Microbial recolonization and chemical changes in a soil heated at different temperatures

Abstract

Samples of a Mediterranean forest soil were exposed in a muffle furnace to seven temperatures (100–700°C) for 15 min to simulate different fire intensities. Heated soils were incubated for 100 days after re-inoculation with fresh unheated soil. Immediately after heating, the extractable organic C increased with the heating temperature, reaching a maximum at 400°C. This increase in extractable organic C and nutrients in soils heated below 400°C allowed a rapid recolonization of bacteria, increasing the basal respiration. During the 100-day incubation, the cumulative values of basal respiration and carbon mineralization rates generally followed a double exponential equation in unheated and heated samples. Heating at 200°C caused a reduction of 99.6% for fungi (measured as culturable fungal propagules), which showed lower recolonization capacity than that of bacteria. Heating also caused a decrease in the organic C content of the soils, especially for the highest temperatures. As a consequence, the microbial biomass carbon recovery was short lived in heated soils. The varied effects of heating and incubation on the inorganic and organic nitrogen changes, available nutrients and metabolic quotients are also discussed. This study demonstrates that changes in soils exposed to comparatively high temperatures (>500°C) have a particularly strong impact on microbial population.

Long-distance dispersal and recolonization of a fire-destroyed niche by a mite-associated fungus

“…It is, therefore, surprising that this study appears to be the first to consider post-fire recolonization of plant-associated fungi. Investigations into the effect of fire on soil microbial biomass in Mediterranean regions (Dumontet et al, 1996) have revealed that fungi are more susceptible to fire and re-establish less easily than bacteria (Bárcenas-Moreno et al, 2011;Guerrero et al, 2005). The niche space availability and elimination of competition provided by fire, however, apparently facilitates rapid re-establishment.…”

How wildfires affect soil properties. A brief review

“…Different groups of microorganisms show different strategies against disturbances. Fungi, for example, often show greater resistance than bacteria (Dunn et al, 1985), although bacteria can recover faster (Guerrero et al, 2000;Guerrero et al, 2005;Bárcenas-Moreno and Baath, 2009;Ponder et al, 2009;Bárcenas-Moreno et al, 2011). However, if fire intensity is sufficiently high, soil may become partially sterilized (Pietikäinen and Fritze, 1995).…”

Index for Characterizing Post-Fire Soil Environments in Temperate Coniferous Forests

“…Plant-available ammonium and nitrate can increase concomitantly with temperature and duration until they begin to volatilize [4,5], which most likely occurs on sites containing black-colored soils (PFI categories 2.1-2.3 and 3.1-3.3). As organic carbon is volatilized, concentrations of inorganic compounds such as potassium increase, although little change occurs with calcium [93]. Thus, in PFI categories 3.3 and 3.4 or 4.3 and 4.4 with gray or orange colored soils [6,47] several inorganic elements would be abundant.…”

“…If gray ash is abundant and there is little to no surface organic layer remaining, a large portion of the total nitrogen may be absent (PFI category 4.3) [4]. However, if there is an abundance of surface organic material (PFI categories 1.0 and 2.0), and no gray-or orange-colored soils, [6,45,46], temperatures were insufficient to volatilize all the nitrogen [93]. Plant-available ammonium and nitrate can increase concomitantly with temperature and duration until they begin to volatilize [4,5], which most likely occurs on sites containing black-colored soils (PFI categories 2.1-2.3 and 3.1-3.3).…”

“…Harvey et al [41] reported that in some forests up to 56% of the nitrogen occurs within the forest floor, surface mineral soil, and woody residue. During a fire, these components are vulnerable to loss through consumption and soil heating [93]. If gray ash is abundant and there is little to no surface organic layer remaining, a large portion of the total nitrogen may be absent (PFI category 4.3) [4].…”