Stomatal valves on the leaves of vascular plants not only prevent desiccation but also dynamically regulate water loss to maintain efficient daytime water use. This latter process involves sophisticated active control of stomatal aperture that may be absent from early-branching plant clades. To test this hypothesis, we compare the stomatal response to light intensity in 13 species of ferns and lycophytes with a diverse sample of seed plants to determine whether the capacity to optimise water use is an ancestral or derived feature of stomatal physiology. We found that in seed plants, the ratio of photosynthesis to water use remained high and constant at different light intensities, but fern and lycophyte stomata were incapable of sustaining homeostatic water use efficiency. We conclude that efficient water use in early seed plants provided them with a competitive advantage that contributed to the decline of fern and lycophyte dominated-ecosystems in the late Paleozoic.

Item Type:	Refereed Article
Keywords:	stomata evolution
Research Division:	Biological Sciences
Research Group:	Plant biology
Research Field:	Plant physiology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the environmental sciences
UTAS Author:	McAdam, SAM (Dr Scott McAdam)
UTAS Author:	Brodribb, TJ (Professor Tim Brodribb)
ID Code:	82459
Year Published:	2012
Funding Support:	Australian Research Council (FT100100237)
Web of Science® Times Cited:	101
Deposited By:	Plant Science
Deposited On:	2013-02-04
Last Modified:	2013-05-15
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