Controls on the production, incorporation and decomposition of glomalin - a novel fungal soil protein important to soil carbon

OAK B263 Glomalin is an operationally defined soil protein, produced by arbuscular mycorrhizal fungi (AMF), with importance in soil carbon sequestration through its relationship with soil aggregation. The goal of the project was to further explore the natural history of glomalin and to address several questions regarding basic behavior of this compound in soil (production, incorporation, decomposition). We have obtained a significant amount of novel information on the arbuscular mycorrhizal fungal soil protein, concerning factors controlling its production to mechanisms of incorporation and decomposition. These findings have resulted in 10 publications in peer-reviewed journals, with several more submitted or in preparation, and 16 contributed presentations at meetings. I have sought collaborative opportunities whenever they fit within the research proposed to enhance our productivity. Additionally, although not part of the original proposed work, we have made a significant effort to elucidate the molecular biology of glomalin (in response to Program Officer suggestions). In addition to peer-reviewed publications there have also been a number of invited presentations, including a keynote address delivered by the PI at the International Conference on Mycorrhizae (ICOM4) in Montreal, summer 2003. Two Master's students have been trained (and graduated), and a postdoctoral associate has been mentored, as well as numerous undergraduate researchers at UM. In this report I summarize the major findings of the project in the areas of glomalin production control (host factors, elevated CO2), incorporation, and decomposition. Section D is newly added and describes recent progress in molecular biology. Briefly, we found that glomalin production is influenced by the host, as shown by host species effects and responses to elevated CO2. We have recently made a significant breakthrough in understanding how glomalin may become deposited into soil; apparently the dominant pathway is via hyphal turnover rather than by secretion (as previously assumed). In terms of decomposition, we have learned that glomalin is surprisingly stable (data from soil incubation experiments and from carbon dating) and has a residence time far greater than the AMF hyphae (on the order of decades, putting at least some glomalin fractions in the slow soil C pool). Finally, our exploratory work on molecular biology of glomalin has yielded some promising preliminary data (including an immunoreactive band that was used to obtain N-terminal amino acid sequence). While the gene has not yet been identified, this strongly suggests that glomalin is a unique compound; - a significant step from an operational definition (based on soil extraction conditions) to biochemical characterization