Impact of fire on active layer and permafrost microbial communities and metagenomes in an upland Alaskan boreal forest - PubMed (original) (raw)

Impact of fire on active layer and permafrost microbial communities and metagenomes in an upland Alaskan boreal forest

Neslihan Taş et al. ISME J. 2014 Sep.

Abstract

Permafrost soils are large reservoirs of potentially labile carbon (C). Understanding the dynamics of C release from these soils requires us to account for the impact of wildfires, which are increasing in frequency as the climate changes. Boreal wildfires contribute to global emission of greenhouse gases (GHG-CO2, CH4 and N2O) and indirectly result in the thawing of near-surface permafrost. In this study, we aimed to define the impact of fire on soil microbial communities and metabolic potential for GHG fluxes in samples collected up to 1 m depth from an upland black spruce forest near Nome Creek, Alaska. We measured geochemistry, GHG fluxes, potential soil enzyme activities and microbial community structure via 16SrRNA gene and metagenome sequencing. We found that soil moisture, C content and the potential for respiration were reduced by fire, as were microbial community diversity and metabolic potential. There were shifts in dominance of several microbial community members, including a higher abundance of candidate phylum AD3 after fire. The metagenome data showed that fire had a pervasive impact on genes involved in carbohydrate metabolism, methanogenesis and the nitrogen cycle. Although fire resulted in an immediate release of CO2 from surface soils, our results suggest that the potential for emission of GHG was ultimately reduced at all soil depths over the longer term. Because of the size of the permafrost C reservoir, these results are crucial for understanding whether fire produces a positive or negative feedback loop contributing to the global C cycle.

PubMed Disclaimer

Figures

Figure 1

Figure 1

(a) Photos showing the intact and thawed permafrost soils of Nome Creek. Tick marks correspond to 10 cm intervals. (b) CO2 fluxes in the headspace of 8-week long laboratory incubation of samples from control and burned locations. Values are means±s.e. (c) Changes in the extracellular enzyme activities between control and burned locations.

Figure 2

Figure 2

16S rRNA gene sequencing with HiSeq2000 reveal the differences in prokaryotic diversity of samples from control and fire-impacted locations. (a) Communities clustered using principal coordinates analysis of the weighted UniFrac distance matrix. Each point corresponds to a sample colored in red/orange (○) for fire-impacted locations and in blue (◊) for the control locations. Lighter colors present the mineral soil depths. The percentage of variation explained by the plotted principal coordinates is indicated on the axes. (b) Contribution depth, fire and soil geochemistry on observed β-diversity was calculated via variation partitioning and represented as a Venn diagram. (c) Significant contributions of soil geochemistry to observed differences in prokaryotic diversity was tested using ANOVA.

Figure 3

Figure 3

(a) Distribution of phylogenetic groups in the control and burned locations in each soil depth. (b) Pearson's correlation tests were used to detect significant positive or negative correlations (yellow shading) of each phylum to the fire event or soil depth.

Figure 4

Figure 4

(a) Heatmap of intersections in Nome Creek metagenomes. Similarity matrix resulting from the comparison of 11 samples using Compareads (khmer=33, _t_=2, 5.7E7 reads). Gray levels correspond to similarity levels. The three main groups, in blue, turquoise-blue and red, correspond, respectively, to control surface layer (S), control middle (M) and permafrost (D) and all layers from fire-impacted locations. Legend shows the fraction of similarity between the comparisons. (b) Between-class analysis, which visualizes results from PCA and clustering of the KO annotations from 12 metagenomes. The between-class analysis finds the principal components based on the center of gravity of each group as a result every symbol represent two replicate metagenomes. Two principal components are plotted using the ade4 package in R where (◊) surface, (Δ) middle and (○) permafrost (deep soil) layers. Blue color indicates control samples, whereas red indicates fire-impacted samples.

Figure 5

Figure 5

Heat maps indicating differences in relative abundances of functional genes involved in carbon and nitrogen cycle in the Nome Creek metagenomes. Impact of the fire and sampling depth on the observed variation of the relative gene abundances was tested ANOVA analysis, where significant (P<0.05) factors are represented within parentheses.

References

    1. Allison SD, McGuire KL, Treseder KK. Resistance of microbial and soil properties to warming treatment seven years after boreal fire. Soil Biol Biochem. 2010;42:1872–1878.
    1. Baldock JA, Oades JM, Nelson PN, Skene TM, Golchin A, Clarke P. Assessing the extent of decomposition of natural organic materials using solid-state 13C-NMR spectroscopy. Soil Res. 1997;35:1061–1084.
    1. Baldock JA, Masiello CA, Gélinas Y, Hedges JI. Cycling and composition of organic matter in terrestrial and marine ecosystems. Mar Chem. 2004;92:39–64.
    1. Bergner B, Johnstone J, Treseder KK. Experimental warming and burn severity alter soil CO2 flux and soil functional groups in a recently burned boreal forest. Global Change Biol. 2004;10:1996–2004.
    1. Berhe AA, Suttle KB, Burton SD, Banfield JF. Contingency in the direction and mechanics of soil organic matter responses to increased rainfall. Plant Soil. 2012;358:371–383.

Publication types

MeSH terms

Substances

LinkOut - more resources