Plant and Soil

, Volume 251, Issue 1, pp 13-21

First online:

Effects of elevated atmospheric CO2 on protozoan abundance in soil planted with wheat and on decomposition of wheat roots

  • Regin RønnAffiliated withDepartment of Terrestrial Ecology, Zoological Institute, University of Copenhagen Email author 
  • , Flemming EkelundAffiliated withDepartment of Terrestrial Ecology, Zoological Institute, University of Copenhagen
  • , Søren ChristensenAffiliated withDepartment of Evolutionary Biology, Zoological Institute, University of Copenhagen

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The effect of elevated CO2 on growth of wheat plants (Triticum aestivum cv. Minaret) and soil protozoan and bacterial populations was investigated in soil pots placed in open top chambers fumigated with ambient air or air enriched with CO2 (ambient + 320 μl L−1 CO2). We harvested plants two times during the growing season and measured the biomass and the C and N content of roots and shoots. The soil was divided into bulk and rhizosphere soil and the number of bacteria (colony-forming units, CFU) and protozoa was determined. There was no effect of atmospheric CO2 content on the number of bacteria, but the total number of bacterivorous protozoa was higher in pots from the elevated CO2 treatment. This increase was mainly due to an increase in the number of protozoa in the bulk soil. Density of protozoa in the rhizosphere was not affected by elevated CO2. This suggests that the increase in protozoan numbers was a result of a general increase in rhizodeposition, presumably caused by increased root production, and not to an increased root exudation per root mass. After harvest, soil from the two treatments was incubated with and without roots and the respiration rate was estimated at intervals for 200 days. During the first 55 days, the specific root induced respiration rate was not affected by the CO2 level at which the plants had been grown, indicating that the quality of the easily decomposable components of the roots was not affected by CO2 level.

bacteria decomposition elevated CO2 rhizosphere soil protozoa wheat roots