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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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This content will become publicly available on May 1, 2026
C4 photosynthesis, trait spectra, and the fast‐efficient phenotype
Summary It has been 60 years since the discovery of C4photosynthesis, an event that rewrote our understanding of plant adaptation, ecosystem responses to global change, and global food security. Despite six decades of research, one aspect of C4photosynthesis that remains poorly understood is how the pathway fits into the broader context of adaptive trait spectra, which form our modern view of functional trait ecology. The C4CO2‐concentrating mechanism supports a general C4plant phenotype capable of fast growth and high resource‐use efficiencies. The fast‐efficient C4phenotype has the potential to operate at high productivity rates, while allowing for less biomass allocation to root production and nutrient acquisition, thereby providing opportunities for the evolution of novel trait covariances and the exploitation of new ecological niches. We propose the placement of the C4fast‐efficient phenotype near the acquisitive pole of the world‐wide leaf economic spectrum, but with a pathway‐specific span of trait space, wherein selection shapes both acquisitive and conservative adaptive strategies. A trait‐based perspective of C4photosynthesis will open new paths to crop improvement, global biogeochemical modeling, the management of invasive species, and the restoration of disturbed ecosystems, particularly in grasslands.
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- PAR ID:
- 10614019
- Publisher / Repository:
- John Wiley and Sons
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 246
- Issue:
- 3
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- 879 to 893
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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