Impact of agricultural management on bacterial laccase-encoding genes with possible implications for soil carbon storage in semi-arid Mediterranean olive farming
- Published
- Accepted
- Subject Areas
- Agricultural Science, Environmental Sciences, Microbiology, Soil Science
- Keywords
- C sequestration, Cover crops, Olive farming, Litter decomposition, Bacterial laccase, Humic acids
- Copyright
- © 2016 Moreno et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2016. Impact of agricultural management on bacterial laccase-encoding genes with possible implications for soil carbon storage in semi-arid Mediterranean olive farming. PeerJ Preprints 4:e2097v1 https://doi.org/10.7287/peerj.preprints.2097v1
Abstract
Background . Laccases, mostly laccase-like multicopper oxidases (LMCO), are probably the most common ligninolytic enzymes in soil. Although, in recent studies, laccase-encoding genes have been successfully used as molecular markers in order to elucidate the role of bacteria in soil organic C cycling , further research in this field is necessary . In this study, using rainfed olive farming as an experimental model, we determined the stability and accumulation levels of humic substances and appliedthese data to bacterial laccase-encoding gene expression and diversity in soils under four different agricultural management systems (bare soils under tillage/no tillage and vegetation cover under chemical/mechanical management).
Materials and Methods. Humic C (>10 4 Da) was subjected to isoelectric focusing. The GC-MS method was used to analyze aromatic hydrocarbons. Real-Time PCR quantification and denaturing gradient gel electrophoresis ( DGGE) of DNA/RNA for functional bacterial laccase-like multicopper oxidase (LMCO)-encoding genes and transcripts were also carried out.
Results. Soils under spontaneous vegetation, eliminated in springtime using mechanical methods, showed the highest humic acid levels as well as the largest bacterial population, rich in laccase genes and transcripts after more than 30 years of experiments. The structure of the bacterial community based on LMCO genes also pointed to phylogenetic differences between these soils due to the impact of different management systems. Soils where herbicides were used to eliminate spontaneous vegetation once a year and those where pre-emergence herbicides resulted in bare soils clustered together for DNA-based DGGEanalysis, which indicated a certain amount of microbial selection due to the application of herbicides. When LMCO-encoding gene expression was studied, soils where cover vegetation was managed either with herbicides or with mechanical methods showed less than 10% similarity, suggesting that the different laccase substrates derived from vegetation cover decay when herbicides are used.
Conclusions. We suggest that the low humic acid content retrieved in the herbicide-treated soils was mainly related to the type (due to vegetal cover specialization ) and smaller quantity (due to lower vegetal biomass levels) of phenolic substrates for laccase enzymes involved in humification processes. We also found that spontaneous vegetal cover managed using mechanical methods could be the best option for achieving C stabilization in rainfed Mediterranean agroecosystems.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Mass spectra of the mixture of aromatic hydrocarbons (m/z=265+266+331)
Mass spectra of the mixture of aromatic hydrocarbons (m/z=265+266+331)
Raw data
Checking the homology of Cu1AF-Cu2R primers to anneal and amplify the target DNA
DGGE bands
Computer-generated DGGE image used by the UVItec Gel Documentation software for analysing the bands