Wagner et al. 2009

Wagner D, Kobabe S, Liebner S. 2009. Bacterial community structure and carbon turnover in permafrost-affected soils of the Lena Delta, northeastern Siberia. Canadian Journal of Microbiology 55: 73-83.

These authors examined the microbial communities at two depth bands (near-surface and near-permafrost) in low-centred tundra polygons at the vast permafrost wetland of the delta of the Lena River. The delta covers more than 60 000 km^2, and much of it appears to be a reserve or national park of Russia. The CAVM (Walker et al. 2002) describes most of the delta as vegetation type W2, sedge, moss, dwarf-shrub wetland, and satellite images from Google maps shows very extensive lake and pond coverage of the landscape. In short, it’s pretty wet, and generally cold.

The general finding of this paper is that while near-surface communities include a wide diversity of aerobic and facultatively-anaerobic bacteria, the deeper, colder, anaerobic portions of the soil contain almost no aerobes, and are instead dominated by “fermenting” species capable of decomposing recalcitrant organic carbon molecules under negative-redox conditions. There is a sharp temperature gradient, which combined with the poorer quality of carbon, the lack of oxygen and negative redox conditions, and the general water saturation at depth creates conditions near the permafrost suitable only for the slow microbial metabolisms. None of this is particularly surprising, but the observation of decreased biodiversity with water saturation does suggest the worrying possibility that increased water in this system, driven by melting permafrost and climate change (particularly upstream in the long and North-flowing Lena) could drive these microbial communities to lose some “physiological skills” such as the ability to oxidize methane, a metabolic pathway possessed only by some aerobic prokaryotes.

This paper is quite important to my own work, I think. Besides emphasizing the role of water content in structuring soil chemical and especially biological conditions, the description of the methods used to measure microbial biodiversity should be useful. However, while the BIOLOG plates seem interesting, the results of this technique are not at all well explained in this paper. I do not know what is indicated by the relationship shown in Figure 3, for example, of changes in colour development associated with carbon turnover of various categories of organic substrates. Several of the figures are simple plots of principal component analysis (PCA), literally just PC1 vs. PC2 with some outlines drawn around some clusters. I’m sure there is more of interest in this paper besides the coarse outline of biodiversity differences in communities, but without a more thorough explanation of the nearly-raw data I cannot see it.