11/01/2012

Impacts of Elevated CO2 on Photosynthetic Microbes in Arid Ecosystems

Summary

In many harsh desert environments, microbial “biocrust” communities dominated by photosynthetic bacterial species (cyanobacteria) cover up to 70% of the land surface and play important roles in nutrient cycling, water retention, and stabilizing soil against erosion. These communities are highly adapted to the specific environmental conditions of arid ecosystems, and it is unclear what impacts climate change processes may have on them. Operating in collaboration with DOE’s long-term Free-Air CO₂ Enrichment (FACE) program, researchers at Los Alamos National Laboratory have published new findings on the effects of 10 years of controlled elevated CO₂ exposure on cyanobacterial biocrusts using environmental metagenomics. Natural biocrusts exposed to elevated CO₂ (550 ppmv) were shown to have significantly reduced abundance of cyanobacteria relative to plots exposed to ambient CO₂ concentrations (360 ppmv). These findings were correlated with an observed loss of biocrust coverage in the elevated CO₂ plots, although curiously, total soil biomass measurements did not change significantly. Loss of cyanobacterial abundance appears to be at partially related to increased damage from oxidative stress, with genes involved in resistance to this kind of stress appearing more frequently in the elevated CO₂ samples. Although more study is needed, these results present preliminary evidence suggesting that increasing atmospheric CO₂ concentrations have a deleterious impact on desert biocrusts and may result in decreased performance by these communities.

References

Steven, B., L. Gallegos-Graves, C. M. Yeager, J. Belnap, R. D. Evans, and C. R. Kuske. 2012. “Dryland Biological Soil Crust Cyanobacteria Show Unexpected Decreases in Abundance Under Long-Term Elevated CO₂,” Environmental Microbiology, DOI: 10.1111/1462-2920.12011.