Dynamics of soil aggregation as affected by land use in grasslands and forests

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An important ecosystem process in grasslands and forests is the dynamic process of soil aggregation. Though often assessed as a static phenomenon, soil aggregates are constantly formed and degraded. Soils sequestering large amounts of C demonstrate regular turnover of aggregates, but we have found that some common grassland land uses lead to remarkably stable soils. This stability appears to be due, at least in part, to hyphal networks of arbuscular mycorrhizal fungi (AMF). Soil structure in forests is less well studied, and is less likely to be affected by AMF, which occur at lower levels in forests than in grasslands. Thus, ectomycorrhizal and saprophytic fungi are expected to be more important for soil aggregation in forest soils. Our overall hypothesis is that as land use intensity increases total aggregation will decrease, along with increased turnover of macroaggregates and decreased formation of microaggregates. We will use hyphal in-growth cores in the field (grassland and forest) to isolate fungal effects on aggregation dynamics, and in the greenhouse to separate effects of AMF, non-AMF, and bacteria. The project focuses on how functional diversity of soil fungi, defined here as ability to aggregate soils, is affected by land use. We expect the outcome of this project to provide novel information on how land-use intensity affects dynamics of soil aggregation, and on how those dynamics are influenced by interactions between soil microbes.