Altering Photosynthesis to Increase Crop Yield: A Double-Edged Sword for Food Security?

7 December 2016 Mervyn Piesse, Research Manager, Global Food and Water Crises Research Programme

Background

Food production will need to increase to ensure there is enough food to meet demand from a larger global population. As there is limited unutilised arable land available, improving the efficiency and yield of crops will be a key part of increasing food production. A recent paper, published in the journal Science, suggests that crop productivity gains could be made by altering how plants react to changes in the intensity of sunlight. Other studies, however, suggest that increased yields can lead to lower nutritional content in crops, dampening the food security gains made by increased plant productivity.

Comment

Photosynthesis (the process plants use to convert sunlight into energy for growth) depends on the right amount of sunlight, too little and the plant does not develop fully, while too much causes it to expel some of the energy from sunlight as heat. Once the light levels have declined, however, it can take hours for plants to return to optimal rates of photosynthesis.

By using genetic engineering techniques, a University of Illinois research team claims to have been able to increase the biomass of tobacco plants, chosen for their ease of manipulation, by up to 20 per cent. Agricultural scientists believe the technique could be used in the production of other crops, possibly increasing productivity by up to 50 per cent. As increased photosynthetic efficiency also has the potential to reduce the amount of water lost by plants there could also be water saving benefits.

Plants have been genetically manipulated in the past. During the Green Revolution, the selective breeding of crops increased yields considerably. Norman Borlaug, an American agronomist who led initiatives that increased global food production, bred a variety of wheat with short, sturdy stems that could hold a greater amount of grain. These varieties were grown in Mexico, India and Pakistan and greatly improved the food security of these countries. The careful breeding of plants over millennia has enabled them to produce more food to feed a hungry world.

Selective breeding, however, has failed to improve the nutritional quality of food. Over the last 70 years, the nutritional value of food has declined by 40 per cent. If photosynthetic engineering is to play a role in the Second Green Revolution, and help ensure global food security, it will need to ensure that crops retain, or increase, their nutritional content.

While soil depletion is the main cause of less nutritious crops, the selective breeding of plants for higher yield has also played a part. Breeding crops to achieve higher yields appears to have inadvertently led to reduced nutrient concentrations. A paper, published by a team of American scientists in 2004, found that declining nutritional content in food was partly caused by a focus on improving the size, growth rate and pest resistance of crops without an accompanying focus on improving the nutritional quality. Advances in plant biology have enabled plants to grow bigger and more rapidly, but they have not improved the ability of plants to manufacture or absorb nutrients.

While increasing crop yields will increase the quantity of food it may not necessarily improve food quality. If global food security is to be better guaranteed in the future, a holistic approach that takes the yield and nutritional content of food crops into account will be necessary.

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