Background
The authors write that biological soil crusts or BSCs "are made of cyanobacteria and other bacterial species, algae, lichens, mosses and microfungi," and that they "cover up to 70% (Belnap and Lange, 2003) of the soil surface of many drylands," which themselves "cover approximately 41% of the Earth's terrestrial surface and support more than one-third of the global population," according to Reynolds et al. (2007). And they note that Elbert et al., (2012) indicate that "the estimated total global carbon net uptake of BSCs has been approximated as 3.9 Pg/year (corresponding to approximately 7% of global net primary production uptake)."

What was done
Working with dynamic gas exchange chambers and cyanobacteria-dominated BSCs taken from the Kalahari Sand soils of southern Africa, Lane et al. quantified short-term changes in carbon exchange (respiration and photosynthesis) of these BSCs when the air's CO2 concentration was doubled to approximately 800 ppm under two different wetting treatments of 2 and 5 mm of applied water, characteristic of "light and heavy rainfall events," respectively.

What was learned
The seven UK scientists report that the BSCs that received 5 mm of wetting increased their rate of carbon sequestration by approximately three-fold, and that those subject to 2 mm of wetting increased their rate of carbon sequestration by a full order of magnitude!

What it means
In the final paragraph of their paper, Lane et al. state that "BSCs have the potential to fix carbon under limited soil moisture availability and nutrient poor soils (typical of drylands)," especially in the case of BSCs dominated by nitrogen fixing cyanobacteria. And, therefore, they conclude that "undisturbed BSC-covered drylands could be enhanced carbon sinks, and play an increasingly significant role in global carbon budgets in years to come."

References
Belnap, J. and Lange, O. 2003. Preface. In: Belnap, J. and Lange, O.L. (Eds.). Biological Soil Crusts: Structure, Function, and Management. Springer-Verlag. Berlin, pp. V-IX.

Elbert, W., Weber, B., Burrows, S., Steinkamp, J., Budel, B., Andreae, M. and Poschl, U. 2012. Contribution of cryptogamic covers to the global cycles of carbon and nitrogen. Nature Geoscience 5: 459-462.

Reynolds, J., Smith, D., Lambin, E., Turner II, B., Mortimore, M., Batterbury, S., Downing, T., Dowlatabadi, H., Fernandez, R., Herrick, F.R., Huber-Sannwald, E., Jiang, H., Leemans, R., Lynam, T., Maestre, F., Ayarza, M. and Walker, B. 2007. Global desertification: building a science for dryland development. Science 316: 847-851.