The rhizosphere microbiome of burned holm-oak: potential role of the genus Arthrobacter in the recovery of burned soils

Study Extent

The study area is located in the Sierra Nevada Natural and National Park (SE Spain), where a wildfire in September 2005 burned 3426.74 ha, including 412 ha of evergreen holm oaks (Q. ilex subsp. ballota). Soil samples were collected in the valley of the Lanjarón River where two sites were selected: one in an area directly affected by the wildfire (burned forest containing holm oak trees [BOF]) and a nearby site in evergreen, undisturbed oak forest (UOF)

Sampling

Three sampling plots were randomly chosen within each study site along transects of 1.0 km length. At the BOF and UOF sites, we sampled the rhizosphere of three trees per plot, each with a diameter of at least 15 cm at breast height and separated by at least 5 m. Sampling took place on April 29, 2008 (3 years after the wildfire). Both sites were on a south-facing steep slope. The rhizospheric samples were collected from from holm oak rhizosphere soils by following the tree’s main roots until young cork-free roots were found at a distance of less than 50 cm from the trunk. The soil attached to the roots was manually removed and the roots with rhizospheric soil were put into 50 ml Falcon tubes filled with 20 ml of sterilized NaCl 0.8%. After shaking 25 min at 150 rpm and room temperature, the roots were removed and the tubes were centrifuged at 12,850 g for 5 min. The pelleted soil was used to extract environmental DNA. On the other hand, we processed up to 2 kg of soil from each site, sieved through a 2 mm mesh, for physicochemical analysis including soil type, pH, available water, total nitrogen, organic matter, electrical conductivity, etc. All these analyses were carried out with standardized procedures at the Food and Agriculture Laboratory of the Andalusian regional government at Atarfe (Granada, Spain).

Quality Control

In each treatment, 3 healthy trees were taken in 3 independent plots, with more than 1km distance between them to have a representative sample of each site. The DNA from the 3 trees in the same plot was mixed before sequencing to obtain a homogeneous composite sample from each plot. Finally, 3 composite replicates were obtained from each site, BOF as a burn treatment and UOF as a control treatment.

Method steps

1. The methodological steps were publised in detail in the paper entitled: The rhizosphere microbiome of burned holm-oak: potential role of the genus Arthrobacter in the recovery of burned soils. With DOI: https://doi.org/10.1038/s41598-017-06112-3

1. Bacteria
   common name: Bacteria rank: domain
2. Archaea
   common name: Archaea rank: domain

The soil samples were collected from Lanjarón, Sierra Nevada, Granada, Spain Undisturbed holm oak forest rhizosphere were collected at 1790 meters above sea level. Burned holm oak forest rhizosphere were collected at 1566 meters above sea level.