‘Night-time’ photosynthesis helps plants survive

15 July 2004

Plants growing in the tops of forest canopies are able to survive thanks to a special type of ‘night-time’ photosynthesis, according to the latest research by Oxford plant scientists, recently published in Proceedings of the National Academy of Sciences USA (PNAS).

These plants, called epiphytes, have a relatively stressful existence, even in tropical rain forests, as they can be exposed to the severe drying effects of full sunlight, high temperatures and continual air movement.

Researchers at Oxford’s Department of Plant Sciences and the Smithsonian Tropical Research Institute have now found that many of them possess a special type of photosynthesis known as crassulacean acid metabolism (CAM). This enables plants to conduct most of their gas exchange with the atmosphere at night, when the air is relatively cool and humid, rather than during the day as in most plants.

By studying a large family of plants called bromeliads – which includes terrestrial species like pineapple as well as epiphytic species such as Spanish moss – the researchers have found that CAM photosynthesis is surprisingly widespread in this group. Having sampled approximately two-thirds of the 3000 species in this family, the researchers estimate that nearly half of all bromeliads possess CAM photosynthesis. Further, by conducting an analysis of evolutionary relationships amongst the bromeliads, the researchers infer that CAM photosynthesis has arisen multiple times within this family, most likely in response to geological and climatic changes in the late Tertiary.

Professor Andrew Smith, senior author of the paper, said: ‘Traditionally we’ve tended to think of typical CAM plants as succulent species like cacti, agaves and euphorbias, which inhabit semi-desert regions with seasonal rainfall. Our work on bromeliads shows that CAM photosynthesis has evolved many times in very different groups of plants, and that it’s surprisingly common amongst tropical epiphytes. This study emphasizes the tremendous diversity of life-forms in the canopy of tropical forests.’

The researchers hope this work will lead to a better understanding of the exact relationship between past climate and the evolutionary origins of CAM photosynthesis. This, in turn, could be useful in predicting the consequences of future climate change, both for natural ecosystems and for the agronomic performance of crop plants. ‘When we consider the potential impact of global warming and progressive desertification’, said Professor Smith, ‘there is going to be an urgent need to develop more stress-tolerant varieties of crop plants for cultivation in the world’s marginal lands.’