[Prev][Next][Index][Thread]
Re: C4 vs. C3 (a little botany)
In article <19940614122230.niemirab@safir.bpp.msu.edu> niemirab@student.msu.edu (Brendan A. Niemira) writes:
The significant fact about C4 plants is that they are designed to grow in some
pretty nasty climates. C4 metabolism, coupled with Crassulacean Acid Metabolism,
allows growth in deserts, on mountains, tundra, etc. The poor C3 plants must
necessarily capture and subsequently incorportate their CO2 while the sun
shines, so they open their pores to get the CO2 during the day; the heat and
wind dries them out and they die. Those clever C4 plants, however, open their
pores at NIGHT and capture the CO2 when the air is cooler, so they won't dry
...
Interesting fact:
The C4 plants are more effecient overall because at low CO2 concentrations,
(about 180-250 ppm, Earth's atmospheric CO2 conc. up until a few years ago)
the more expensive method is more cost-effective. However, growth chamber
studies have shown that at higher CO2 concentrations (about 380-400 ppm), the
more expensive method isn't needed, and the C3 plants are more efficient,
overall, and therefore more competitive. Current CO2 concentration is 375 ppm
and rising. Screw global warming, we're talking about ecological collapse
due to differential CO2 fixative capacity. Ooops.. should have posted to
sci.ecology.conspiracy
My understanding was that C4 mechanism became competitive because
geochemical processes have been depleting the atmospheric CO2 on
very long time scales. Go back O(10^7) years and CO2 concnetrations
were ideal for C3. In fact there was a series of articles recently
in Nature about future CO2 depletion due the erosion of the Himalayas
and the impending collapse of C3 plants and associated ecosystems.
For a while it was the frontrunner for "first natural process to
terminate life on Earth" - time scale was 1-2 \times 10^8 years
as I recall, much shorter than, for example, solar evolutionary
time scale.
* Steinn Sigurdsson Lick Observatory *
* steinly@lick.ucsc.edu "standard disclaimer" *
* I know people whose idea of fun *
* Is throwing stones in the river in the afternoon sun *
* Oh let me be as free as them *
* - BB 1986 *
References: