查看更多>>摘要：? 2022 The AuthorsNitrogen (N) inputs to agricultural systems contribute substantially to soil nitrate (NO3?) concentrations, which increase NO3? leaching and contamination of groundwater. The influence of soil microbes in regulating NO3? concentrations in the topsoil are well studied but it is often assumed that microbial regulation of NO3? concentrations in the subsoil is negligible. The aim of this study was to test this assumption by determining the relationships between microbial properties and NO3? concentrations in both the subsoil and the topsoil. We measured the size of the mineralizable N (Nm) pool, microbial properties (microbial biomass, bacterial richness), nitrifier gene abundance (amoA gene copy number), denitrifier gene abundance (nirK and nirS gene copy number), denitrifier enzyme activity and NO3? concentrations in the topsoil and the subsoil in a well-drained stony soil under an established lucerne crop. We used structural equation modelling (SEM) to identify and compare the linkages of microbial properties with NO3? concentrations at each depth. In the topsoil, we found higher Nm, gene abundance, denitrification enzyme activity, bacterial richness, and microbial biomass than those in the subsoil, but there were no relationships between these variables and NO3? concentrations in the topsoil (the SEM model explained 0.06% of the variability in NO3? concentrations). In contrast, in the subsoil, NO3? concentrations were strongly correlated with bacterial amoA abundance and denitrification enzyme activity, with both variables associated significantly with Nm. We found that bacterial richness was also associated with Nm in the subsoil. Our findings highlight that microbial properties are associated with NO3? concentrations in the subsoil (the SEM model explained 82% the variability in NO3? concentrations) and this suggest that nitrification and denitrification may contribute to regulating NO3? concentrations in the subsoil. Our findings also suggest that denitrification contributes to reducing NO3? concentrations in the subsoil. We conclude that studies addressing drivers of NO3? leaching need to consider the potential for microbially-mediated attenuation (or an increase) in NO3? concentrations throughout the soil profile.
查看更多>>摘要：? 2022 Elsevier B.V.Manure application improves soil productivity but also spreads microorganisms, some of which can be of clinical relevance. The ability of manure to spread common human pathogens has been widely studied but we lack understanding on whether it also disseminates opportunistic pathogens like Acinetobacter and other non-fermenting Gram-negative bacteria (NFGNB). We designed a microcosm experiment simulating the application of fresh manure to soil to analyse the effects on soil microbial communities (and vice versa), focusing on Acinetobacter and other NFGNB. We conducted two independent experiments with fresh cattle manure from a dairy farm and two pasture soils from different organic farms. We sampled the microcosms on days 2, 7, 14, 28 and 84, and characterized the microbial communities through sequencing of 16S rRNA amplicons from i) total communities and ii) those cultured on CHROMagar Acinetobacter (i.e., selective for NFGNB) after 24-h growth. Manure altered the community composition of soil microorganisms whereas the reverse effects were weaker, showing a transition to an environmentally structured community. Acinetobacter species increased their relative abundance in manure and soil under manure on day 2, especially in soils previously exposed to γ-irradiation to reduce the load of native microorganisms. Although manure spread most Acinetobacter phylotypes in the soil, it also stimulated a few from the soil that became occasionally abundant in manure. This study demonstrates that Acinetobacter species may dominate in soil and manure for a short time after deposition, and highlights their high responsiveness and competitiveness to changes likely associated with an increase in labile resources.
NSTL
Elsevier