Roots, Mycorrhizae and Soil Respiration
By growing the rmc and 76R MYC+ tomato genotypes, with their near matched biomass, in an automated respiration monitoring system, we were able to study the mycorrhrizal contribution to soil respiration with a high degree of resolution. While roots contributed significantly to soil respiration, total CO2 respired did not differ between the rmc and 76R MYC+ genotypes. However, AMF appear to have contributed to soil respiration as root length density was higher in the rmc treatment. Although colonization of roots by AMF may not have had an effect on total respiration, it may have altered the source partitioning of respiration. Thus, the contribution of AMF to soil respiration should not be overlooked. The use of these two genotypes avoided any indirect effects of establishment of non-mycorrhizal controls on the wider soil biota, which in turn may lead to a decrease in their abundance and/or activity, and hence over estimation of heterotrophic respiration. Finally, while it is currently not technically possible to separate out the root and AMF contributions to soil respiration on a whole plant scale, this research suggests that AMF may have a small role in belowground respiration in tomato.
Cavagnaro, T.R., J.A. Langley, L.E. Jackson, S.M. Smukler, and G.W. Koch. 2008. Growth, nutrition, and soil respiration of a mycorrhiza-defective tomato mutant and its mycorrhizal wild-type progenitor. Functional Plant Ecology 35:228-225.