Zhou et al. 2008

Zhou J, Kang S, Schadt CW, Garten CT Jr. 2008. Spatial scaling of functional gene diversity across various microbial taxa. Proceedings of the National Academy of Sciences of the USA 105: 7768-7773.

These authors used a microarray-based technique to estimate biodiversity of soil microbes across a pair of transects in a forest in Tennessee. Their analysis found rates of species turnover through space much lower than rates for macroorganisms such as “higher” plants and animals.

The species-area relationship, generalized to the Taxa-Area-Relationship (TAR), is S=cA^z, where S is the number of species, A is the area, c is the intercept in log-log space, and z is a measure of the rate of species turnover across space. Values of z for macroorganisms have been estimated close the theoretically derived value of 0.25, while previous estimates for microbes have been often much lower, but occasionally much higher. This study found a range of z-values, all a bit less than 0.1.

The key technique used in this study was the GeoChip, a microarray with nearly 25000 50-mer probes for more than 10000 genes in functional groups such as denitrification or heavy-metal resistance. As such, it represents an excellent tool for such investigations, because it reduces or avoids many of the microbe-diversity sampling artifacts such as undersampling that plague other methods.

A large fraction of the observed variation in sequences across the transects was unexplained. These authors speculate that a fraction of this unexplained variation may be driven by unexamined patterns and processes including biotic interactions (competition, trophic interaction), abiotic interactions (O2 concentrations, labile C pool), and microscale effects below 1m scales.

One interesting suggestion by these authors is to use metagenomic approaches to characterize key sequences of interest in a particular system, and then examine biodiversity using a microarray customized for these sequences. This is in line with what I was thinking in regards to using such techniques in polar desert soils – first, characterize what is there; second, look at biodiversity and patterns within diversity relating to groups of interest.