HR: 0830h
AN: B31C-0301    [PDF]
TI: Rhizosphere C flux from tree roots to soil: spatial and temporal differences between sugar maple and yellow birch saplings
AU: * Phillips, R P
EM: rpp6@cornell.edu
AF: Cornell University, Fernow Hall, Ithaca, NY 14853
AU: Fahey, T J
EM: tjf5@cornell.edu
AF: Cornell University, Fernow Hall, Ithaca, NY 14853
AB: Rhizosphere carbon flux (RCF) has rarely been measured for intact root-soil systems. We measured RCF for eight year-old saplings of sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) collected from Hubbard Brook Experimental Forest and transplanted into 35 cm diameter pots with native soil horizons intact. We hypothesized birch roots which support ectomycorrhizal fungi would release more C to the rhizosphere than sugar maple roots which support vesicular-arbuscular mycorrhizal fungi. Saplings (n=5) were pulse-labeled with $^{13}$CO$_{2}$ at ambient CO$_{2}$ concentrations for 4-6 hours, and the label was chased through rhizosphere and bulk soil pools in organic and mineral horizons for 7 days. We observed immediate appearance of the label in rhizosphere soil, and there was a striking difference in the temporal pattern of $^{13}$C concentration between species. In maple, peak concentration of the label appeared at day 1 and declined over time whereas in birch the label increased in concentration over the 7 day chase period. As a result, total RCF was 2-3 times greater from birch roots. We estimate at least 5% and 10% of NPP may be released from this flux pathway in sugar maple and yellow birch saplings respectively. These results suggest that rhizosphere C flux likely represents a substantial proportion of NPP in northern hardwood forests, and may be influenced by trees species and mycorrhizal association.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting