Monday, February 28, 2011

Adaptation and Green Roof Plants

We've talked numerous times about the different types of photosynthesis in green roof plants and why understanding those processes are important.  To summarize yet again, CAM plants' stomata usually open only at night to preserve water; C4 plants have multiple and different cells, some deeply embedded within the leaf to fight desiccation; and C3 plants conduct photosynthesis across the leaf surface - rapidly producing carbohydrates but loosing much more water than C4 and CAM plants.

But what is really interesting is looking at collateral issues associated with photosynthesis processes.

Scientists tell us that the majority of C4 plants are typical of prairies or wide open grasslands and these plants developed during periods of earth's history where there were relatively low amounts of CO2.   C4 plants are highly efficient at taking what CO2 and N is available and utilizing both quite efficiently, keeping waste to a minimum.

C4 plant Echinacea purpurea, Asteraceae

C4 plant Echinacea purpurea, Asteraceae

C4 plants interestingly, according to Wikipedia and sources:

represent about 5% of Earth's plant biomass and 1% of its known plant species.[11] Despite this scarcity, they account for about 30% of terrestrial carbon fixation.[8] Increasing the proportion of C4 plants on earth could assist biosequestration of CO2 and represent an important climate change avoidance strategy. Present-day C4 plants are concentrated in the tropics (below latitudes of 45°) where the high air temperature contributes to higher possible levels of oxygenase activity by RuBisCO, which increases rates of photorespiration in C3plants.

Wikipedia goes on to state:

C4 carbon fixation has evolved on up to 40 independent occasions in different families of plants, making it a prime example of convergent evolution.[8] C4 plants arose around 25 to 32 million years ago[8] during the Oligocene (precisely when is difficult to determine) and did not become ecologically significant until around 6 to 7 million years ago, in the Miocene Period.[8] C4 metabolism originated when grasses migrated from the shady forest undercanopy to more open environments,[9] where the high sunlight gave it an advantage over the C3pathway.[10] Drought was not necessary for its innovation; rather, the increased resistance to water stress was a by-product of the pathway and allowed C4 plants to more readily colonise arid environments.[10]

Additionally, Mycorrhizal fungi associations with C4 plants may help the C4 species adapt to higher CO2 concentrations in the atmosphere.

Nature is blurring the lines between C3, C4 and CAM plants to produce species suited for evolving climates.

Finally, man too is working with genetic engineering and bioengineering to produce those robo-plants we discussed in previous blog posts.

Green roof botany is an evolving science.  Staying abreast of trends, research and discoveries is interesting and can certainly help the green roof designer in developing a successful plant schedule for the green roof project.

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