Burning Fire-Prone Mediterranean Shrublands: Immediate Changes in Soil Microbial Community Structure and Ecosystem Functions

Abstract

Wildfires subject soil microbes to extreme temperatures and modify their physical and chemical habitat. This might immediately alter their community structure and ecosystem functions. We burned a fire-prone shrubland under controlled conditions to investigate (1) the fire-induced changes in the community structure of soil archaea, bacteria and fungi by analysing 16S or 18S rRNA gene amplicons separated through denaturing gradient gel electrophoresis; (2) the physical and chemical variables determining the immediate shifts in the microbial community structure; and (3) the microbial drivers of the change in ecosystem functions related to biogeochemical cycling. Prokaryotes and eukaryotes were structured by the local environment in pre-fire soils. Fire caused a significant shift in the microbial community structure, biomass C, respiration and soil hydrolases. One-day changes in bacterial and fungal community structure correlated to the rise in total organic C and NO(3)(-)-N caused by the combustion of plant residues. In the following week, bacterial communities shifted further forced by desiccation and increasing concentrations of macronutrients. Shifts in archaeal community structure were unrelated to any of the 18 environmental variables measured. Fire-induced changes in the community structure of bacteria, rather than archaea or fungi, were correlated to the enhanced microbial biomass, CO(2) production and hydrolysis of C and P organics. This is the first report on the combined effects of fire on the three biological domains in soils. We concluded that immediately after fire the biogeochemical cycling in Mediterranean shrublands becomes less conservative through the increased microbial biomass, activity and changes in the bacterial community structure.

Wildfire effects on the properties and microbial community structure of organic horizon soils in the New Jersey Pinelands

“…Other studies have reported similar trends in a laboratory heating experiment (Hatten and Zabowski, 2009), an experimental fire in Mediterranean shrublands (Goberna et al, 2012), a prescribed fire in a wooded-shrubland in Nevada, USA (Chief et al, 2012), and a ponderosa pine/Douglas fir wildfire in Colorado, USA (Ferrenberg et al, 2013). Our results also showed that the decreases in GWC, OM, and TKN in the organic horizon soils persisted up to 25 months post-fire, suggesting that the recovery of soil physical and chemical properties after a wildfire may be slow.…”

“…Several recent studies have shown declines in total soil microbial biomass in the mineral horizon after a fire (Choromanska and DeLuca, 2001;Yeager et al, 2005;Smith et al, 2008;Dooley and Treseder, 2012) while others have reported increases in microbial biomass post-fire (Goberna et al, 2012) or no significant difference in microbial biomass between non-burned and burned soils (Hamman et al, 2007). Similarly bacterial community structure in the mineral horizon has also been shown to be sensitive to fire, as exemplified with an experimental fire in a Mediterranean shrubland, which revealed a shift in bacterial community structure (Goberna et al, 2012). Related studies have revealed bacterial diversity decreases after a wildfire of red pine in Japan (Mabuhay et al, 2006) and after prescribed burning of an upland oak forest in the USA (Williams et al, 2012).…”

“…Jurgens and Saano (1999) showed that Crenarchaeota dominated boreal forests that were subjected to both clear-cutting and prescribed burning. Additionally, archaeal community structure shifted immediately following a prescribed burn in Mediterranean shrublands, correlating with changes in ammonium nitrogen and soil pH (Goberna et al, 2012).…”

Soil gross N transformation rates after a wildfire and straw mulch application for burned soil emergency stabilisation

“…Contrasting results about the effects of fire on ammonia oxidising microorganisms and nitrification have been published. At the short-term, fires have neither effects on nitrifiers (Acea and Carballas 1996) nor on ammonia oxidising archaea (Goberna et al 2012), despite burning that altered the community structure of all archaea, bacteria and fungi, as well as microbial biomass and activity (Barreiro et al 2010;Díaz-Raviña et al 1996;Goberna et al 2012). At the long-term, nitrifier abundance was increased by the fires (Acea and Carballas 1996;Ball et al 2010).…”

Deterministic processes dominate nematode community structure in the Fynbos Mediterranean heathland of South Africa

“…Despite the short terms effects, all these studies found that the influence of fire history on nematode community was undetectable in the long term (Renčo and Č erevková 2015). Similarly, De Marco et al (2005) and (Docherty et al 2012;Goberna et al 2012) found that the effects fire has on soil biochemistry and microbial communities were undetectable 33 months after a fire. There is clearly, then, the possibility of patterns in nematode diversity and community structure that exist beyond the effects of fire, perhaps influenced by underlying habitat and soil factors.…”