Tuesday, December 10, 2013

Survey of cool and warm season grasses

Most prairie and savanna restorationists are aware that there are two classes of grasses, distinguished by a fundamental property of photosynthesis (abbreviated C3 and C4). Many prairie grasses have the C4 pathway, and because of this are able to proliferate in warmer parts of the summer when other plants are suffering from moisture stress. For the most part, prairie grasses are warm season grasses, and savanna grasses are cool season grasses. The C3/C4 differentiation is a good example of evolution in action, and botanists have been able to explain at a fairly fundamental level how these two kinds of grasses differ.

I recently spent some time putting together a table that sorts out these two kinds of grasses, based on an extensive review that was published by S.S. Waller and J.K. Lewis in the Journal of Range Management (1979; vol. 32, pp. 12-28). Note that my table is just a subset of that of Waller and Lewis since they have a lot of grasses that we are not familiar with here in the Midwest.

As I indicated, the C3/C4 phenomenon is an interesting evolutionary development that relates to the ability of plants to tolerate drought. The explanation is fairly sophisticated, but the Wikipedia pages on this are very good. See this link. (What would be do without Wikipedia?)

Essentially, the C4 pathway permits plants to carry out photosynthesis during warm (or hot) summer conditions, making them able to outcompete C3 plants.

Note that in our temperate climate, the only C4 plants are grasses, but in the tropics many broadleaf plants have the C4 pathway.

It is interesting that although C4 plants represent only 5% of the Earth's plant biomass, and only 1% of the known plant species, they account for about 30% of terrestrial carbon fixation.


C3 and C4 grasses: abbreviated from Waller and Lewis

Genus
Common name
C3
C4
Agropyron
Wheat grass (not agricultural wheat, which is Triticum)
*

Agrostis
Bent grass
*

Andropogon
Big bluestem

*
Avena
Agricultural Oats
*

Bouteloua
Side oats

*
Bromus
Brome
*

Calamagrostis
Blue-joint
*

Dactylis
Orchard grass
*

Deschampsia
Hair grass
*

Dichanthelium (formerly Panicum)
latifolium; leibergii; oligosanthes; praecocius
Panic grass
*

Digitaria
Crab grass

*
Echinochloa
Barnyard grass

*
Elymus
Wild rye
*

Eragrostis
Love grass

*
Festuca
Fescue
*

Glyceria
Manna grass
*

Hordeum
Barley
*

Koeleria
June grass
*

Leersia
Rice cut grass
*

Lolium
Perennial rye grass
*

Muhlenbergia
Muhly grass

*
Oryza
Rice
*

Panicum virgatum
Panicum capillare
Some other species of Panicum are C3 grasses
Switch grass
Witch grass

*
Paspalum
Paspalum grass

*
Phalaris
Reed canary grass
*

Phleum
Timothy
*

Poa
Blue grass
*

Pragmites
Common reed grass
*

Schizachyrium
Little bluestem

*
Secale
Cereal rye
*

Setaria
Foxtail

*
Sorghastrum
Indian grass

*
Sorghum
Broom-corn

*
Spartina
Cord grass

*
Sphenopholis
Wedge grass
*

Sporobolus
Dropseed

*
Stipa
Needle grass
*

Triticum
Wheat
*

Zea
Corn

*


According to the Wikipedia article: "C4 carbon fixation has evolved on up to 40 independent occasions in different families of plants, making it a prime example of convergent evolution. C4 plants arose 25-32 million years ago (Oligocene)... and did not become ecologically significant until around 6-7 million years ago (Miocene). C4 metabolism originated when grasses migrated from the shady forest undercanopy to more open environments, where the high sunlight gave it an advantage over the C3 pathway."

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