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Expedition Six
Space Chronicles #16

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By: ISS Science Officer Don Pettit

Light and the Production of Food

Nature often gives us clues on how to do things if we are only willing to listen. After observing the jungles of South America and of Africa from orbit, one notices how dark the landscape appears. Jungles are about the darkest land features you can observe in full sunlight. They are so dark you need to open your camera lens a stop and a half to obtain an exposure that shows any detail. If there are thin clouds masking part of your view, you are fooled into thinking you are over the ocean. When you notice rivers with braided channels and meandering loops of chocolate brown, onlythen do you realize that it is jungle and not water.

The multi-layers of abundant jungle life seem to suck up every photon that falls into the area. This is exactly how things should be if you want to efficiently use light for photosynthesis. Any ray of light that escapes the jungles is lost energy for growth, hence, life. And we all know how hard life is in the jungle.

When you pass over farmland, rich with vibrant crops, you see something different. Farmland is bright, much brighter than the jungles. You need to close down your lens by perhaps two stops to obtain similar film densities. This is a factor of four. About four times more light leaves our farmlands than jungles. Nature is giving us a clue, by example, of what is possible for the efficiency of light capture. Imagine what we could do with our agriculture if we only captured light with the same efficiency as the jungles? Might there be some new way that yields similar use of photons? However, our agriculture efficiency is very high as it is and includes another important factor: time. Mature jungles take years to develop. We grow and harvest our crops all within a few months. The kinds of plants we raise for food crops require direct sunlight to do well. Delicate orchids grown in deep shade do not yield much food value.

It appears there is a trade-off between efficient use of light and the maximum production of plant-derived biomass for food. It does seem that our agriculture is well optimized for efficient production of food but perhaps there is some room for some improvement, if we are only willing to listen.