Thursday, November 8, 2007 - 10:15 AM
341-7

Three Dimensional Distribution of Mm Scale Porosity in Soils Under Elevated CO2 and Temperature Conditions.

Hyen Chung Chun1, Daniel Gimenez1, Lewis Ziska2, Kate George3, and Richard Heck4. (1) Environmental Sciences, Rutgers, The state university of New jersey, 14 College Farm Road, new brunswick, NJ 08901, (2) USDA-ARS, 10300 Baltimore Avenue, Bldg 001, Room 323, BARC-WEST, Beltsville, MD 20705, (3) Crop Systems and Global Change Laboratory, USDA-ARS, 10300 Baltimore Avenue, Beltsville, MD 20705, (4) Land Resource Science, University of Guelph, Guelph, ON N1G 2W1, Canada

Modern human activities have increased concentration of atmospheric CO2 and temperature.  These increases will affect ecological systems at a global scale.  Plant productivity, root biomass, biodiversity in soils, and microorganisms has all shown to respond to high levels of CO2 and greater temperatures. Soil pore structure plays an important role in ecological systems because it conditions the environment of roots and microorganisms. Changes in aggregate size distribution exposed to higher levels of carbon dioxide have been documented, but there is no direct measurement of pore structure under those conditions. The objective of this study was to characterize spatial distribution of porosity at the mm-scale from 3D images of soil sampled from sites located along a natural gradient of CO2 and temperature.  Three sites from urban (P1), suburban (P2), and rural (P3) areas in Maryland were excavated and filled with the same soil in 2002.  In 2006, three undisturbed samples (5.5cm in diameter and 12cm in height) per site were taken and scanned with a computer tomographer at a resolution of 30 microns.  Images were binarized using Image J.  Image sizes ranged from 150 to 2,400 million voxels.  Images were divided in cubes containing 17 cubic voxels (P1) and 32 cubic voxels for (P2 and P3).  Theses cube sizes were selected as characteristic volume based on an entropy analyses.  Microporosity distributions from 3D soil images showed differences in pore structures under elevated CO2 and temperature.  In addition, spatial variability analysis provided information of micropores and macropores structures.

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