For the first time, plant scientists at the University of Oxford have computationally analysed the energy cost associated with Crassulacean Acid Metabolism (CAM) photosynthesis.
The study, published today in Nature Plants, found that CAM photosynthesis is three fold more energetically costly than conventional (C3) photosynthesis that occurs in the majority of plants including major crops such as rice and wheat.
CAM plants often occur in marginal environments and generally grow slowly. However, CAM plants used as crops can be highly productive under favourable growing conditions. Agave tequilana (yes, grown for tequila production) has a record yield of over 40 tonnes per hectare. How can these crops, with a huge additional energy cost, match the productivity of C3 crops?
Professor Lee Sweetlove and team attempted to tackle this question by quantitatively comparing the energy-use and efficiency of the metabolic networks of CAM and C3 leaves in relation to their overall energy budget.
The team computed quantitative estimates of the fluxes of the hundreds of different energy-consuming and producing reactions in the leaf metabolic network through computational modelling of CAM and C3 leaf metabolism.
"What we found was that another feature of CAM – the suppression of metabolic process known as photorespiration - saved energy, and this energy saving was sufficient to exactly offset the cost of the CAM cycle", said Professor Sweetlove.
One of the greatest threats to the future productivity of our agricultural systems is increasing global aridity. Already, 40% of the world's land is arid to the extent that it is not possible to grow current staple crops without supplementary irrigation.
"CAM plants require 80% less water than C3 plants. Our work shows that if CAM were to be engineered into C3 crops they would benefit from this massive water saving without suffering a penalty in terms of yield", said Professor Sweetlove.
The study also showed which of the different types of CAM would be most productive and which C3 crops would perform best with CAM – crops whose leaves store starch such as potato and soybean would do slightly better than those that store sugars such as wheat.