Taking a trip to Amsterdam
with friends who were visiting found me at the Hortus
Botanicus botanical gardens this past weekend. This somewhat vintage
feeling herbarium is home to thousands of plants, divided into exhibits focused
on species from different biomes all over the world. I found the gardens
fascinating, particularly since I just completed an ecohydrology module a
couple of weeks ago.
Out of the three climate
greenhouses, the desert zone was especially interesting for me having just
covered this climate region in class, learning was framed in such a way that
the photosynthetic pathways and water uptake methods were particularly
emphasized. The desert zone housed a myriad of cacti and succulents, but this
post will hone in one in particular, Cereus hildmannianus.
The common name for this species of cactus is ‘Queen of the night’ and is
usually found growing in South America – particularly in Paraguay, Brazil,
Argentina and Uruguay (Braun et al., 2013).
As with other plants
similar to Cereus hildmannianus, in
order to survive in the harsh environment of the desert, it has adapted ways
that aid with photosynthesis and water preservation. Cereus hildmannianus is a fleshy species with think cuticles to
reduce water loss. This species has adapted a Crassulacean acid metabolism
(CAM) pathway for photosynthesis, which allows for the conversion of light to
energy whilst conserving water. Through the deployment of this CAM pathway, the
stomata of Cereus hildmannianus open
when the external temperature is low and moisture levels are high – reducing
evapotranspiration. Carbon dioxide exchange takes place at night with this
species when there is no incoming solar radiation and water levels in the
atmosphere are high – the carbon dioxide enters the leaf cells where it is then
incorporated in an organic acid. During the day, when external temperatures are
high, the stomata remain closed, preserving moisture. The carbon stored from
the night is then used for photosynthesis and conversion into vital sugars for
survival (Oxfordreference.com.libproxy.ucl.ac.uk, 2017).
This method of photosynthesis is extremely water efficient, which is why
plants like Cereus hildmannianus are
most often found in the driest and hottest areas of the world. However, due to
the fact that the carbon storage and photosynthesis processes are separated by
time and take place either in the day or at night, this species and others alike
experience very slow growth. It almost appears to be the case that the species
is forfeiting speedy growth in lieu of survival in such a harsh environment.
References:
Braun, P., Larocca, J., Machado, M. & Taylor,
N.P. 2013. Cereus hildmannianus. The IUCN Red List of Threatened Species
2013: e.T152594A655087. http://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T152594A655087.en.
Downloaded on 07 February 2017.
Oxfordreference.com.libproxy.ucl.ac.uk. (2017). crassulacean acid
metabolism. [online] Available at: http://www.oxfordreference.com.libproxy.ucl.ac.uk/view/10.1093/acref/9780199641666.001.0001/acref-9780199641666-e-9303
[Accessed 7 Feb. 2017]
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