Page 208 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 9. Long-term warming effects on permafrost soil microbial communities
Physicochemical pore water and bulk soil properties
Pore water analysis on initial samples indicated clear differences between AL, TL, and PF (Fig. S2). Ammonium concentrations decreased along the depth gradient (2.0, 0.7, and 0.3 mg L-1, respectively). Overall, nitrite was very low (<0.1 mg L-1) and nitrate was negligible (<0.01 mg L-1, not shown). Sulfate contents were highest in AL and TL (2.9 and 3.3 mg L-1) and lowest in PF (1.5 mg L-1). PF was characterized by higher moisture content (80.9%), higher total C (17.7%), and total N (0.54%). Overall, C/N ratios were similar in all layers and they ranged between 29.6% and 32.7%. Ferrous [Fe(II)] iron content in TL was approximately 10-fold higher than in AL and PF (37.5 vs 3.7 and 3.9 mg L-1, respectively). In contrast, Fe(III) contents were higher in AL and PF (11.8 and 8.9 mg L-1) compared to TL (4.9 mg L-1). The pH was slightly acidic for all samples and ranged from 5.4 in AL to 5.5 in TL and 5.6 in PF (Fig. S2)
Taxonomic and functional shifts upon long-term warming
Long-term warming resulted in a pronounced shift in both the taxonomic and functional profile of the microbial community in all layers (Fig. 2). The taxonomic and functional profile in TL and PF were more pronounced than those in AL. The strongest shift in the taxonomic profile was observed in PF, while the functional profile most strongly shifted in TL. Visual inspection based on a procrustes plot highlights lower concordance between the functional and taxonomic compositions for TL and PF than for AL (Fig. S3). Regarding taxonomic shifts, the rpS3-based analysis confirmed the observed changes based on the 16S rRNA gene with some differences in the relative abundances of major microbial groups (Supplementary Document 1). In addition, the qPCR result revealed that the abundance of bacteria and especially of methanogenic archaea overall declined after long-term incubation (Fig. S4).
206