Abstract
Wildfires destabilize biocrust, requiring decades for most biological constituents to regenerate, but bacteria may recover quickly and mitigate the detrimental consequences of burnt soils. To evaluate the short-term recovery of biocrust bacteria, we tracked shifts in bacterial community form and function in Cyanobacteria/lichen-dominated (shrub interspaces) and Cyanobacteria/moss-dominated (beneath Artemisia tridentata) biocrusts one week, two months, and one year following a large-scale burn manipulations in a cold desert (Utah, USA). We found no evidence of the burned bacterial community recovering to a burgeoning biocrust. The foundational biocrust phyla, Cyanobacteria, dominated by Microcoleus viginatus (Microcoleaceae), disappeared from burned soils creating communities void of photosynthetic taxa. One year after the fire, the burned biocrust constituents had eroded away and the bare soils supported the formation of a convergent community of chemoheterotrophic copiotrophs regardless of location. The emergent community was dominated by a previouly rare Planococcus species (family Planococcaceae, Firmicutes) and taxa in the Cellulomonadaceae (Actinobacteria), and Oxalobacteraceae (Betaproteobacteria). Previously burnt soils maintained similar levels of bacterial biomass, alpha diversity, and richness as unburned biocrusts, but supported diffuse, poorly-interconnected communities with 75% fewer species interactions. Nitrogen fixation declined at least 3.5-fold in the burnt soils but ammonium concentrations continued to rise through the year, suggesting that the exhaustion of organic C released from the fire, and not N, may diminish the longevity of the emergent community. Our results demonstrate that biocrust bacteria may recover rapidly after burning, albeit along a different community trajectory, as rare bacteria become dominant, species interconnectedness diminishes, and ecosystem services fail to rebound.
Highlights
IntroductionFire may dramatically alter soil bacteria communities depending on the biome being burned (Pressler et al, 2019); fire characteristics [e.g., type (i.e., low-intensity vs. high-intensity, Xiang et al, 2014; Koster et al, 2016) and frequency (e.g., single vs. multiple, Hawkes and Flechtner, 2002; Guenon and Gros, 2013)], and depth of burned soil (Kim et al, 2004)
Fire may dramatically alter soil bacteria communities depending on the biome being burned (Pressler et al, 2019); fire characteristics [e.g., type and frequency], and depth of burned soil (Kim et al, 2004)
None of the Cyanobacteria, cyanolichens, green algal lichens, or mosses that composed the visible portion of unburned communities retained a signature of their biocrust type in ordination space along axis 2 (15.6% of the variation) with Cyanobacteria/lichen- and cyanobacteria/moss-dominated crusts creating unique bacterial communities
Summary
Fire may dramatically alter soil bacteria communities depending on the biome being burned (Pressler et al, 2019); fire characteristics [e.g., type (i.e., low-intensity vs. high-intensity, Xiang et al, 2014; Koster et al, 2016) and frequency (e.g., single vs. multiple, Hawkes and Flechtner, 2002; Guenon and Gros, 2013)], and depth of burned soil (Kim et al, 2004). Biocrusts are autochthonally driven with photosynthate and fixed N2 from Cyanobacteria and organic C from other photosynthetic organisms creating a nutrient-rich zone, the “cyanosphere” (Couradeau et al, 2019; Warren et al, 2019) that supports a relatively high level of bacterial biomass and diversity (Chilton et al, 2018) These “living skins of the desert” occupy soil surfaces in close proximity to fuels (e.g., shrubs and grass litter, woody debris) that readily burn (Hilty et al, 2003; Balch et al, 2013) and biocrust constituents themselves are often desiccated and may burn during fire. The loss of biocrusts to fire may detrimentally alter desert ecosystem form and function
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