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Summary Traditionally, leaves were thought to be supplied withCO2for photosynthesis by the atmosphere and respiration. Recent studies, however, have shown that the xylem also transports a significant amount of inorganic carbon into leaves through the bulk flow of water. However, little is known about the dynamics and proportion of xylem‐transportedCO2that is assimilated, vs simply lost to transpiration.Cut leaves ofPopulus deltoidesandBrassica napuswere placed in eitherKCl or one of three [NaH13CO3] solutions dissolved in water to simultaneously measure the assimilation and the efflux of xylem‐transportedCO2exiting the leaf across light andCO2response curves in real‐time using a tunable diode laser absorption spectroscope.The rates of assimilation and efflux of xylem‐transportedCO2increased with increasing xylem [13CO2*] and transpiration. Under saturating irradiance, rates of assimilation using xylem‐transportedCO2accounted forc.2.5% of the total assimilation in both species in the highest [13CO2*].The majority of xylem‐transportedCO2is assimilated, and efflux is small compared to respiration. Assimilation of xylem‐transportedCO2comprises a small portion of total photosynthesis, but may be more important whenCO2is limiting.
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What is the fate of xylem‐transported CO 2 in Kranz‐type C 4 plants?
Summary High concentrations of dissolved inorganic carbon in stems of herbaceous and woody C3plants exit leaves in the dark. In the light, C3species use a small portion of xylem‐transported CO2for leaf photosynthesis. However, it is not known if xylem‐transported CO2will exit leaves in the dark or be used for photosynthesis in the light in Kranz‐type C4plants.Cut leaves ofAmaranthus hypochondriacuswere placed in one of three solutions of [NaH13CO3] dissolved in KCl water to measure the efflux of xylem‐transported CO2exiting the leaf in the dark or rates of assimilation of xylem‐transported CO2* in the light, in real‐time, using a tunable diode laser absorption spectroscope.In the dark, the efflux of xylem‐transported CO2increased with increasing rates of transpiration and [13CO2*]; however, rates of13CeffluxinA. hypochondriacuswere lower compared to C3species. In the light,A. hypochondriacusfixed nearly 75% of the xylem‐transported CO2supplied to the leaf.Kranz anatomy and biochemistry likely influence the efflux of xylem‐transported CO2out of cut leaves ofA. hypochondriacusin the dark, as well as the use of xylem‐transported CO2* for photosynthesis in the light. Thus increasing the carbon use efficiency of Kranz‐type C4species over C3species.
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- Award ID(s):
- 1301346
- PAR ID:
- 10443346
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 223
- Issue:
- 3
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 1241-1252
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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