Photosynthetic pathway influences xylem structure and function in Flaveria (Asteraceae)
Ferit Kocacinar1, Athena D McKown, Tammy L Sage
1Faculty of Forestry, Kahramanmaras Sutcu Imam University, Merkez 46100 Kahramanmaras, Turkey.
Plant, Cell & Environment
|July 23, 2008
Summary
Higher water use efficiency (WUE) in C4 plants may improve xylem safety. This study found that increased WUE during C4 evolution correlated with decreased hydraulic conductivity, suggesting a trade-off.
Area of Science:
- Plant Physiology
- Evolutionary Biology
- Ecology
Background:
- C4 plants exhibit higher water use efficiency (WUE) than C3 plants, potentially due to reduced transpiration rates.
- This higher WUE might offer greater xylem safety by minimizing water loss.
- The genus Flaveria provides a model system to study the evolution of C4 photosynthesis and its associated traits.
Purpose of the Study:
- To investigate the relationship between water use efficiency (WUE) and xylem safety during the evolution of C4 photosynthesis.
- To compare stem hydraulics and anatomy across C3, C3-C4 intermediate, C4-like, and C4 species within the Flaveria genus.
- To determine if increased WUE in C4 evolution is linked to changes in hydraulic conductivity and xylem structure.
Main Methods:
- Comparative analysis of stem hydraulics (leaf-specific conductivity, K(L); xylem-specific conductivity, K(S)) and xylem anatomy (vessel length, width, and frequency).
- Measurement of water use efficiency (WUE) across 16 Flaveria species representing different photosynthetic types (C3, C3-C4, C4-like, C4).
- Phylogenetic analysis to assess independent evolution of C4-like photosynthesis and associated trait correlations.
Main Results:
- C3 species exhibited the highest leaf-specific conductivity (K(L)), while perennial C4 and C4-like species had the lowest.
- Xylem-specific conductivity (K(S)) was generally higher in C3 species compared to intermediate and C4 species.
- Water use efficiency (WUE) was approximately double in C4-like and C4 species relative to C3-C4 and C3 species.
- Xylem vessels were shorter, narrower, and more frequent in C3-C4, C4-like, and C4 species than in C3 species.
- Correlated changes indicated that increased WUE promoted a decline in K(L) during C4 evolution, with WUE's involvement occurring late in the evolutionary sequence.
- C3-C4 species showed reduced K(L) but minimal WUE change, suggesting hydraulic efficiency reduction preceded WUE increases.
Conclusions:
- The evolution of C4 photosynthesis in Flaveria involves a trade-off between water use efficiency (WUE) and hydraulic conductivity (K(L)).
- Increased WUE during C4 evolution is associated with a decline in hydraulic efficiency, likely due to anatomical changes in xylem structure.
- Reductions in hydraulic efficiency appear to precede significant increases in WUE during the early stages of C4 evolution.
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