In his article 'Running down to Rio' (2 May), Jeremy Leggett rightly focuses on the major climatic effects anticipated from an increasing atmospheric content of CO2. Another serious consequence is a declining protein content of leaves, fruits and seeds.
This will come about because the extra CO2 available to the leaves will go into sugars and their polysaccharide derivatives rather than into amino acids, the building blocks of polypeptides or proteins.
There is clear evidence of this effect on leaf nitrogen content. The leaves of most plants (C3 types) growing under higher CO2 regimes will be less nutritious for leaf-eating insects, or domestic animals like cattle. A lower leaf nitrogen content also means that less serine and glutamine can be transported to the seeds. This will lower the ceiling for protein content for important food sources such as the legumes and wheat.
David Murray University of Sydney, Australia
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