS100, compared to U. The sequencing of pcaH amplicons supports the results from the RFLP analysis. Quantification of the abundance of the pca community by qPCR assays showed a significant increase in SS100 in comparison to U, FM and SS10. Overall, 10 years after the last application, the impact of 19 years’ organic fertilisation on the pcaH community was still traceable, highlighting the lack of resilience of this functional community.

► Ten years after the last amendment, impact of organic fertilisation was addressed. ► Heavy metals (Zn and Cu) were found to be accumulated in amended soils. ► Impact on protocatechuate-degrading (pca) bacteria was addressed. ► Shifts in pca community structure and abundance were correlated to Zn and Cu contents. ► Ten years after the last organic application, the pca community is still impacted.