Defining Functional Soil Metabolic Heterogeneity.

The complex physical structure of soils results in an abundance of anaerobic microsites and associated metabolic gradients even within seemingly aerobic, well-drained soils. Although the importance of oxygen limitations on OM preservation is well recognized in marine and lacustrine sediments, the cumulative impact of such anaerobic microsites on OM mineralization rates and ultimately C storage in upland soils remains largely ignored by soil carbon models. Probably the single most important reason for this lack of recognition is the absence of a practical, low cost method to parameterize the abundance of anaerobic microsites in soil. Here we hypothesized a) that metabolic heterogeneity in soil would be reflected in small-scale variations of soil redox potentials and that b) such heterogeneity should be directly linked to parameters describing soil structure. To test our assumptions, we characterized the spatial variability of redox potentials by deploying sets of platinum redox probes within standardized soil volumes both in the laboratory and in the field. Soil structure was parameterized with the help of X-ray computed tomography. Metabolic heterogeneity within a soil horizon is minimized when the system is either completely saturated or completely dry. High amplitudes of heterogeneity were observed when the system was in transition between those states. Soil structure mainly determines rates of change and the absolute magnitude of heterogeneity. We posit that inexpensive redox electrodes constitute a practical way of characterizing the metabolic heterogeneity of a soil horizon.

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See more from this Division: ASA Section: Climatology & Modeling
See more from this Session: Biophysical Measurements and Sensors: II

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