Freeman et al. 2009

Freeman KR, Pescador MY, Reed SC, Costello EK, Robeson MS, Schmidt SK. 2009. Soil CO2 flux and photoautotrophic community composition in high-elevation, ‘barren’ soil. Environmental Microbiology 11: 674-686.

These authors measured photosynthetic carbon fixation and microbial community composition in sub-nival barren soils in the Colorado Front Range of the United States, at 40ºN latitude and approximately 3600m altitude. Like polar desert soils, these sub-nival soils lack conspicuous macrophytic vegetation (vascular plants and bryophytes) and are snow-covered for most of the year. Previous examinations of these systems had suggested the majority of carbon input to these soils was derived from wind-blown dust, but this study demonstrated a much larger input of carbon from in-situ photosynthesis.

Net carbon fixation was estimated by subtracting in-light measurements from in-dark measurements of CO2 flux. All measurements were made using an IRGA system with a 1.18L transparent chamber; dark measurements were made by covering the chamber with a dark, opaque cloth. After measurement of CO2 flux, one site was carefully dug up and transported to the laboratory for molecular-phylogenetic analysis.

The soil was divided into 2 depths: 0-2cm and 2-4cm, then DNA was extracted and PCR using universal bacterial primers for the 16s region was carried out, followed by sequencing. This generated more than 1000 sequences, in 4 bacterial divisions containing known photoautotrophic microorganisms, plus some sequences from eukaryotic green algae.

The most intriguing group of bacteria found were the Chloroflexi, an understudied group found in both depth layers. The taxa composition found in the deeper layer was highly different from the community found in the surface, light-receiving zone, and the authors suggest, based on a few studies done of Chloroflexi in hot-springs environments, that this group may use longer-wavelength light which penetrates deeper in soils. These authors do not make it, but this suggests to me the microphotoautotrophs in this system may be partitioning their environment in both space (depth) and spectrum (red).

This paper includes a large number of references and introductory descriptions for techniques and findings I will need to incorporate into the planning stages (at least) of my future studies in the polar desert. In particular, the molecular approach to the phylogenetics and biodiversity of the soil photoautotrophs seems both powerful and relatively uncomplicated. There are many procedures to carry out, to be sure, but the justification for each is clear, and the sequence of operations appears to be linear.