The fate of xylem-transported CO2 in plants

Author

Samantha S. Stutz, University of New MexicoFollow
David T. Hanson, University of New Mexico - Main CampusFollow

Publication Date

Summer 7-28-2018

Abstract

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

Language

English

Keywords

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

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

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

Recommended Citation

Stutz, Samantha S. and David T. Hanson. "The fate of xylem-transported CO2 in plants." (2018). https://digitalrepository.unm.edu/biol_etds/275