For too long, CAM [crassulacean acid metabolism, in which CO2 is fixed into an organic acid at night when stomata are open(!) in such plants and re-fixed via the Calvin–Benson–Bassham et al. Cycle – C3 photosynthesis during daylight, when stomata are shut(!!)…] has been on the plant physiological sidelines as a quirky bit of biochemistry at one end of the spectrum of photosynthetic variations-on-a-theme. But now it is poised to take centre stage as more water-efficient solutions for plant biology are sought as we enter a water-frugal age.
Famously, the water-use efficiency (WUE), which describes ‘a plant’s photosynthetic production rate relative to the rate at which it transpires water to the atmosphere’ (e.g. Lucas Cernusak et al.) of CAM plants is rather low, which is good. However, they do also tend to grow rather slowly – albeit in hotter climes than temperate ones – which is not so good if you are interested in high-yielding crops to feed a growing world population or generate lots of biomass in a hurry. But if you are concerned about the ability of today’s plants to cope with drier, warmer climates in future, CAM might have a lot to offer.
If a new transatlantic alliance has its way, CAM is set to invade the world of the C3 photosynthesisers with US$14.3 million of funding from the USA’s Department of Energy. The dosh will be dished out amongst the Universities of Nevada and Tennessee (in the USA), Liverpool and Newcastle (in the UK), and the USA’s Oak Ridge National Laboratory.
Although crops may benefit from this research in the longer term, a more immediate shorter-term goal is to engineer CAM into the fast-growing biomass energy tree poplar so it can cope better with anticipated future growing conditions. CAM, coupled with a genetically engineered semi-dwarf stature in poplar (Ani Elias et al.), may be a ‘negative double-whammy’ that can deliver tree phenotypes that are not only more water-use-efficient, but advantageous for short-rotation forestry and biomass energy purposes.
So no longer will CAM be the exclusive preserve of such exotics as pineapples, epiphytic orchids and Crassula species, and the notion of poplar as a ‘facultative CAM plant’ – a sort of Mesembryanthemum crystallinum of the temperate forest – might just be science fiction turned into science fact. However, if Ming Yuan et al.’s work on Camellia – ‘tree-like shrubs’ – is widely applicable, then CAM can be induced in C3 species (such as, say – and chosen entirely at random you understand – poplar) by the much cheaper option of fungus infection. Hmmm, who’ll be the first to tell the UK–USA team/DoE that..?