[permaculture] C4 carbon fixation - Wikipedia, the free encyclopedia

Lawrence London lfljvenaura at gmail.com
Wed Mar 18 01:12:07 EDT 2015


>From a Reddit thread:
"In looking into Xeriscaping, I discovered -C4 Carbon Fixation- a plant
biochemical pathway evolution that greatly enhances the plant's efficiency
of water usage. Time to compile a list of C4 plants, to help California
from the so-called Megadrought.
(en.wikipedia.org <http://www.reddit.com/domain/en.wikipedia.org/>)"

" making an organism use water more effectively would expand its habitat
and lead to unintended side effects, so its good to weigh all the

   - Plant Types: II. C4 Plants, Examples, and C4 Families
   - http://www.cropsreview.com/c4-plants.html
   - Green Roof Plants - C4 Plant List
   - What are different types of CAM and C4 plants?
   - https://answers.yahoo.com/question/index?qid=20101107180714AAuMOWd
   - C 4 plants in the deserts of China: occurrence of C 4 photosynthesis
   and its morphological functional types

C4 carbon fixation
>From Wikipedia, the free encyclopedia

*C4 carbon fixation* is one of three biochemical mechanisms, along with C3
<https://en.wikipedia.org/wiki/C3_carbon_fixation> and CAM photosynthesis
<https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism>, used in carbon
fixation <https://en.wikipedia.org/wiki/Carbon_fixation>. It is named for
the 4-carbon molecule present in the first product of carbon fixation in
the small subset of plants known as C4 plants, in contrast to the 3-carbon
molecule products in C3 plants.
C4 fixation is an elaboration of the more common C3 carbon fixation and is
believed to have evolved more recently. C4 and CAM overcome the tendency of
the enzyme RuBisCO <https://en.wikipedia.org/wiki/RuBisCO> to wastefully
fix oxygen rather than carbon dioxide in what is called photorespiration
<https://en.wikipedia.org/wiki/Photorespiration>. This is achieved by using
a more efficient enzyme to fix CO2 in mesophyll cells
<https://en.wikipedia.org/wiki/Mesophyll_cell> and shuttling this fixed
carbon via malate <https://en.wikipedia.org/wiki/Malate> or aspartate
<https://en.wikipedia.org/wiki/Aspartate> to bundle-sheath
<https://en.wikipedia.org/wiki/Bundle-sheath> cells. In these bundle-sheath
cells, RuBisCO is isolated from atmospheric oxygen and saturated with the CO
2 released by decarboxylation
<https://en.wikipedia.org/wiki/Decarboxylation> of the malate or
oxaloacetate. These additional steps, however, require more energy in the
form of ATP <https://en.wikipedia.org/wiki/Adenosine_triphosphate>. Because
of this extra energy requirement, C4 plants are able to more efficiently
fix carbon in only certain conditions, with the more common C3 pathway
being more efficient in other conditions.

Plants that use C4 carbon fixation

About 7,600 plant species use C4 carbon fixation, which represents about 3%
of all terrestrial species of plants. All these 7,600 species are
angiosperms <https://en.wikipedia.org/wiki/Angiosperm>. C4 carbon fixation
is less common in dicots <https://en.wikipedia.org/wiki/Dicot> than in
monocots <https://en.wikipedia.org/wiki/Monocot>, with only 4.5% of dicots
using the C4 pathway, compared to 40% of monocots. Despite this, only three
families <https://en.wikipedia.org/wiki/Family_%28biology%29> of monocots
utilise C4 carbon fixation compared to 15 dicot families. Of the monocot
clades containing C4 plants, the grass (Poaceae
<https://en.wikipedia.org/wiki/Poaceae>) species use the C4 photosynthetic
pathway most. Forty-six percent of grasses are C4 and together account for
61% of C4 species. These include the food crops maize
<https://en.wikipedia.org/wiki/Zea_mays>, sugar cane
<https://en.wikipedia.org/wiki/Sugar_cane>, millet
<https://en.wikipedia.org/wiki/Millet>, and sorghum
[17] <https://en.wikipedia.org/wiki/C4_carbon_fixation#cite_note-17> Of the
dicot clades containing C4 species, the order
<https://en.wikipedia.org/wiki/Order_%28biology%29> Caryophyllales
<https://en.wikipedia.org/wiki/Caryophyllales> contains the most species.
Of the families in the Caryophyllales, the Chenopodiaceae
<https://en.wikipedia.org/wiki/Chenopodiaceae> use C4 carbon fixation the
most, with 550 out of 1,400 species using it. About 250 of the 1000 species
of the related Amaranthaceae <https://en.wikipedia.org/wiki/Amaranthaceae>
also use C4.[10]

Members of the sedge family Cyperaceae
<https://en.wikipedia.org/wiki/Cyperaceae>, and numerous families of
Eudicots <https://en.wikipedia.org/wiki/Eudicot>, including the daisies
Asteraceae <https://en.wikipedia.org/wiki/Asteraceae>, cabbages Brassicaceae
<https://en.wikipedia.org/wiki/Brassicaceae>, and spurges Euphorbiaceae
<https://en.wikipedia.org/wiki/Euphorbiaceae> also use C4.
Converting C3 plants to C4

Given the advantages of C4, a group of scientists from institutions around
the world are working on the C4 Rice Project
to turn rice <https://en.wikipedia.org/wiki/Rice>, a C3 plant, into a C4
plant. As rice is the world's most important human food—it is the staple
food for more than half the planet—having rice that is more efficient at
converting sunlight into grain could have significant global benefits
towards improving food security
<https://en.wikipedia.org/wiki/Food_security>. The team claim C4 rice could
produce up to 50% more grain—and be able to do it with less water and

The researchers have already identified genes needed for C4 photosynthesis
in rice and are now looking towards developing a prototype C4 rice plant.
In 2012, the Government of the United Kingdom
<https://en.wikipedia.org/wiki/Government_of_the_United_Kingdom> along with
the Bill & Melinda Gates Foundation
<https://en.wikipedia.org/wiki/Bill_%26_Melinda_Gates_Foundation> provided
$14 million over 3 years towards the C4 Rice Project at the International
Rice Research Institute

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