Short-Term Response of Soil Bacterial Communities after Prescribed Fires in Semi-Arid Mediterranean Forests

Abstract

Low-intensity burnings could be an effective silvicultural tool to prevent the occurrence and severity of wildfires. Nevertheless, their use as a forest fuel reduction tool may have a negative impact on soil properties. The aim of this investigation was to study the impact of a low-intensity prescribed fire on the main chemical properties of the soil (pH, electrical conductivity, and total organic carbon), and the diversity and composition of the soil bacterial communities in a semi-arid forest in SE Spain. Two similar stands were treated with a low-intensity prescribed burn in spring and autumn 2018 and were compared to an unburned stand. All soil samples were collected at the same time (autumn 2018). The chemical properties of the soil showed no significant differences between the prescribed burns and the control forest. Shannon and Pielou’s diversity indices presented values significantly lower in the burned soils compared to the control. Prescribed burning did not modify soil bacterial community structure at the phylum level, but NMDS analysis did reveal a difference between soil bacterial communities at the genus level. Both prescribed burnings favoured some bacterial taxa over others, suggesting different thermal and bacterial resistance. The presence of Massilia, Pseudomonas and Arthrobacter could suggest a short-term ecosystem recovery. Therefore, prescribed burning in semi-arid forests could be suitable as a preventive tool against wildfires.

Combined Use of a Bacterial Consortium and Early-Colonizing Plants as a Treatment for Soil Recovery after Fire: A Model Based on Los Guájares (Granada, Spain) Wildfire

“…However, higher intensity levels require a time frame that could be too late for soil recovery. Soria et al also focused on the Mediterranean region, and this initial loss of general diversity is reflected, but an increase in some genera such as Pseudomonas has been reported, which is also observed in our studies [91]. However, our work, although limited to the cultivable portion of the population, found that the predominant genera in these soils were Peribacillus or Bacillus, as is also reflected in the studies by Matos et al [92].…”

A granular view of the traits controlling soil bacterial community reconstruction following a prescribed burn

“…Recapitulating previous results, we identified MAGs related to taxa which are known to be fire responsive across diverse ecosystems including those belonging to genus Arthrobacter (n=5, including genera Arthrobacter_F and Arthrobacter_H as classified by GTDB-Tk) 10,14,15,18,26,27 , Blastococcus (n=1) 10,15,23,26 and Telluria (n=2, formerly Massilia 28 ) 14,15,18,23,26 . We also identified other previously reported fire responsive taxa including Aeromicrobium 15,23 and Pseudomonas_E 17 , but not all MAGs belonging to those genera were found to be enriched in burned vs. unburned (Fig 5). Our findings add an even more divergent ecosystem (grassland) and fire regime (low-severity prescribed fire) to the growing list of systems in which these taxa have emerged as pyrophilous, while the genetic information in the MAGs informs our emerging understanding of bacterial fire ecology.…”

“…Therefore, not only are post-fire microbiomes potentially simpler to characterize, but successive timepoints and non-burned controls provide an opportunity to observe the enrichment of specific species after burns. Several genetic traits have been implicated in microbial fire-response through changes in microbiome composition detected through 16S rRNA amplicon sequencing [14][15][16][17][18] , such as ability to form spores, ability to degrade pyrogenic organic matter or fast growth potential to take advantage of the reduced competition immediately after fire. However, there remains a need to more directly connect genetic traits with success post-fire through both genome-resolved methods and controlled assessment of different timepoints.…”