Elevated atmospheric CO2 increases aboveground plant growth and productivity. However, carbon dioxide-induced alterations in plant growth are also likely to affect belowground processes, including the composition of soil biota. We investigated the influence of increased atmospheric CO2 on bacterial numbers and activity, and on soil microbial community composition in a pasture ecosystem under Free-Air Carbon Dioxide Enrichment (FACE). Composition of the soil microbial communities, in rhizosphere and bulk soil, under two atmospheric CO2 levels was evaluated by using phospholipid fatty acid analysis (PLFA), and total and respiring bacteria counts were determined by epifluorescence microscopy. While populations increased with elevated atmospheric CO2 in bulk soil of white clover (Trifolium repens L.), a higher atmospheric CO2 concentration did not affect total or metabolically active bacteria in bulk soil of perennial ryegrass (Lolium perenne L.). There was no effect of atmospheric CO2 on total bacteria populations per gram of rhizosphere soil. The combined effect of elevated CO2 on total root length of each species and the bacterial population in these rhizospheres, however, resulted in an 85% increase in total rhizosphere bacteria and a 170% increase in respiring rhizosphere bacteria for the two plant species, when assessed on a per unit land area basis. Differences in microbial community composition between rhizosphere and bulk soil were evident in samples from white clover, and these communities changed in response to CO2 enrichment. Results of this study indicate that changes in soil microbial activity, numbers, and community composition are likely to occur under elevated atmospheric CO2, but the extent of those changes depend on plant species and the distance that microbes are from the immediate vicinity of the plant root surface.
Bibliographical noteFunding Information:
This research was supported in part by a grant from Natural Sciences and Engineering Research Council (Canada) and by a grant from the University of Minnesota Agricultural Experiment Station (to Mike Sadowsky). We thank Ueli Hartwig and Joe Nösberger for use of the Swiss FACE facility, Urs Zimmerman for providing root data, Jürg Blumenthal for his valuable help and comments on the manuscript, and Nir Shapir for help with graphics.
Copyright 2008 Elsevier B.V., All rights reserved.
- Bulk soil
- Elevated atmospheric CO
- Microbial activity
- Microbial communities
- Phospholipid fatty acids
- Rhizosphere soil