Biology ETDs

Publication Date

Summer 7-28-2018


The concentration of carbon dioxide in tree stems can be ~30-750 times higher than current atmospheric [CO2]. Dissolved inorganic carbon enters the xylem from root and stem respiration and travels with water through the plant. However, the fate of much of this xylem-transported CO2 is unknown. In these studies I examined the fate of xylem-transported CO2 traveling through the petiole and leaf. This was accomplished by placing cut leaves from a woody and herbaceous C3 species, and a Kranz-type C4 species, in a solution of dissolved NaH13CO3 at concentrations similar to those measured in nature. This allowed me to track the efflux of 13CO2 using tunable diode laser absorption spectroscopy and compare this with 12CO2 fluxes derived from plant metabolism.

The objective of the first study was to measure the efflux of xylem-transported CO2 out of the woody species Populus deltoides and the herbaceous C3 species Brassica napus in the dark by testing the relationship among the concertation of bicarbonate in the xylem, the rate of transpiration, and the rate of gross CO2 efflux. I found when the concentration of CO2 in the xylem is high and when the rate of transpiration is also high, the magnitude of 13CO2 efflux can approach half of the rate of respiration in the dark.

The second study extends measurements of the fate of xylem-transported CO2 into lighted conditions where photosynthesis is active. I measured 12CO2 and 13CO2 fluxes across light- and CO2-response curves with the objectives of: 1) determining how much and under what conditions xylem-transported CO2 exited cut leaves in the light, and 2) determining how much xylem-transported CO2 was used for photosynthesis and when the overall contribution to photosynthesis was most important. I found that in the light the contribution of xylem-transported CO2 is most important when intercellular [CO2] is low which occurs under high irradiance and low [CO2].

The last study focused on the efflux and use of xylem-transported CO2 in the Kranz-type C4 species, Amaranthus hypochondriacus. Species with Kranz anatomy have highly active photosynthetic cells surrounding the vascular bundle, which is where xylem-transported CO2 would first interact with photosynthetic cells. The objectives of this study were to determine: 1) the rate and total efflux of xylem-transported CO2 exiting a cut leaf of the Kranz-type C4 species, A. hypochondriacus, in the dark and 2) the rate and contribution of xylem-transported CO2 to total assimilation in the light for A. hypochondriacus. Rates of dark efflux of xylem-transported CO2 out of A. hypochondriacus leaves were lower in the dark compared to rates observed in B. napus across the same rates of transpiration and bicarbonate concentrations. In the light a higher portion of xylem-transported CO2 was used for photosynthesis in A. hypochondriacus compared to B. napus suggesting that Kranz anatomy influences how C4 plants use xylem-transported CO2 for photosynthesis.

Project Sponsors

UNM Biology Department




Ameranthus hypochondriacus, Brassica napus, stem [CO2], Populus deltoides, tunable diode laser absorbance spectroscopy, xylem-transported CO2

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Degree Name


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Department Name

UNM Biology Department

First Committee Member (Chair)

David T. Hanson

Second Committee Member

Nathan McDowell

Third Committee Member

Robert Teskey

Fourth Committee Member

Kathy Steppe