HR: 1340h
AN: B13B-1186    [Abstracts]
TI: Simultaneous Measurements of Leaf and Soil Carbon Dioxide Flux Using a Tunable Diode Laser
AU: * Hunt, J E
EM: HuntJ@LandcareResearch.co.nz
AF: Landcare Research, PO Box 40, Lincoln, 7640, New Zealand
AU: Barbour, M M
EM: BarbourM@LandcareResearch.co.nz
AF: Landcare Research, PO Box 40, Lincoln, 7640, New Zealand
AB: A portable photosynthesis system (Li-6400, Li-Cor, NE) and a through-flow soil chamber were used to continuously measure the gas exchange of leaf and below ground components in pots containing corn, Triticale and a non-planted control. Temperature was kept constant through-out the experiment, and measurements were made at 4 min intervals over a full diurnal light cycle. A tunable diode laser (TGA100A, Campbell Scientific, UT) was used to measure the concentration and stable isotopic composition (δ¹³C and δ¹⁸O) of the air entering and exiting both chambers. End-member isotope values were determined by short-term incubation of component parts in Tedlar bags, and the evolved gas was measured with the laser. These data were used to determine the isotopic signature of CO₂ derived from root respiration, microbial respiration of plant derived exudates and soil organic matter (SOM) to allow the partitioning of the total flux into component parts. The δ¹³C of SOM respiration was identical when measured with the soil chamber on the control pots and when using incubated samples from the same pots. However, incubation of the potting mix in the other treatments was more enriched (corn) and more depleted (Triticale) than the control, indicating that end-member determination of the original SOM was confounded by exudates from the plants. Using a mixing model to partition the soil respiration, and the δ¹³C of SOM from the control pots, corn roots contributed 25% and Triticale 72% of the below-ground respiration. Incubation of soil with the roots removed allowed non-root respiration to be partitioned into contributions from pre-existing SOM and more recent plant derived exudates for corn (23% recent carbon) and Triticale (36% recent carbon).
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting