Metagenomic Assessment of the Potential Microbial Nitrogen Pathways in the Rhizosphere of a Mediterranean Forest After a Wildfire
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Wildfires are frequent in the forests of the Mediterranean Basin and have greatly influenced this ecosystem. Changes to the physical and chemical properties of the soil, due to fire and post-fire conditions, result in alterations of both the bacterial communities and the nitrogen cycle. We explored the effects of a holm oak forest wildfire on the rhizospheric bacterial communities involved in the nitrogen cycle. Metagenomic data of the genes involved in the nitrogen cycle showed that both the undisturbed and burned rhizospheres had a conservative nitrogen cycle with a larger number of sequences related to the nitrogen incorporation pathways and a lower number for nitrogen output. However, the burned rhizosphere showed a statistically significant increase in the number of sequences for nitrogen incorporation (allantoin utilization and nitrogen fixation) and a significantly lower number of sequences for denitrification and dissimilatory nitrite reductase subsystems, possibly in order to compensate for nitrogen loss from the soil after burning. The genetic potential for nitrogen incorporation into the ecosystem was assessed through the diversity of the nitrogenase reductase enzyme, which is encoded by the nifH gene. We found that nifH gene diversity and richness were lower in burned than in undisturbed rhizospheric soils. The structure of the bacterial communities involved in the nitrogen cycle showed a statistically significant increase of Actinobacteria and Firmicutes phyla after the wildfire. Both approaches showed the important role of gram-positive bacteria in the ecosystem after a wildfire.
KeywordsMetagenomics Microbial communities Nitrogen cycle Rhizosphere Wildfire Mediterranean forest
We would like to thank the authorities of the Sierra Nevada National Park for the access, facilities, and soil sampling. This work was funded by the following grants: P08-CVI-03549 from the Consejería de Innovación, Ciencia y Empresa of the Junta de Andalucía, OAPN 021/2007 and OAPN 748/2012 from the Organismo Autónomo Parques Nacionales (Ministry of the Environment), including ERDF (European Regional Development Fund). JFCD was awarded a predoctoral fellowship from the Junta de Andalucia, and AJFG was awarded a predoctoral fellowship (FPU) from the Spanish Ministry of Education.
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