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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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Carbon isotope trends across a century of herbarium specimens suggest CO 2 fertilization of C 4 grasses
Summary Increasing atmospheric CO2is changing the dynamics of tropical savanna vegetation. C3trees and grasses are known to experience CO2fertilization, whereas responses to CO2by C4grasses are more ambiguous.Here, we sample stable carbon isotope trends in herbarium collections of South African C4and C3grasses to reconstruct13C discrimination.We found that C3grasses showed no trends in13C discrimination over the past century but that C4grasses increased their13C discrimination through time, especially since 1950. These changes were most strongly linked to changes in atmospheric CO2rather than to trends in rainfall climatology or temperature.Combined with previously published evidence that grass biomass has increased in C4‐dominated savannas, these trends suggest that increasing water‐use efficiency due to CO2fertilization may be changing C4plant–water relations. CO2fertilization of C4grasses may thus be a neglected pathway for anthropogenic global change in tropical savanna ecosystems.
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- Award ID(s):
- 2224317
- PAR ID:
- 10510773
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 243
- Issue:
- 2
- ISSN:
- 0028-646X
- Format(s):
- Medium: X Size: p. 560-566
- Size(s):
- p. 560-566
- Sponsoring Org:
- National Science Foundation
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