Tuesday, November 14, 2006 - 2:30 PM

New Approaches for Capturing Soluble Root Exudates: Effects of Elevated CO2, N and Mycorrhizal Species on Rates and Composition.

Richard Phillips, Duke Univ, Box 91000 B227 LSRC, Dept of Biology, Durham, NC 27705-4005

Soluble root exudates are notoriously difficult to collect in non-hydroponic systems because they are released in a narrow zone around roots and are rapidly assimilated by rhizosphere microbes.  This has substantially limited our understanding of their rates of release and chemical composition in situ, and by extension, their ecological significance.  We designed a novel experimental system for collecting root exudates from loblolly pine (Pinus taeda) seedlings and field-grown trees using cuvettes filled with sterile glass beads (200 - 800 micron diameter).  Glass beads were selected as the rooting medium after experimental tests revealed that the beads - unlike sand - were not a sink for carbon-based compounds.  In the seedling experiment, pine roots were inoculated with one of four ectomycorrhizal species in peat-vermiculite, transferred to bead-filled cuvettes, and placed in growth chambers for eight weeks.  Seedlings were exposed to one of two levels of atmospheric CO2 (380 and 580 ppm) and N (0.5 and 1.0 mM nutrient solution).  In the field, roots from 20 year-old pine trees were trained to grow into a soil-sand basin for eight weeks and then transferred to bead filled cuvettes.  The trees were exposed to two levels of atmospheric CO2 (380 and 580 ppm) and two levels of N availability at the Duke Forest FACE site.  Although neither method directly measures root exudation in native soil, both provide a close approximation of the soil environment, and allow for the collection and chemical characterization of exudates in response to global change factors.