Soil Aggregation as Mechanism for Understanding the Roles of Rhizosphere Microorganisms in the Sustainable Usage of Natural Resources.

Global food insecurity and rapidly diminishing water, soil, and energy resources resulting from increases in population numbers and wealth are putting pressure on agroecosystems to efficiently produce the most nutrient dense food while maintaining or enhancing natural resources.  To address these needs, the roles of soil biota in sustainable food, feed, and fiber production systems need to be better understood by doing more than identifying the organisms involved or correlating these organisms with a particularly soil parameter.  Soil aggregation is a widely-impacting soil parameter involved in several soil processes including erosion control, water movement, nutrient cycling, and plant growth and health.  However, two different processes – aggregate formation and aggregate stabilization – are involved in aggregation with often contrary biological, chemical, and physical mechanisms whose relationships are derived primarily from corollary evidence.  Polysaccharides which help to 'glue' aggregates together are not water stable biomolecules and/or are readily decomposed unless present in biofilms while hydrophobic biomolecules add surface stability to aggregates but the repelling forces between these molecules would inhibit structural formation.  Arbuscular mycorrhizal fungi are thought to play key roles in both these processes with fungal hyphae creating the lattice structure upon which aggregates are formed and mycorrhizal biomolecules, such as glomalin, stabilizing aggregates.  The data suggesting the relationship between glomalin and aggregate stability has been corollary, where stability was measured on a sub-sample of aggregates while glomalin was extracted from another sub-sample.  To directly relate glomalin to aggregate stability, a sub-sample of aggregates will be subjected to repeated wet-dry cycles to identify different levels of stability followed by sequential extraction of polysaccharides and glomalin from each group of unstable and stable aggregates.  This data will then be used to begin forming a model for aggregate formation and stability linked to biological activity.