Abstract for presentation at Biodiversity Extinction Crisis Conference - A Pacific Response

Organic carbon in arable soils continues to decline. The movement of carbon from soil adds to the most common greenhouse gas held in the atmosphere. Thus measures to reduce or reverse losses of carbon from soil will assist global measures to manage a threatening process. Photosynthesis is the source of all carbon entering soil. However, most plant materials degrade rapidly.
We have examined the microbial contribution to carbon stored in arable soils: via arbuscular mycorrhizal (AM) and saprotrophic fungi. In microcosms where the effects of AM fungi were separated from those of roots, seedlings were grown with AM fungi for 12 months. Soils containing AM fungi and AM fungi plus roots contained significantly more organic carbon than soils containing roots, or neither roots or AM fungi. Similarly, a few isolates of saprotrophic fungi in the Trichocomaceae when grown with exogenous carbon in sterile soil increased organic matter held in the soil matrix. Increased carbon was not necessarily associated with increased soil aggregation, or with increased fungal biomass. While the research is ongoing, the mechanisms for carbon increase appear to be associated with either or both the release of recalcitrant carbon or the transformation of carbon to more resilient forms by the fungi.
As management of plant resources in arable systems has resulted in only minor changes to levels of organic carbon stored in arable soils, closer examination of the contribution of soil microbes may result in increased carbon sequestration in the field. Microbes have previously received little recognition for their importance in local or global environmental issues. Measures to document diversity and functional attributes of these organisms are urgently needed.