PARENT SESSION
Poster Session 32: Biogeochemistry
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Variation in root exudation rates across a CO2 gradient.

Waters, Matthew^*,1, Bernhardt, Emily², Wetzel, Robert¹, ¹ University of North Carolina at Chapel Hill, Chapel Hill, NC, USA² Duke University, Durham, NC, USA

ABSTRACT- The ability of forests to sequester additional carbon under rising atmospheric CO₂ depends in large part on their ability to access sufficient nutrients. One mechanism by which plants can increase their access to soil nutrients is through root exudation, which may stimulate rhizosphere nutrient cycling. We examined whether loblolly pine trees can alter their exudation rates in response to differences in atmospheric CO₂ concentrations. Loblolly pine seedlings were grown from seed in growth chambers in the Duke Phytotron. Plants were randomly assigned to one of four CO₂ treatments (200 ppm, 360 ppm, 560 ppm, and 720 ppm). After 100 days, seedlings were removed from sand, rinsed and transplanted into hydroponic root growth chambers. Solution was added to chambers using peristaltic pumps which periodically flushed each chamber with 10% Hoagland′s solution. Solution was collected from each chamber throughout a 24 hour incubation period, stored on ice and then filtered through 0.25m nylon filters immediately after the incubation. Subsamples of filtered solution were analyzed for TOC and low molecular weight organic acids using HPLC. The remaining solution was put through a C18 resin filter to trap larger molecular weight organic compounds. These resin disks were extracted in methanol, compounds were separated using thin layer chromatography, and dominant compounds were identified using GCMS. Early results show a significant effect of CO₂ on the total amount of carbon in solution, indicating that exudation rates are increased with higher CO₂.

Key words: exudates, CO₂, rhizosphere, carbon