Sunday, 6 December 2009

Plumbing key to flowering plants’ evolutionary success

The evolution of an efficient water transport system may be how flowering plants came to dominate terrestrial plant life 60-70 million years ago.

According to Tim Brodribb at the University of Tasmania, efficient water-conducting vessels allowed flowering plants, called angiosperms, to double their photosynthetic rate, providing them with more carbon for growth and reproduction.

With their increased productivity, angiosperms overtook the then-dominant gymnosperms to represent more than 96 percent of vascular plant species today.

Plant plumbing


With Taylor Field at the University of Tennessee, Brodribb studied 504 living angiosperm species, as well as 89 living and 166 extinct non-angiosperm species.

The data set was analysed against fossil data to infer the evolution of angiosperms through time.

Early angiosperms were found to have relatively few water-conducting veins in their leaves. However, by the Late Cretaceous about 95 million years ago, angiosperms’ leaf vein density had increased by more than 150 percent, to become three times that of gymnosperms.

“Our study showed that very significant changes in the leaves of angiosperms occurred early in their evolution that changed them from being essentially just a flowering gymnosperm to being the powerhouses of modern biology,” Brodribb explains.

“Something happened late in the Cretaceous that enabled angiosperms to rapidly evolve leaves with very dense venation forming very highly efficient irrigation network which pushed photosynthetic performance far above their competitors.”

Darwin’s abominable mystery


In a letter to his friend Joseph Hooker in July 1879, Charles Darwin famously referred to the seemingly abrupt origin and rapid diversification of angiosperms as an ‘abominable mystery’.

There currently are no fossils or living ancestors that allow researchers to link angiosperms with their very different gymnosperm ancestors.

Meanwhile, the evolution of angiosperms has shaped climates and terrestrial biology, and is crucial to modern human civilisation because of our reliance on highly productive fruit, root and grain crops for food.

“All ecosystems were changed, pollinators evolved, the face of the planet was drastically modified indeed,” says Vincent Savolainen at the Imperial College London and Royal Botanic Gardens Kew.

“He [Darwin] was surprised that it was so sudden, angiosperms seemed to appear and hyper-diversify simultaneously.”

Brodribb hypothesises that declining humidity and carbon dioxide concentration during the Cretaceous may have caused angiosperms to increase leaf vein density in order to meet their transpirational requirements.

Moving forward, Brodribb and Field plan to study how leaves coordinate their photosynthetic performance with the development of plumbing.

1 comment:

Charles Weber said...

I suspect that you will find interesting a proposal that angiosperm plants evolved on the Ontong-Java Plateau before the Cretaceous in http://charles_w.tripod.com/ontong.html and below; You may see its publication in http://gsjournal.net/Science-Journals/Research%20Papers-Paleontology/Download/4719 . Also you may see an explanation for the boundaries of the temperate deciduous forest as a function of glaze ice storms in http://charles_w.tripod.com/glaze.html .
Sincerely, Charles Weber

PERMIAN MONSOON EVOLUTION OF ANGIOSPERMS to FURNISH DECIDUOUS GLAZE ICE TREES
by Charles Weber
Angiosperms had to have existed before the early Cretaceous when they appeared fully formed. I suspect they evolved since the Carboniferous on an island mini continent Angiosperm (also called magnoliophyta) deciduous dicotyledon trees have had much more success in surviving in glaze ice areas than other types of trees because of less branch breakage in winter time. They started to become established in North American subarctic regions in the Paleocene and were fully established before the Eocene closed. They probably descended largely from subtropical trees. I suspect that they may have evolved the precursor genes on a now submerged South Western Pacific mini continent, the Ontong Java Plateau, probably as early as the Permian, as a monsoon area adaptation. Their seeds were probably carried to the mainland on the feet of water birds and in the crops of seed eating birds.
18, 405.