ena-STUDY-MSUCME-06-06-2013-00:10:11:896-192
Differences in nifH- Diversity and Associated Taxa Across an Alaskan Permafrost Thaw Gradient
Since nitrogen (N) is often limiting in permafrost soils, we investigated the N2-fixing genetic potential and the inferred taxa harboring those genes by sequencing nifH gene fragments in samples taken along a permafrost thaw gradient in an Alaskan boreal soil. Samples from minimally, moderately and extensively thawed sites were taken to a depth of 79 cm to encompass zones above and below current thaw depths. NifH reads were translated with frameshift correction and 112,476 sequences were clustered at 5% amino acid dissimilarity resulting in 1,631 OTUs.  Representative sequences of each cluster linked to the nearest neighbor produced 123 unique reference database matches. Sample depth in relation to thaw depth rather than extent of thaw showed differences in the NifH sequence classes. NifH sequences most closely related to group I nifH-harboring Alpha- and Beta Proteobacteria were in higher abundance above thaw depth while those related to group III nifH-harboring Delta Proteobacteria were more abundant below thaw depth. Overall, these results suggest that permafrost thawing will result in changes in the class-level composition of N2-fixing communities in the thawed soil layers. These nifH data were also compared to nifH sequences obtained from a previous study at an Alaskan taiga site, and to those of other geographically distant, non-permafrost sites. The two AK sites were differentiated largely by changes in relative abundances of the same OTUs, whereas the non-Alaska sites were differentiated by the lack of many Alaskan OTUs, and the presence of unique halophilic, sulfate- and iron-reducing taxa in the Alaska sites.
Since nitrogen (N) is often limiting in permafrost soils, we investigated the N2-fixing genetic potential and the inferred taxa harboring those genes by sequencing nifH gene fragments in samples taken along a permafrost thaw gradient in an Alaskan boreal soil. Samples from minimally, moderately and extensively thawed sites were taken to a depth of 79 cm to encompass zones above and below current thaw depths. NifH reads were translated with frameshift correction and 112,476 sequences were clustered at 5% amino acid dissimilarity resulting in 1,631 OTUs.  Representative sequences of each cluster linked to the nearest neighbor produced 123 unique reference database matches. Sample depth in relation to thaw depth rather than extent of thaw showed differences in the NifH sequence classes. NifH sequences most closely related to group I nifH-harboring Alpha- and Beta Proteobacteria were in higher abundance above thaw depth while those related to group III nifH-harboring Delta Proteobacteria were more abundant below thaw depth. Overall, these results suggest that permafrost thawing will result in changes in the class-level composition of N2-fixing communities in the thawed soil layers. These nifH data were also compared to nifH sequences obtained from a previous study at an Alaskan taiga site, and to those of other geographically distant, non-permafrost sites. The two AK sites were differentiated largely by changes in relative abundances of the same OTUs, whereas the non-Alaska sites were differentiated by the lack of many Alaskan OTUs, and the presence of unique halophilic, sulfate- and iron-reducing taxa in the Alaska sites.