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Plants are famous for their ability to photosynthesize. They produce sugars that are essential for life, using CO2 coupled with light energy from the sun. We know that photosynthesis occurs during daylight but what if we told you that in some plants, part of this process takes place in the dark of night? This unique process is known as Crassulacean Acid Metabolism or CAM photosynthesis and is a remarkable adaptation of some plants to hot and dry environments.   

As part of his thesis project, Hugh McGrath, a final year student at Trinity College Dublin set out to explore whether or not Cycadales, exhibit CAM photosynthesis, using an array of species available at Trinity College Botanic Garden.  

But why Cycads? Cycads peaked in diversity about 145 million years ago, during the Jurassic-Cretaceous period which is often termed ‘the age of cycads’. The Earth’s climate was hotter back then, with CO2 being as much as 4 times higher.  

Cycad diversity has dwindled since their Jurassic reign. Today, 300 species exist, limited to pockets of suitable tropical and sub-tropical climate, many threatened with extinction. But could it be that CAM photosynthesis aided the success of this ancient group of plants during ‘the age of cycads’?  

CAM plants have adapted to close their stomata during daylight. Stomata are tiny pores on plant leaves through which atmospheric CO2 enters the leaves and water is released, a process known as transpiration. Closing these pores during the day enables plants growing in areas of water scarcity to conserve this precious resource 

However, CO2 still remains essential for photosynthesis. CAM plants uniquely assimilate CO2 by opening their stomata at night. 

Hugh investigated the possible occurrence of CAM photosynthesis in the Cycads growing at TCBG. Overall, it was observed that 4 cycad species are potential exhibitors of CAM photosynthesis, supporting the case for further exploration of CAM in this ancient group of plants.