PARENT SESSION
Contributed Oral Session 39: Physiology: Respiration, Sap Flow, and Growth
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal
The contribution of a belowground inorganic carbon source to plant NPP: fixation of soil DIC by Pinus taeda seedlings.
Ford, Chelcy*,1, 2, Wurzburger, Nina1, Hendrick, Ronald1, Teskey, Robert1, 1 University of Georgia, Athens, GA2 USDA FS Coweeta Hydrologic Lab, Otto, NC
ABSTRACT- The contribution of belowground external inorganic carbon to plant net primary productivity (NPP) has been estimated to range between 0 and 5%. The potential contribution could be greater under scenarios of increased NH4+ assimilation (and associated amino acid biosynthesis), as anaplerotic reactions are needed to replenish TCA cycle carbon intermediates. We quantified the contribution of soil dissolved inorganic carbon (DIC) to total plant NPP and root system NPP under high and low NH4+ availability for Pinus taeda seedlings using 13C-labeled DIC. We hypothesized that 1) the contribution of soil DIC to total plant and root system NPP would be greater under NH4+ fertilization compared to without, and that 2) soil DIC would be relatively more important to root system NPP compared to whole-plant NPP. Seedlings exposed to labeled soil DIC were significantly more enriched than control seedlings (non-labeled soil DIC), -4.05 vs. -30.71 per mil, respectively. The distribution of carbon from soil DIC fixation differed between NH4+ treatments and tissue types. On average, 55% of soil DIC that was detected in the seedling ended up in the aboveground tissues. Of what remained belowground, significantly more carbon ended up in mycorrhizal roots and significantly less carbon ended up in woody roots of seedlings with NH4+ additions compared to those without. Greater carbon enrichment of mycorrhizal roots suggests NH4+ assimilation created a greater demand for anaplerotic reactions and soil DIC supplemented these reactions. Supplying plants with more NH4+ did not significantly increase the contribution of soil DIC to total plant or to root system NPP; however, plants receiving NH4+ fixed a greater percentage of available DIC in transpired water than plants without NH4+ additions. On a whole-plant basis, the contribution of soil DIC to total plant NPP ranged 0.16-0.92%; whereas soil DIC contributed a larger percentage to root system NPP, ranging 0.29-1.60%.
Key words: stable isotope, CO2