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Crop Growth Response to Elevated CO2 in a Closed Ecological System
Dempster, W.F., Nelson, M., Silverstone, S. and Allen, J.P. 2009. Carbon dioxide dynamics of combined crops of wheat, cowpea, pinto beans in the Laboratory Biosphere closed ecological system. Advances in Space Research 43: 1229-1235.

The authors write that the Laboratory Biosphere (LB) is a closed ecological system of some 40 m3 with two soil planting beds (each 2.68 m2 by 30 cm deep) that is fitted with 12,000 watts of high pressure sodium lights that provide artificial illumination for plant growth on a 13-hour light/11-hour dark cycle.

What was done
Dempster et al. grew cowpeas on one of the LB's planting beds (2.68 m2), while the other bed was used to grow pinto beans (1.6 m2) and wheat (0.8 m2). This was done for a period of three months, while they measured the net fixation rate of carbon by the entire three-crop system during the greater portion of this "growing season."

What was learned
The four researchers present data indicating that relative to net photosynthesis at a CO2 concentration of 385 ppm, rates measured at 1000 ppm, 2000 ppm and 2800 ppm were 150%, 275% and 355% greater, respectively.

What it means
Dempster et al. conclude that the "high productivity from these crops and the increase of fixation rates with elevated CO2 concentration supports the concept that enhanced CO2 can be a useful strategy for remote life support systems," presumably on long manned space flights or on outposts on other planets or moons. We additionally note that these and many similar results further suggest the "useful strategy" of allowing the CO2 content of our own atmosphere to continue to rise, so that the not-so-remote life support system of the earth may continue to meet the food needs of the growing number of people living here.

Reviewed 16 September 2009