Physical Geog: A trip to Hortus Botanicus, Amsterdam

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]