Reference
Insam, H., Baath, E., Berreck, M., Frostegard, A., Gerzabek, M.H., Kraft, A., Schinner, F., Schweiger, P. and Tschuggnall, G. 1999. Responses of the soil microbiota to elevated CO2 in an artificial tropical ecosystem. Journal of Microbiological Methods 36: 45-54.
What was done
The authors constructed artificial tropical ecosystems, each composed of 77 plants representing seven C3 species, upon nutrient-poor soils and subjected them to atmospheric CO2 concentrations of 340 and 610 ppm for 530 days to study the effects of elevated CO2 on plant growth and soil microbiota.
What was learned
Although elevated CO2 did not significantly affect the total soil organic carbon in these experimental ecosystems, it did increase the presence of soil humic substances by almost 30%. Additionally, atmospheric CO2 enrichment did not increase the total percentage of root length colonized by mycorrhizal fungi, but it did support greater numbers of mycorrhizal fungi due to its enhancement of plant root lengths. Finally, elevated CO2 was found to have no significant impact on microbial community composition, even after nearly 1.5 years of atmospheric CO2 enrichment.
What it means
As the CO2 content of the air continues to rise, it is likely that tropical soils may contain greater proportions of their organic carbon pools as humic substances, which not only increase soil water holding capacity, nutrient composition, and stability, but decay relatively slowly, thus sequestering soil carbon for longer periods of time. In addition, with more CO2 in the atmosphere, it is likely that enhanced mycorrhizal networks will result from greater fungal populations colonizing plant roots. Both of these phenomena should allow plants to grow more robustly in response to the rising CO2 content of the air.
At another level, the results of this study suggest that the air's rising CO2 content will maintain soil bacterial biodiversity, while significantly increasing bacterial numbers. Therefore, increased bacterial numbers will likely result in greater overall soil bacterial processes, including those which make important soil minerals readily available for plant usage. Thus, this phenomenon, too, should allow plants to grow even better in response to the aerial fertilization effect brought about by increasing atmospheric CO2 concentrations.
Reviewed 1 April 2000